U.S. patent application number 11/030837 was filed with the patent office on 2005-06-23 for determination of wheel sensor position using radio frequency detectors in an automotive remote tire monitor system.
This patent application is currently assigned to Schrader Bridgeport International, Inc.. Invention is credited to Boudaoud, Idir, Stephen McClelland, Thomas David, Stewart, William David.
Application Number | 20050134446 11/030837 |
Document ID | / |
Family ID | 21803345 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050134446 |
Kind Code |
A1 |
Stewart, William David ; et
al. |
June 23, 2005 |
Determination of wheel sensor position using radio frequency
detectors in an automotive remote tire monitor system
Abstract
A tire monitor system and method rely on only two RF detector
mounted on the vehicle, one in close proximity to one of the front
wheels and the other in close proximity to one of the rear wheels.
An RF detector can distinguish between its local transmitter and
the other transmitter on the same axle by the amount of signal
received. Every time the controller decodes transmitted RF data,
the controller looks to see if and which RF detector has detected
the transmission. The controller can then determine over a short
period of time which sensor identifier belongs to which corner of
the vehicle.
Inventors: |
Stewart, William David;
(Antrim, IE) ; Boudaoud, Idir; (Creteil, FR)
; Stephen McClelland, Thomas David; (Craigavon,
IE) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Schrader Bridgeport International,
Inc.
|
Family ID: |
21803345 |
Appl. No.: |
11/030837 |
Filed: |
January 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11030837 |
Jan 7, 2005 |
|
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10021284 |
Oct 29, 2001 |
|
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6882270 |
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Current U.S.
Class: |
340/447 ;
340/686.1 |
Current CPC
Class: |
B60C 23/0437 20130101;
B60C 23/0444 20130101; B60C 23/0416 20130101 |
Class at
Publication: |
340/447 ;
340/686.1 |
International
Class: |
B60C 023/00 |
Claims
1. A tire monitor method comprising: at two or more detectors,
detecting envelopes of respective radio transmissions from two or
more tire monitors; and based on the detected envelopes of the
respective radio transmissions, identifying a source tire monitor
position.
2. The tire monitor method of claim 1 further comprising: based on
the detected envelopes, modulating a wireline signal; and
identifying the source tire monitor position based on the modulated
signal.
3. The tire monitor method of claim 1 further comprising: based on
the detected envelopes, determining a number of received
transmissions from each of the two or more tire monitors; and
identifying the source tire monitor position based on the number of
received transmissions.
4. The tire monitor method of claim 1 further comprising: based on
the detected envelopes, determining a rate of received
transmissions from each of the two or more tire monitors; and
identifying the source tire monitor position based on the rate of
received transmissions.
5. The tire monitor method of claim 1 further comprising: detecting
a signal envelope for the transmissions from a first tire monitor;
detecting a signal envelope for the transmissions from a second
tire monitor; and comparing the detected signal envelopes to
determine the source tire monitor position.
6. The tire monitor method of claim 5 further comprising: based on
the detected envelopes, counting received transmissions from the
first tire monitor; based on the detected envelopes, counting
received transmissions from the second tire monitor; and comparing
the transmission counts to determine source tire monitor
position.
7. The tire monitor method of claim 1 wherein detecting envelopes
comprises: modulating a wireline signal to indicate detection of
the envelopes of the respective radio transmissions.
8. The tire monitor method of claim 1 wherein detecting envelopes
comprises: in response to the respective radio transmissions,
controlling actuation of a circuit element conducting a current
which is detected to identify a position of a tire monitor
transmitting the respective radio transmissions.
9. A remote tire monitor system comprising: a first plurality of
tire monitors associated with wheels of a vehicle and configured
for transmission of radio signals conveying information; a second
plurality of detectors, each detector associated with a pair of
tire monitors to detect presence of radio signals from the pair of
tire monitors and to produce a detected transmission indication in
response to the detection of the presence of the radio signals; and
a control unit electrically coupled by conductors with the
plurality of detectors to receive detected transmission
indications, the control unit configured to receive tire monitor
transmissions and associate transmitting tire monitors with
positions on the vehicle based on the received detected
transmission indications.
10. The remote tire monitor system of claim 9 wherein each detector
of the second plurality of detectors comprises an envelope detector
responsive to the presence of the radio signals to produce a
wireline signal corresponding to an envelope of the radio
signals.
11. The remote tire monitor system of claim 10 wherein the envelope
detector modulates a current in a conductor electrically coupled
with the control unit in response to the presence of the radio
signals.
12. A remote tire monitor system comprising: tire monitors
mountable on wheels of a vehicle and configured for radio
transmissions of tire data; radio detectors, each radio detector
being configured to detect radio transmissions from tire monitors
according to proximity to the tire monitors and produce an
indication of a detected transmission, a first radio detector being
positioned near one of a first pair of tire monitors and a second
radio detector being positioned near a second pair of tire monitors
on the vehicle, each radio detector being positioned proximate one
tire monitor of its respective pair of tire monitors and positioned
distal the other tire monitor of its respective pair of tire
monitors; and a control unit which receives the radio transmissions
and which is coupled with the radio detectors to count the
indications produced by respective tire monitors, the control unit
determining respective positions of the tire monitors on the
vehicle based on counts of the indications.
Description
PRIORITY CLAIM
[0001] This application is a continuation of application Ser. No.
10/021,284 filed Oct. 29, 2001, which is hereby incorporated by
reference.
CROSS REFERENCE TO RELATED PATENT
[0002] This application is related to U.S. Pat. No. 6,518,876,
filed Apr. 25, 2000 and patented Feb. 11, 2003, in the names of
Emmanuel Marguet and William David Stewart and commonly assigned to
the owner of the present application. The U.S. Pat. No. 6,518,876
is incorporated herein in its entirety by this reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to a remote tire
monitoring system. More particularly, the present invention relates
to a method and apparatus for automatically updating position
information for tire monitors in such a system.
[0004] Systems have been developed to monitor a characteristic such
as tire pressure of a vehicle and to report the characteristic to a
receiver at a central monitoring station using radio transmissions.
A monitor is located at each tire and periodically takes a
measurement of the tire characteristic. The monitor then transmits
the results of the measurement in a radio frequency transmission to
the central monitoring station which produces an alarm or a display
in response to the measurement.
[0005] One problem with such systems has been the need to program
the location of the transmitters at the central station. To be
fully useful, the tire characteristic data is preferably associated
with the tire which originated the measurement when presenting a
display or alarm. Each monitor includes identification information
which can be transmitted with the measurement. The tire monitor is
preferably activated to produce this information and the
information is then conveyed to the central station and associated
with the position of the tire.
[0006] In the technique of U.S. Pat. No. 5,600,301, the tire
monitors each include a reed switch or other magnetic device. A
magnet is passed near the reed switch, causing the monitor to
transmit a radio frequency transmission that includes
identification data. A service technician repeats this process at
each wheel and then loads the identification and position
information into the central monitoring station. Another method
provides a printed bar code on each tire monitor which contains the
identification information and which may be read with a suitable
bar code reader.
[0007] In U.S. Pat. No. 5,880,363, an activation signal is provided
from the central controller to a low frequency transmitter at each
wheel well. The transmitter generates a low frequency signal to
activate the tire monitor. The tire pressure monitor responds by
generating a long wave identification signal and transmitting that
signal with tire pressure and identification data directly to the
control unit. The long wave identification signal is used to
identify the position of the tire by distinguishing this
transmission from other transmissions received by the
controller.
[0008] U.S. Pat. No. 5,883,305 discloses two-way communication of
data by radio signals. A tire pressure monitor is activated by a
radio frequency signal transmitted by an antenna in the wheel well
adjacent the tire. The tire pressure monitor transmits a second
radio frequency signal which is detected by the wheel well antenna.
The second signal is demodulated to detect that tire pressure
data.
[0009] These previous techniques have been limited in
effectiveness. The magnetic programming technique may be subject to
interference and crosstalk, for example in a factory where many
such tire monitors are being assembled with tires and vehicles. The
bar code label system requires a label at each tire which can be
lost or become dirty or illegible. The apparatus for transmitting a
long wave activation signal and generating a long wave
identification signal therefrom is too expensive for some
applications. The two-way data communication techniques requires
demodulation of the received radio signals at the wheel well and
coaxial cabling back to the central controller, both of which add
to the cost of the system.
[0010] A further limitation of some of these prior techniques is
the manual operation requiring activation by a service technician.
A system is desired which automatically conveys wheel position data
to the receiver. Such a system would be particularly useful after
any change in tire position, such as tire rotation or replacement
of a tire.
[0011] U.S. patent application Ser. No. 09/557,682, commonly
assigned with the present application, discloses a system and
method in which tire monitors are located at each wheel of the
vehicle and periodically transmit tire data along with a tire
monitor identifier. Four small, inexpensive RF detectors are
located near each wheel. Each RF detector is connected to the
central control unit by a power line and a ground line. When a tire
monitor transmits data by emitting an RF transmission, the RF
detector that is closest to the transmitter will detect the burst
of RF energy. The RF detector responds to the RF energy by
modulating the power line to the control unit with the envelope of
the transmitted data. The control unit detects this modulation on
one of its power lines. Also, the RF receiver of the control unit
receives and demodulates the data transmitted by the tire monitor.
The control unit associates the received data with the position
indication provided by the modulation on the power line. When the
positions of the wheels on the vehicle are changed, the control
unit can determine the new position using the modulated power line
in association with the tire monitor identifier in the transmitted
data.
[0012] While this system has been very successful in application, a
system featuring reduced cost and weight is desired. The cables
that must be run from the control unit to all four RF detectors add
substantially to the cost and weight of an installation.
Accordingly, there is a need for a system and method which provide
the operational advantages of the earlier system in a system
offering reduced complexity, parts count, weight and cost.
SUMMARY
[0013] By way of introduction only, a remote tire monitor method
and apparatus provide a central control unit in the cockpit or
trunk of a vehicle. The control unit includes a radio frequency
(RF) receiver and a controller. Tire monitors are located at each
wheel of the vehicle and periodically transmit tire data along with
a tire monitor identifier. Two small radio frequency (RF) detectors
are positioned in proximity to two wheels on the vehicle. The RF
detectors give an indication of the location of a transmitting tire
monitor to the controller.
[0014] The present embodiments of a tire monitor system and method
rely on only two RF detectors mounted on the vehicle, one in close
proximity to one of the front wheels and the other in close
proximity to one of the rear wheels. An RF detector can distinguish
between its local transmitter and the other transmitter on the same
axle by the amount of signal received. For example, if an RF
detector is positioned in close proximity to the left rear wheel,
then it can ideally expect to receive 100 percent reception from
the transmitter on the left rear wheel and ideally around fifty
percent reception from the right rear wheel's transmitter. The
amount of false triggering from the front wheel transmitters is
substantially zero. Every time the controller decodes transmitted
RF data, the controller looks to see if and which RF detector has
detected the transmission. The controller can then determine over a
short period of time which sensor identifier belongs to which
corner of the vehicle.
[0015] A method in accordance with one embodiment provides for
detecting transmissions from two or more tire monitors at a
detector. Then, based on a signal parameter associated with the
transmission, the method provides for identifying a source tire
monitor position. In one embodiment, the method further includes
determining the amount of signal received from the two or more tire
monitors and determining the signal parameter based thereon. In one
example, a signal strength may be used as the signal parameter or
to determine the signal parameter. In another, the number of
transmissions received at a detector from two or more tire monitors
may be used as the signal parameter or to determine the signal
parameter. In another example, signal to noise ratio may be used as
the signal parameter or to determine the signal parameter. In still
another example, instead or in addition to the number of
transmissions received, the rate of transmission reception may be
used as the signal parameter or to determine the signal
parameter.
[0016] In other embodiments, the signal parameter may be determined
for a first tire monitor and for a second tire monitor. The
respective signal parameters may then be compared to determine the
source tire monitor position.
[0017] In another embodiment, transmissions are received at a
central control unit of the vehicle and at the same time are
detected either by a front RF detector positioned near one of the
front wheels or a rear RF detector positioned near one of the rear
wheels. The number of transmissions received from each tire monitor
are counted and counts are maintained. After receipt of a
sufficient number of transmissions, the counts are compared to
determine the position of each tire monitor in the system.
[0018] An RF detector will detect almost all the transmissions from
an adjacent tire monitor (e.g., in the same wheel well) and some of
the transmissions from a tire monitor at the same end (front or
rear) of the vehicle, and substantially none of the transmissions
from tire monitors at the other end of the car. Therefore, based on
the number of received transmissions after a time and using the
tire monitor identification embedded in the transmissions, the tire
monitor positions can be deduced from the counts of the received
transmissions.
[0019] The foregoing discussion of the preferred embodiments has
been provided only by way of introduction. Nothing in this section
should be taken as a limitation on the following claims, which
define the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWING
[0020] FIG. 1 is a block diagram of one embodiment of a remote tire
monitor system shown in conjunction with portions of a vehicle;
[0021] FIG. 2 is a flow diagram illustrating one embodiment of an
auto learn method for the remote tire monitor system of FIG. 1;
[0022] FIG. 3 is a flow diagram illustrating one embodiment of an
auto learn method for the remote tire monitor system of FIG. 1;
[0023] FIG. 4 is a block diagram of a vehicle with a remote tire
monitor system; and
[0024] FIGS. 5 and 6 and are a flow diagram illustrating one
embodiment of a remote tire monitor system.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0025] Referring now to the drawing, it is a block diagram of a
remote tire monitor system 100 shown in conjunction with portions
of a vehicle 102. The vehicle 102 includes in this example four
tires 104. Other numbers of tires may be included, such as a fifth
tire as a spare or additional tires if the vehicle is a truck,
trailer or other multi-wheeled vehicle.
[0026] Associated with each of the tires 104 is a transmitter or
tire monitor 106. Each of the tire monitors 106 includes a battery
powered, radio frequency (RF) transmitter. Any suitable tire
monitor may be used. U.S. patent application Ser. No. 09/245,938,
entitled "Method And Apparatus For A Remote Tire Pressure Monitor
System," filed Feb. 5, 1999 in the name of McClelland et al., and
commonly assigned with the present application is incorporated
herein by reference and illustrates one suitable tire monitor for
use in the remote tire pressure monitor system 100. Each tire
monitor 106 includes a sensor such as a pressure sensor for
measuring a tire characteristic. The tire monitor 106 converts the
measured tire characteristic to tire data. The tire data is encoded
for transmission from the tire monitor 106.
[0027] The tire monitor further includes a transmitter configured
to transmit RF signals including the tire data. In some
embodiments, the transmissions are encoded or randomized to
minimize clashes at a receiver. For example, U.S. patent
application Ser. No. 09/245,577, entitled "Method For Communicating
Data In A Remote Tire Pressure Monitoring System," filed Feb. 5,
1999 in the name of Bailie, et al., and commonly assigned with the
present application is incorporated herein by reference. This
application shows a technique in which data words are transmitted
separated by a time delay. The time delay for each respective data
word is defined according to a repeating pattern common to the
tires so that data words are transmitted during a plurality of
aperiodic time windows. Transmission parameters such as modulation
techniques, transmission frequency and transmission power are
chosen according to local regulations and to assure reliable
reception of the RF signals.
[0028] The tire monitor 106 includes a motion switch 139. The
motion switch 139 closes upon detection of movement of the vehicle
100. The motion switch 139 provides a signal to the processor 124
indicating closure of the switch 139 and motion of the vehicle. In
response to closure of the switch, the tire monitor system 100
begins operating, for example, by transmitting tire data. In the
illustrated embodiment, during normal operation, the tire monitor
106 transmits supervisory tire pressure information once every
minute. Any suitable motion switch may be used for the switch
139.
[0029] The remote tire monitor system 100 includes a control unit
110 and a plurality of radio frequency (RF) detectors 112. In
alternative embodiment, the remote tire monitor system 100
additionally includes a user display for providing user information
such as tire pressure information and low tire pressure alarms. In
the illustrated embodiment, each RF detector 112 is mounted on the
vehicle 102 proximate an associated tire monitor 106 to detect the
RF signals from the associated tire monitor 106 and produce a
transmission indication in response to detected RF signals. Each of
the RF detectors 112 is electrically coupled by a conductor 114 to
the control unit 110. Structure and operation of the RF detectors
112 will be described in greater detail below.
[0030] The control unit 110 includes an RF receiver 120, an RF
decoder 122, and a controller 124. The RF receiver 120 is
configured to receive RF signals conveying tire data from at least
one transmitting tire monitor 106 of the plurality of tire monitors
106 associated with the wheels or tires 104 of the vehicle 102. Any
suitable RF receiver circuit may be used. The design and
implementation of the RF receiver 120 will depend on the type of
modulation used for the RF signals, transmission frequency for the
RF signals, and physical limitations such as permitted size, weight
and power dissipation.
[0031] The RF decoder 122 is configured to receive a transmission
indication from at least one receiving RF detector 112 of a
plurality of RF detectors 112 associated with wheels or tires 104
of the vehicle 102. Thus, a tire monitor 106 will transmit RF
signals which are detected by the RF detector 112 associated with
the transmitting tire monitor 106. The receiving RF detector 112
signals its detection of the RF signals by providing the
transmission indication on its associated conductor 114.
[0032] The RF decoder 122 is further configured to identify a
position of a transmitting tire monitor on the vehicle in response
to the transmission indication received from an RF detector.
Accordingly, the RF decoder 122 includes a plurality of input
circuits 123 coupled to the conductors 114 which are in turn
coupled to the RF detectors 112. A transmission indication
impressed on a conductor 114 is detected by an associated input
circuit 123. In the illustrated embodiment, there is a one-to-one
relationship between input circuits 123 and RF detectors 112. In
this manner, the RF detector 112 which originated the transmission
indication may be identified by the RF decoder determining which
input circuit 123 detects the transmission indication. In
alternative embodiments, the RF decoder 122 may include fewer than
four input circuits 123 which are multiplexed in some manner among
the plurality of RF detectors 112. For example, a single input
circuit 123 may be time shared among the plurality of RF detectors
112 to reduce the cost and complexity of the RF decoder 122.
[0033] The RF decoder 122 is electrically coupled with the RF
circuit 120. Upon receipt of RF signals at the RF circuit 120, the
RF signals are demodulated to extract the tire data contained
within the RF signals. In some applications, additional data
decoding may be required after demodulation. The tire data in one
exemplary embodiment includes a tire monitor identifier, or unique
identification code which uniquely identifies the tire monitor 106
which transmitted the RF signals. In addition, in this exemplary
embodiment, the tire data also includes tire pressure data related
to a sensed tire pressure of the tire 104 at which the transmitting
tire monitor 106 is located. Alternative tire data may be included
or substituted for the tire pressure data, such as a number of tire
revolutions, tire temperature, and so forth.
[0034] After extracting the tire data from the RF signals, the tire
data is conveyed from the RF receiver 120 to the RF decoder 122.
The RF decoder 122 associates the tire data with a position of the
transmitting tire monitor 106 on the vehicle 102. Position
information is determined using the input circuit 123 and a
transmission indication received over a conductor 114 from RF
detector 112. The tire data and associated tire position are
conveyed from the RF decoder 122 to the controller 124.
[0035] The controller 124 controls the operation of the remote tire
monitor system 100. The controller 124 is preferably a
microcontroller including a processor 128 and a memory 126. The
processor 128 operates in response to data and instructions stored
in the memory 126 to control overall operation of the system
100.
[0036] In the illustrated embodiment, the processor 128 stores
position data for a plurality of tire monitors 106 of the remote
tire monitor system 100. The controller 124 is electrically coupled
to the RF decoder 122 to receive tire data and position data from
the RF decoder 122. In the illustrated embodiment, when tire data
and position data are received at the microcontroller 124, the
processor 128 retrieves stored position data from the memory 126.
In one embodiment, the position data are stored in association with
a position on the vehicle, such as left front, left rear, right
front or right rear. The received position data is compared with
the stored position data. If there is no change, the position data
is not updated and further processing may occur using the received
tire data. However, the processor 128 updates the position data for
the transmitting tire monitor 106 when the position of the
transmitting tire monitor 106 varies from the stored position data
for the transmitting tire monitor. Thus, the controller 124
includes a memory 126 and a processor configured to store in the
memory 126 position of the plurality of tire monitors 106 including
the position of the transmitting tire monitor which originated the
received position data.
[0037] In an alternative embodiment, the memory 126 is not used for
storage of position data. Rather, the received tire data is
associated by the control unit 110 with the position information
provided by the transmission indication from a RF detector 112. The
tire data and the position information from the input circuit 123
are used together to produce a display or alarm, if appropriate, by
the system 100. Additionally, in still another embodiment, the tire
data omits any identifying information for the transmitting tire
monitor 106 and again, the tire data and the position information
from the input circuit 123 are used together to produce the
appropriate display or alarm.
[0038] Completing the identification of the elements in FIG. 1, the
vehicle 102 further includes a CAN driver 130, a voltage regulator
132, power line noise suppressor 134, and a battery 136. The
battery 136 provides operating power for electrical systems of the
vehicle 102 including the remote tire monitor system 100. The
battery 136 is a portion of the electrical power system of the
vehicle, which typically also includes an alternator and other
components. Such electrical power systems for vehicles are well
known. The power line suppressor 134 reduces noise on the power
line from the battery 136. Noise may originate in other electrical
components of the vehicle 102, such as the ignition system. The
voltage regulator 132 receives the battery voltage or other
operating voltage from the power line suppressor 134 and produces a
well regulated voltage for components such as the control unit 110
and CAN driver 130. The CAN driver 130 provides electrical
interface with other elements of a Controlled Area Network.
Controlled Area Network or CAN is a serial communication protocol
for data commonly used in automotive and other applications. The
CAN bus 138 accessed by the CAN driver 130 is used to interconnect
a network of electronic nodes or modules. The CAN bus operates
according to an adopted standard. In conjunction with a remote tire
pressure monitor system 100, the CAN bus 138 may be used to convey
tire monitor data to other locations in the vehicle 102. For
example, an alarm or a display (not shown) may be controlled to
provide a visual or audible indication to an operator of the
vehicle 102 that the tire data indicates an out-of-range condition,
such as low tire pressure.
[0039] In FIG. 1, the RF decoder 122 and the controller 124 are
shown as separate elements of the control unit 110. In alternative
embodiments, they may be combined in a single processor or logic
block or circuit. Any other illustrated elements or additional
elements included to enhance the functionality of the system 100
may be integrated or combined with other components of the system
100.
[0040] Further, the system 100 should not be restricted to use in
conjunction with a CAN bus. In alternative embodiments, any other
communications medium may be employed for interconnecting the
system 100 with other elements of the vehicle 102. For example,
communication buses in accordance with the J-1850 or USB standards
may be substituted, or the control unit 110 may be directly hard
wired with other elements of the vehicle 102. Still further,
external communications may be omitted entirely so that the system
100 is completely self-contained.
[0041] FIG. 1 further shows a detailed view of one embodiment of an
RF detector 112 for use in the remote tire monitor system 100. The
RF detector 112 includes an antenna 140 to sense radio frequency
(RF) signals transmitted from the tire monitor 106, an amplifier
142, an envelope detector coupled to the antenna 140 through the
amplifier 142 and an output circuit 146 coupled to the envelope
detector 144. The envelope detector 144 includes a filter 149, a
diode 150, a capacitor 152 coupled to ground and an amplifier 154.
The RF detector 112 is powered from a power line 156 and a ground
line 158 provided on the conductor 114 which couples the RF
detector 112 to the input circuit 123 of the RF decoder 122. To
isolate the operational circuitry of the RF detector 112 from noise
on the power line 156, the RF detector 112 further includes a
resistor 160 and a capacitor 162 to ground.
[0042] The envelope detector 144 responds to the input signals
received at the antenna and amplified by the amplifier 142 to
produce at the output circuit 146 data corresponding to the
envelope of the RF signals transmitted by the tire monitors 106.
Thus, the filter 148, diode 150 and capacitor 152 together form a
circuit coupled with the antenna 140 to detect an envelope of
electrical signals produced by the antenna in response to the RF
signals. The envelope is itself an electrical signal which is
amplified in the amplifier 154. The output signal from the
amplifier 154 is applied to the base of a transistor 164. In
response to this signal at its base, the transistor 164 modulates a
wire line signal on the conductor 114 in response to the envelope
of the RF signals received at the RF detector 112. That is, the
signals applied at the base of the transistor 164 control turn-on
of the transistor 164, conducting current from its collector at the
power node of the conductor 114 to its emitter at the ground node
of the conductor 114. As a result, the current in the conductor 114
will be modulated in response to the RF signals received at the
antenna 140 of the RF detector 112.
[0043] In one embodiment, to detect the modulated current, the
input circuits 123 of the RF decoder in the illustrated embodiment
may include a current mirror which duplicates the current drawn
from the input stage of the input circuit 123, coupled to the
conductor 114. The output current from the current mirror in the
input circuit 123 is provided to a resistor which converts the
current signal into a voltage signal which can be read by the
microcontroller 124. Suitable current mirror circuits are within
the purview of those ordinarily skilled in the art of circuit
design.
[0044] In this manner, then, the signal provided on the conductor
114 forms a transmission indication indicating that the tire
monitor 106 associated with the RF detector 112 has transmitted an
RF signal which was detected by the RF detector 112. Producing the
transmission indication includes detecting the envelope of the RF
signals transmitted by the tire monitor 106 and producing a
wireline signal on the conductor 114 in response to the envelope of
the RF signals. In particular, in the illustrated embodiment, the
wireline signal is produced by modulating a current in a conductor
114 coupled with the control unit 110. The control unit 110 detects
the modulation of the current to locate the transmitting tire
monitor 106.
[0045] Significantly, the RF detector 112 does not demodulate the
data transmitted by the tire monitor 106. Only the RF circuit 120
of the control unit 110 demodulates the data to extract the
contents of the RF signal 106. The RF detector only senses the
presence of the transmitted RF signals. This reduces the cost of
the RF detectors 112 and the overall cost of the remote tire
monitor system 100.
[0046] Also, by modulating the current in the conductor 114, the RF
detector's sensitivity to noise is reduced. Noise will occur in the
form of voltage spikes or pulses on the conductor 114. However,
this noise will have little effect on the operation of the RF
detector 112 and will have little effect on the current levels in
the conductor. As a result, the conductor 114 can be, for example,
a twisted pair of wire or any other inexpensive two-wire cable.
Coaxial cable or other shielded cable is not necessary for
implementing the system 100 using RF detector 112.
[0047] In alternative embodiments, the RF circuit 120 may be
omitted. In such an embodiment, the RF detectors 112 are used to
detect the variations in the radio frequency signals and modulate a
wire line signal on the conductors 114. The RF decoder 122 in such
an embodiment is configured to demodulate the data in conjunction
with the microcontroller 124. Current pulses on the conductor 114
are detected by the RF decoder 122 and converted to voltage pulses.
The voltage pulses can be read by the microcontroller 124. In this
manner, microcontroller 124 obtains the data from the RF detectors
and the RF decoder, without use of an RF circuit 120. This has the
advantage of eliminating the relatively expensive RF circuit.
Further, this permits reduction in the transmit power used by the
tire monitors 106 to transmit the radio frequency signals conveying
the entire data. In some jurisdictions, substantially attenuated
transmit power is required for applications such as tire monitors.
These low transmit power requirements may be satisfied while still
providing reliable performance in the remote tire monitoring system
100 by use of the RF detectors 112.
[0048] In still other embodiments, the functionality described
herein may be implemented using a programmed computer or other
processor operating in response to data and instructions stored in
memory. The processor may operate in conjunction with some or all
of the hardware elements described in the embodiments shown
herein.
[0049] The disclosed tire monitor system may be used to provide an
improved auto learn or auto train method for automatically
identifying positions of a plurality of tire monitors on a vehicle.
As noted above, previously devices such as a transponder or
magnetic activation tools were used in the car plant to train the
control unit of the remote tire monitor system with identifiers for
the wheel sensors or tire monitors. With the vehicle located in a
training booth or activation area at the factory, the wheel sensors
were activated in sequence and the control unit, expecting
activated pressure transmissions in a certain order, learned the
identification and position on the vehicle of the wheel sensors. So
as to prevent cross talk from other training booths, each
activation area is required to be RF shielded. Another method of
training the receivers was to use bar code readers to scan the
identifiers of the wheel sensors and input this data into the
receiver. All of these methods required an additional operation
either manually or by automatic readers. These operations add cost
and potential for downtime.
[0050] In the illustrated embodiment of FIG. 1, no such tools are
required. In the car plant at the end of the production line, a
standard one to two minute dynamic test is used to test and
calibrate steering, brakes etc. of the vehicle. For the illustrated
embodiment, positions and identities of the four tire pressure
monitor wheel sensors are automatically learned during this dynamic
test.
[0051] This is achieved by placing the control unit or receiver in
a "learn state" at a dynamic test booth. The wheel sensors transmit
either once a minute as in the normal mode, or in a special initial
mode corresponding to a brand new, right out of the box state,
transmitting more often, for example every 30 seconds, or every 10
seconds.
[0052] For example, when the wheel sensors leave the manufacturer's
production line, they are placed in off mode. This mode means that
each wheel sensor is dormant until it is activated by the closing
of its motion switch. Closing the motion switch is only achievable
through centrifugal force caused by spinning the tire monitor on a
rotating wheel. During normal operation, the wheel sensor, while
driving, transmits tire information including supervisory tire
pressure once every minute. However, in the illustrated embodiment,
for the driving periods during the first 16 activations of the
motion switch, the wheel sensor will transmit the supervisory
pressure data once every 30 seconds (to conform to United States
regulatory requirements) or 10 seconds outside the United States.
Other time intervals may be used. After the initial 16
transmissions, or any other suitable number, the transmission
interval is changed to its normal mode value, such as one minute.
This initial mode is known as factory test mode.
[0053] At the time of the dynamic vehicle test, the vehicle is
accelerated, causing the wheel sensors to activate with the
rotation of the wheels and associated closure of their motion
switches. When the wheel sensors begin transmitting tire pressure,
say once every thirty seconds, each sensor's identifier is
transmitted by the sensor and is received up by the RF circuit of
the control unit. In this initial unlearned state, the receiver
loads the new identifier into memory, associating the transmission
with one of the four RF detectors. Only data received which also is
synchronized to activity on one of the RF detector conductors is
regarded as valid. Over the one to two minute duration of the
dynamic test, each wheel sensor will transmit numerous times and
the control unit can verify the tire information, such as each
wheel sensor identifier, and associated wheel position. The control
unit can then load this data into non-volatile memory for
subsequent normal use.
[0054] Key advantages of this auto-learn technique is the lack of
any additional labor or equipment at the vehicle assembly plant,
and the lack of a need for a transponder component or magnetic
switch in the wheel sensor. Also there is no possibility of
learning the wrong wheels, from other vehicles due to cross talk or
of getting the wrong position. Thus, cost is reduced, operation is
simplified and reliability is increased. Using the illustrated
embodiment of the tire monitor system, no additional activation or
learning tools are required to train the control unit with the
wheel sensors' position on the vehicle. The only device required to
train the control unit is the standard dynamic vehicle test at the
end of line test in the vehicle assembly plant. Because the
training procedure can be carried out in parallel with the steering
and braking tests on the rolling road, and because of the factory
test mode feature, no extra time or cost is required to `auto
learn` the tire monitor system.
[0055] The illustrated embodiment further provides for automatic
update of tire monitor position information in the control unit
upon replacement of one of the tire monitors of the system. This
would occur, for example, if one of the wheels or tires of the
vehicle is replaced. Due to the nature of the current embodiment,
where the RF detectors are continuously indicating the position of
the wheel sensors, a wheel sensor may be replaced and detected by
the control unit without the need for user intervention. In this
case, where a new wheel sensor is put on a wheel, the control unit
initially realizes it is receiving a wrong identifier for the tire
monitor, but still getting RF detector pulses from a particular
wheel position. In addition, the control unit detects that the
previously stored identifier for that position is no longer being
received. Over a period of time, say ten minutes driving, the
receiver verifies it has stopped receiving a stored identifier and
is now receiving a new ID for that position. After verification,
the new identifier is stored for that position and operation
continues as normal.
[0056] The big advantage of this is the lack of need for user
intervention and elimination of the need for a service tool at each
service location. Tire monitor position and identification is
updated automatically.
[0057] FIG. 2 is a flow diagram illustrating an auto learn method
for the remote tire monitor system of FIG. 1. The method begins at
block 200. At block 202, one or more tires with new tire monitors
are mounted on a vehicle which includes a remote tire monitor
system. In this embodiment, the tire monitors are in unused, out of
the box condition from the manufacturer. The installation of block
202 may occur as part of the final assembly of the vehicle at the
factory. Alternatively, the installation may occur when new tires
are installed on the vehicle or when a remote tire monitor system
is added to the vehicle.
[0058] At block 204, the dynamic vehicle test is initiated and, in
response, at block 206, the tire monitors begin transmitting radio
frequency (RF) signals. The dynamic vehicle test is a test to check
proper functionality of the systems of the vehicle, including drive
train and brakes. Alternatively, any activity which causes the tire
monitors to begin transmitting may be substituted at block 204 to
initiate transmission at block 206. For example, the process of
driving the vehicle from the end of the assembly line to a storage
area or a final checkout area in block 204 may be adequate to begin
transmission at block 206. It is contemplated that the tire
monitors each include a motion switch which activates the tire
monitor in response to motion of the tire monitor on the wheel of
the vehicle.
[0059] Further, at block 206, the tire monitor begins transmitting
at a test mode interval, such as once every 30 or 60 seconds. This
aspect may be omitted but adds convenience for initializing the
tire monitor system. After initialization, the interval may be
reduced to reduce power drain from the battery which powers the
tire monitor.
[0060] After transmission of the RF signals at block 206, the RF
signals are received by a receiver of the remote tire monitor
system at block 208. The RF signals are demodulated, decoded and
otherwise processed to extract the data conveyed on the RF signals.
For example, the tire monitor may modulate a carrier signal using
data corresponding to pressure of the tire or a tire monitor
identifier. The receiver of the remote tire monitor system
demodulates the received RF signals to receive the data. At block
212, the data including a tire monitor identifier, if any, is
provided to a control unit of the remote tire monitor system.
[0061] Meanwhile, the same RF signals received and demodulated at
blocks 208, 210 are detected at block 214. In the preferred
embodiment, the RF signals are received without demodulation, for
example, using a detector of the type illustrated above in
conjunction with FIG. 1. Other suitable RF detectors may be used.
At block 216, in response to the detected RF signals, a
transmission indication is provided to the control unit. The
transmission indication indicates to the control unit which RF
detector of the vehicle detected the RF signals transmitted by the
tire monitor and received by the receiver at block 208.
[0062] At block 218, identification information associated with the
tire monitor is stored. In one embodiment, the data forming the
identifier transmitted by the tire monitor and received by the
receiver of the remote tire monitor system is stored in memory.
Other types and formats of identification information may be
stored. For example, the control unit may store an RF detector
indicator which indicates which RF detector detected the received
RF signals.
[0063] In this manner, the described method provides automatic
learn capability in a remote tire monitor system. No manual
intervention is necessary for the control unit to identify and
store the identities and locations of individual tire monitors on
the vehicle. This reduces time and cost associated with initiating
operation of the remote tire monitor system.
[0064] FIG. 3 is a flow diagram illustrating an auto learn method
for the remote tire monitor system of FIG. 1. The method of FIG. 3
starts at block 300.
[0065] At block 302, RF signals transmitted by a tire monitor
associated with a wheel of a vehicle are received by a receiver of
the remote tire monitor system. At block 304, the RF signals are
demodulated, decoded and otherwise processed to extract the data
conveyed on the RF signals. For example, the tire monitor may
modulate a carrier signal using data corresponding to pressure of
the tire or a tire monitor identifier. The tire monitor identifier
may be a serial number or other unique or nearly-unique data
associated with the tire monitor. For example, the tire monitor
identifier may be multiple bit data stored in the tire monitor at
the time of manufacture of the tire monitor. The receiver of the
remote tire monitor system demodulates the received RF signals to
receive the data. At block 306, the data including a tire monitor
identifier, if any, is provided to a control unit of the remote
tire monitor system.
[0066] Meanwhile, the same RF signals received and demodulated at
blocks 302, 304 are detected at block 308. In the preferred
embodiment, the RF signals are received without demodulation, for
example, using a detector of the type illustrated above in
conjunction with FIG. 1. Other suitable RF detectors may be used.
At block 310, in response to the detected RF signals, a
transmission indication is provided to the control unit. The
transmission indication indicates to the control unit which RF
detector of the vehicle detected the RF signals transmitted by the
tire monitor and received by the receiver at block 302.
[0067] At block 312, stored identification information is retrieved
from memory at the control unit. In the illustrated embodiment, the
identification information is stored at a memory location
associated with the transmission indication or RF detector. Thus,
the control unit receives a wireline indication from a receiving RF
detector that a transmission has been received. Using the wireline
indication, the control unit selects the memory location from which
previous identification information is retrieved.
[0068] At block 314, the control unit determines if the identifier
received from the transmitting tire monitor matches the stored
identification information. In this application, a match may mean a
bit-by-bit match of received and stored data or some other level or
association between the received data and the stored data. If the
data match, at block 316, the tire information such as pressure
data are updated. For example, in one embodiment, tire pressure
data are stored along with the identification information for the
tire monitor. If the received tire pressure data varies by a
predetermined amount from the stored tire pressure data, the
received tire pressure data is stored and an alarm or other user
indication is generated.
[0069] At block 318, if there is no match between the received
identifier and the stored identification information, the method
waits for receipt of an additional transmission associated with
this RF detector. Preferably, the tire monitor transmits pressure
data and a tire monitor identifier periodically, such as once per
minute. Upon receipt of a subsequent transmission, at block 320,
the method attempts to verify the previously received tire monitor
identifier. This is done by comparing the newly received tire
monitor identifier and the previously received tire monitor
identifier to determine if there was an error in communication of
the previously received tire monitor identifier. In some
embodiments, multiple subsequent transmissions may be received for
comparison. If there is no verification, at block 322, the
mismatched transmission received at block 302 is discarded. This
condition indicates that the same tire monitor continues to
transmit, and the mismatched transmission was received with an
error.
[0070] If at block 320 the newly received data verify the
previously received data, the identification information stored for
this RF detector is updated with the tire monitor identifier from
the received transmission. This condition indicates that the tire
monitor has been changed and is communicating reliably. In this
manner, the illustrated system and method provide automatic update
capability after a tire monitor has been changed. This may occur if
the tires of the vehicle are rotated or if one or more tires is
replaced. There is thus no need to manually intervene for the
remote tire monitor system to update the identities and locations
of the tire monitors on the vehicle.
[0071] FIG. 4 is a block diagram of a vehicle 400 with a remote
tire monitor system 402. In the exemplary embodiment of FIG. 4, the
vehicle 402 includes wheels 404, 406, 408, 410. Each wheel includes
a tire mounted on a rim. In other embodiments, the vehicle 400 may
have other numbers of wheels. For example, in one particular
embodiment, a truck has 18 wheels.
[0072] The remote tire monitor system 402 includes a control unit
412, a front detector 414 and a rear detector 416. The front
detector 414 is electrically coupled to the control unit 412 by a
cable 418. Similarly, the rear detector 416 is electrically coupled
to the control unit 412 by a cable 420.
[0073] The remote tire monitor system 402 further includes a tire
monitor associated with each wheel of the vehicle 400. Thus, a tire
monitor 424 is associated with wheel 404; tire monitor 426 is
associated with wheel 406; tire monitor 428 is associated with
wheel 408; and tire monitor 430 is associated with wheel 410. The
tire monitors are generally of the type described herein and are
configured to detect a tire condition such as tire pressure and to
occasionally transmit a transmission including tire data, such as
tire pressure data and identification information uniquely
identifying the respective tire monitor.
[0074] In the illustrated embodiment, the front detector 414 is
positioned proximate the left front wheel 404. For example, the
front detector 414 may be mounted in the wheel well adjacent the
wheel 404. Similarly, the rear detector 416 is positioned near the
left rear wheel 408, such as in the wheel well adjacent the wheel
408. With this mounting configuration, the front detector 414 is
positioned to detect transmissions from the pair of tire monitors
424, 426 associated with the front wheels 404, 406. The front
detector 414 is proximate the left front tire monitor 424 and
distal the right front tire monitor 426. Similarly, the rear
detector 416 is positioned to detect transmissions from the left
rear tire monitor 428 and the right rear tire monitor 430. The rear
detector 416 is positioned proximate the left rear tire monitor 428
and distal the right rear tire monitor 430.
[0075] The illustrated embodiment is exemplary only. In FIG. 4, the
detectors 414, 416 are designated for detecting radio frequency
transmissions from the front wheels 404, 406 and the rear wheels
408, 410, respectively. In alternate embodiments, the RF detectors
414, 416 may be positioned to detect RF transmissions from the left
side wheels 404, 408 and the right side wheels 406, 410
respectively. Similarly, while in FIG. 4 the front detector 414 is
positioned in proximity to the left front wheel 404, away from the
right front wheel 406, this positioning may be reversed so that the
front detector 414 is positioned near the right front wheel 406,
such as in the left front wheel well. In the same way, the rear
detector 416, shown in FIG. 4 in proximity to the left rear wheel
408, may be positioned in proximity to the right rear wheel 410.
Actual positioning of the RF detectors 414, 416 is not important.
Rather, the relative signal strength or frequency of reception of
RF transmissions from tire monitors is what is measured by the
detectors 414, 416 in conjunction with the control unit 412. It is
important that each RF detector be positioned on one side or end of
the car, away from the centerline, so that the relative signal
strength or number of transmissions received by the RF detector
from each of its associated pair of tire monitors can be
determined.
[0076] The control unit 412 includes a receiver to receive radio
frequency transmissions from tire monitors of the tire monitor
system 402, a controller 432 and a memory device 434. The
controller 432 forms a processing means and may be any suitable
control device such as a microprocessor, microcontroller,
application specific integrated circuit (ASIC) or logic device
coupled together to perform the necessary functions described
herein.
[0077] The memory device 434 forms a memory means for storing data
and preferably is formed of semiconductor memory. In the
illustrated embodiment, the memory device of the control unit 412
includes persistent memory or nonvolatile memory such as an
E.sup.2PROM, and working memory such as random access memory (RAM).
For example, the persistent memory may be used to stored tire
identifiers and pressure data over extended periods of time, such
as when the vehicle 400 is parked. The RAM may be organized as an
array which stores counter values associated with tire monitor
identifiers and tire monitor positions, as will be described in
greater detail below.
[0078] FIG. 5 is a flow diagram illustrating operation of one
embodiment of a remote tire monitor system. The method illustrated
in FIG. 5 may be used in conjunction with a remote tire monitor
system of the type illustrated in FIG. 4. The method embodiment in
FIG. 5 allows a control unit of such a system to automatically
learn the positions of the tire monitors of the system on the
vehicle, referred to as a learn method or learn routine. This
determination is made after receiving several transmitted frames of
tire data from the respective tire monitors of the system. The
control unit establishes an array of data in working memory and
uses the data of the array to determine the position information
for each tire monitor in the system. An example array of data is
illustrated below.
1 FrontRFD Rear RFD TotalRF_FrameCounter id1 22 2 22 id2 12 4 23
id3 2 20 20 id4 1 10 20
[0079] In this example, rows of the array are defined by the
identification information for each tire monitor from which data
are received. In the example above, the identification information
is listed as "id1," "id2," etc. However, in a more typical example,
the identification information will be a numeric value forming a
unique identifier or identification code of a transmitting tire
monitor. The identification code is typically transmitted along
with the tire pressure or other tire data by the tire monitor in a
transmission frame. The exemplary array is shown with four rows,
one for each tire monitor of the vehicle in this example. The array
may also be formatted with additional rows to record data for
additional transmitting tire monitors whose transmissions are
received by the controller.
[0080] In the example array above, the columns of the array
correspond to frame counter values which count the number of frames
received at the respective RF detector of the system. Thus, in this
example, a frame labeled with tire monitor identifier id1 has been
received at the front RF detector 22 times. A frame with the same
identifier id1 has been received at the rear RF detector two times,
and so on. The count label TotalRF_FrameCounter is a count of the
total number of frames received by the receiver of the controller
from the identified tire monitor. The total frame counts recorded
in this column is always greater than or equal to an RFD frame
counter because the receiver has greater sensitivity than the RF
detectors and detects transmissions that are missed by the RF
detectors.
[0081] The method of FIG. 5 begins at block 500. The method of FIG.
5 shows the learn routine on the production line, when the tires of
the vehicle are first assembled with the tire monitors and added to
the remote tire monitor system. At block 502, it is determined if
tire identifiers are already stored in electrically erasable
(E.sup.2) memory. This memory is nonvolatile or persistent memory
which retains data stored therein even when power is removed from
the memory. In the illustrated system, after installation on a
vehicle, the persistent memory is empty. As soon as tire
identifiers are received and verified according to the procedure of
FIG. 5, the tire monitors are stored in the persistent memory.
Thus, block 502 determines if this is the first time the tire
monitor system has been operated after installation on a vehicle.
If so, no tire monitor identifiers will be stored in the persistent
memory and the "no" path will follow to block 504. If tire
identifiers are already stored in the persistent memory, the "yes"
path is followed to block 602.
[0082] At block 504, it is determined if a frame of data has been
received. If not, control remains in a loop including block 504
until a frame of data have been received. As indicated above, each
frame of data transmitted by a tire monitor typically includes data
corresponding to the tire identifier which uniquely identifies the
transmitting tire monitor and tire data, such as data corresponding
to the measured tire pressure of the tire. Other information, such
as a header or synchronization data may be transmitted as well.
[0083] Once a frame of data has been received at block 504, the
tire monitor identifier contained in the frame of data is extracted
and compared with other already-received identifiers stored in the
list in working memory. If the extracted tire identifier is not
present in the list, block 506, it is added to the list, block 508.
Control then proceeds to block 510, where the relevant wheel
position counters are incremented. As noted above, each identifier
has three associated counters. One counter each is associated with
each RF detector of the system and stores data corresponding to the
number of transmissions detected by that respective RF detector.
The third counter counts the total frames received from an
identified tire monitor, and is incremented after a frame is
received at the receiver of the controller. Thus, the relevant
wheel position counters that are incremented at block 510 include
the total RF frame counter and the frame counter corresponding to
the front RF detector or the rear RF detector.
[0084] At block 512, a test is performed to determine if the
specified criteria have been fulfilled. First, it is determined if
four tire identifiers in the list have Total RF Frame counter
values that are greater than a predetermined number, 20 in this
example. That is, before applying the pass criteria, at least four
tire identifier counters must have a value of 20 or greater. This
test is implemented to ensure that there is a strong signal from a
tire monitor and to eliminate any wrong or incorrect tire
identifiers being added to the system. If the received signal from
a tire monitor is weak, it will likely be received only a few
times, rather than 20 or more times. Any other suitable number may
be substituted for the predetermined number 20. Reducing the number
will increase the speed at which the tire monitor positioning is
learned by the system, but may increase the likelihood of incorrect
tire monitor position learning.
[0085] According to the second criterion of the illustrated
embodiment, the counter for the front RF detector must be larger
than the counter for the rear RF detector for two different tire
identifiers out of the four. According to the third criterion, it
is determined if the the frame counter for the rear RF detector
stores a value larger than the front RF detector frame counter for
the two remaining tire identifiers in the list. If these criteria
are not fulfilled using the tire identifiers in the list, control
returns to the block 504 to await receipt of additional frame of
data.
[0086] If these three criteria are fulfilled, however, at block
514, two tire identifiers are selected from the list for the front
axle of the vehicle, according to the second criterion above, and
two tire identifiers are selected from the list for the rear axle,
according to the third criterion above. Thus, at block 518, the
method has chosen four tire identifiers with a total RF frame
counter value higher than 20 and has distinguished the selected
tire identifiers between the front of the vehicle and the rear of
the vehicle by using the front frame counter value and rear frame
counter value. For example, using the values shown in the example
list above, the tire identifiers corresponding to the tire monitors
positioned at the front of a vehicle are tire identifiers id1 and
id2. The tire identifiers corresponding to tire monitors positioned
at the rear of the vehicle are id3 and id4.
[0087] Beginning at block 516, the method identifies the right and
left tire monitor for each axle. First it is determined if, among
the identified tire identifiers from the list for each of the front
and rear axles, one RF detector counter value has a higher frame
counter value than the other. If not, the method cannot distinguish
the two tire monitors on the axle. Control returns to block 504 to
await receipt of additional frames of data. If the criterion of
block 516 is met, at block 518 the tire indicator with the higher
RF detector frame counter value is selected to be on the same side
of the vehicle as the RF detector for that end of the vehicle.
Thus, in FIG. 4, among the front wheels 404, 406, the tire
identifier associated with the larger valued RF detector counter is
selected to correspond to tire monitor 426. Similarly, the tire
identifier having the lower valued RF detector counter value is
selected to be associated with the tire monitor 424. Alternatively,
if, as is suggested in FIG. 5, those RF detectors 414 and 416 are
positioned on the left side of the vehicle 400, then of the tires
of tire identifier selected at block 514, the larger valued RF
detector frame counter is associated with the left-hand side tire
monitor for both axles. In the illustration of FIG. 4, if the RF
detector 414 were instead mounted on the left-hand side of the
vehicle 400, the larger valued tire identifier would be selected to
be associated with tire monitor 424 and the larger valued RF
detector frame counter would be selected to be associated with tire
monitor 428. Using the example list of data above, and assuming
that both tire monitors are on the left-hand side of the vehicle,
the method would select id1 for the left front tire monitor and id2
for the right front tire monitor. Similarly, the method would
select id3 for the left rear tire monitor and id4 for the right
rear tire monitor.
[0088] At block 520, the four selected tire identifiers are stored
in non-volatile memory such as the E.sup.2PROM or other persistent
memory described above. During subsequent operation of the tire
monitor system, as new frames of tire data are received, the tire
identification information contained in the frame will be compared
with one of the selected in store for tire identifiers. If there is
a match, the tire pressure information or other tire data contained
in the frame will be used to update the current tire pressure
information. At block 522, the learn routine illustrated in FIG. 5
is exited and the method of FIG. 5 terminates.
[0089] FIG. 6 illustrates a method for the remote tire monitor
system to learn the positioning of tire monitors on a vehicle
during a normal driving operation. The method begins at block 602,
which is accessed after determining at block 502 (FIG. 5) that tire
monitor identifiers have already been stored in the persistent
memory of the system.
[0090] At block 602, the tire monitor values stored in the
persistent memory are inserted into the list or array in working
memory. The Total RF Frame Counter, the front RF detector counter
value (for identifiers which were in the front) and the rear RF
detector counter value (for identifierswhich were in the rear) for
each of these array entries is preloaded with a predetermined
value, such as 5. Storing preloaded values such as this gives a
weighting to the tire identifiers already stored in the persistent
memory and copied into the working memory array. The benefit of
weighting the preloaded tire monitor values in the array in this
manner is to reduce the likelihood that a tire monitor on an
adjacent vehicle will be detected and selected as one of the four
tire monitors of the vehicle. This could occur, for example, if
more than one vehicle with comparable systems are parked adjacent
each other, such as the end of an assembly line or in another
location. Further, weighting the preloaded tire monitor values
reduces the time required for the learn process so that reliable
information can be given to the driver sooner. This process happens
every time the vehicle is started and a new journey is begun.
[0091] At block 604, it is determined if a frame of data has been
received. If not, control remains in a loop including block 604
until a frame of data is received. Once a frame of data has been
received, control proceeds to block 606.
[0092] At block 606 it is determined if the tire monitor identifier
contained in the received frame is already stored in the persistent
memory or E.sup.2PROM. If not, at block 608 the received tire
monitor identifier is added to the working list of tire identifiers
in working memory. Control proceeds to block 610.
[0093] At block 610, the relevant wheel position counters are
incremented. Operation here is similar to the operation at block
510, FIG. 5. The working list of data includes columns for each of
the front and rear RF detector counters and a total RF frame
counter. At block 610, the total RF frame counter corresponding to
the received tire identifier is incremented. Also at block 610, the
counter corresponding to the front or rear RF detector is
incremented, depending on which RF detector sensed or detected the
transmission from the transmitting tire monitor.
[0094] At block 612, three criteria are tested to determine if
sufficient frames of data have been received to reliably
distinguish front from rear tire monitor positions. Operation of
block 612 is similar to the operation of block 512, FIG. 5. At
block 614, two tire identifiers are selected to correspond to the
front end of the vehicle and two tire identifiers are selected to
correspond to the rear end of the vehicle. At block 612, if all
three criteria are not fulfilled, control returns to block 604 to
await the receipt of additional frames of data.
[0095] At block 616, it is determined if, for each of the front and
rear sets of tire monitors, one tire monitor has a higher RF
detector counter value. If not, control returns to block 604 to
await the receipt of additional data. If so, at block 618, the
front and rear selected tire monitor pairs are each sorted among
right and left tire monitors, selecting a left front, right front,
left rear and right rear tire monitor. At block 620, the four tire
monitor identifiers are stored in non-volatile or persistent
memory, along with position information for the tire monitor. The
learn routine of FIG. 6 is then exited at 622.
[0096] From the foregoing, it can be seen that the present
embodiments provide a method and apparatus which automatically
conveys wheel position and data to a receiver in a vehicle. Even
after changes in tire position due to tire rotation or replacement
of a tire, the system automatically re-learns the position of the
tires on the vehicle. No external actuation is required.
Interference and cross talk are minimized by locating RF detectors
in close proximity to the tire monitors. By sharing one RF detector
between the front wheels and one RF detector between the rear
wheels, the required number of RF detectors is reduced along with
the required cabling and the concomitant cost, weight and
difficulty of installation of the system. Further, the system
provides automatic learn capability for learning and updating the
identities of tire monitors on the vehicle without manual
intervention.
[0097] While a particular embodiment of the present invention has
been shown and described, modifications may be made. For example,
while the exemplary embodiment counts received transmissions from
tire monitors of the system, other embodiments may use alternate
methods or detect other signal parameters to identify tire monitor
positions in the system. Also, while the two learn methods of FIGS.
5 and 6 are generally similarly for both the learn method in the
production line and the learn method during normal driving, other
method steps or test criteria may be substituted to change the two
methods, accounting for the differing environments in which each
method is practiced. It is therefore intended in the appended
claims to cover all such changes and modifications which fall
within the true spirit and scope of the invention.
* * * * *