(12) United States Patent
`(10) Patent N0.:
`US 6,486,773 B1
`
`Bailie et al.
`(45) Date of Patent:
`Nov. 26, 2002
`
`U5006486773B1
`
`(54) METHOD FOR COMMUNICATING DATA IN
`A REMOTE TIRE PRESSURE MONITORING
`SYSTEM
`
`(75)
`
`.
`-
`-
`-
`.
`Inventors 3'3“ Ami/flew 111mg Balhe’lgeus (IE),
`em")
`“rp 3"
`angor (
`)
`(73) Assignee: Schrader-Bridgeport International,
`Inc., Deerfield, IL (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`ginseng ifsixéentded) (dr adjusted under 35
`’
`’
`’
`( )
`y
`ays.
`(21) A l N 09/245 577
`pp .
`0.:
`.
`’
`(22)
`Filed:
`Feb. 5, 1999
`
`(60)
`
`Related US. Application Data
`Provisional application No. 60/099,820, filed on Sep. 10,
`1998-
`(51)
`Int. Cl.7 ................................................ B60C 23/00
`(52) US. Cl.
`........................ 340/445, 340/442, 340/447
`(58) Field of Search ................................. 340/442, 443,
`340/444 445 446 447 448 10.2. 73/1462
`’
`’
`’
`’
`’
`’
`’
`.
`1463, 146.4, 146.5, 370/448
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`2/1979 Lake .......................... 340/347
`4,142,184 A *
`7/1985 Nishimura et al.
`4,529,961 A
`9/1986 Uzzo
`4,609,905 A
`
`4/1992 Williams
`5,109,213 A
`2/1994 Fiorletta
`5,289,160 A
`2/1997 Robinson, III .............. 340/442
`5,600,301 A *
`8/1997 Geschke et al.
`5,661,651 A
`5,963,128 A * 10/1999 McClelland ................ 340/447
`5,969,595 A * 10/1999 Schipper et al.
`.
`..... 340/426
`
`5,999,091 A * 12/1999 Wortham ............. 340/431
`*
`
`
`203333 2 , 13:33?) 2:331?“III 3743/1691
`’
`’
`* cited b
`examiner
`
`y
`Primary Examiner—Nina Tong
`(74) Attorney, Agent, or Firm—Brinks Hofer Gilson &
`Lione
`(57)
`
`ABSTRACT
`
`Amethod and apparatus for communicating data in a remote
`tire pressure monitoring system (10) Which includes a plu-
`rality of transmitters (12) associated with tires (T(1), T(2),
`T(3), and T(4)) of a vehicle (V) and a receiver (14) in radio
`communication with the plurality of transmitters. At each
`W9 if” is C911?Cted(:2)> the data beinggepresemame of a
`tire C aracteristic, SH? .25.an pressure.
`ata representative
`of the tire characteristic is transmitted (86). After a time
`delay (94, 96) next data are transmitted (98) until a prede-
`.
`.
`termined number of data words have been transmitted. The
`
`time delay foreach respective data word is defined accord-
`ing to a repeating pattern common to the plurality of tires so
`that data words are transmitted during a plurality of aperi-
`odic time Windows.
`
`26 Claims, 3 Drawing Sheets
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`1 WORD OR FRAME
`
`
`=o.15 sec
`26
`28
`SWIDTH= 24.7ms
`
`
`24
`68664444
`
`
`
`
`
`
`
`
`
`
`
`
`
`.
`20‘.“
`6 WORDS (1 BLOCK)
`k
`)1
`
`
`3o
`3
`3453525525
`
`22
`
`
`
`
`
`
`
`
`
`
`42
`l
`I
`
`.
`i
`8 WORDS (i BLOCK)
`h
`>1
`
`
`
`44636644
`
`SCHRADER
`
`EXH. 1006
`
`Page 1006-l
`
`Page 1006-1
`
`

`

`US. Patent
`
`Nov. 26, 2002
`
`Sheet 1 0f3
`
`US 6,486,773 B1
`
`RF C3RCUIT
`
`Page 1006-2
`
`Page 1006-2
`
`

`

`US. Patent
`
`Nov. 26, 2002
`
`Sheet 2 0f3
`
`US 6,486,773 B1
`
`1 WORD OR FRAME
`
`G X 257145
`
`26
`
`28
`
`S/VIDTH = 24-7m5 é86é4444
`
`36
`
`20 .
`
`a WORDs (I BLOCK)
`M
`j ,
`
`8X25ms
`30
`3'2 34=o.2 55c
`
`
`
`. 44G8éé44
`
`
`8 WORDS (1 BLOCK)
`.
`
`’2
`
`WORD STRUCTURE
`
`START
`
`FUNCTION
`
`24 BIT ID
`8 BIT PRESSURE
`2 BIT CHECK SUM
`
`
`521)-
`
`50
`I
`I
`I
`I
`I
`4 BITS IBIT SBITB IBIT
`
`34 BITS
`
`M
`
`I
`
`’V
`
`45 BITS = 24.7ms
`
`QC»? 3
`BIT STRUCTURE
`I
`l o: BID WIDTH TOLERANCE +
`
`O/us, ~50/us
`
`i
`
`.
`.
`.
`rah—H
`
`1811/25 344.1/15
`
`‘I BID WIDTH TOLERANCE +
`021.5. — 50,69
`
`54i
`
`c
`
`.
`.
`.
`l-+—>i~<—>-|
`366.1/us 183.1/45
`BID WIDTH =547.2,us (+/— 1%)
`DATA RATE=1.8208 KBITs/s
`
`Page 1006-3
`
`Page 1006-3
`
`

`

`US. Patent
`
`Nov. 26, 2002
`
`Sheet 3 0f3
`
`US 6,486,773 B1
`
`82
`
`92
`
`)7
`
`90
`
`TRANSMYT DATA
`
`68664444
`
`SET 1ST DELAY
`
`
`
`8C
`
`88
`
`DELAY
`
`ELAPSED
` NO
`’2
`
`706
`
` 1ST
`
`Q
` fig/5
`
`702
`
`
`
`
`NEXT
`DELAY
`
`
`ELAPSED
`
`Page 1006-4
`
`Page 1006-4
`
`

`

`US 6,486,773 B1
`
`1
`METHOD FOR COMMUNICATING DATA IN
`A REMOTE TIRE PRESSURE MONITORING
`SYSTEM
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application claims priority of US. provisional appli-
`cation serial No. 60/099,820, filed Sep. 10, 1998.
`
`FIELD OF THE INVENTION
`
`The present invention relates to a method for communi-
`cating data in a remote tire pressure monitoring system.
`
`BACKGROUND
`
`Remote tire pressure monitoring systems have been
`developed using radio technology for providing centralized
`tire pressure information to an operator of a vehicle. Such
`systems typically include a plurality of sending units or
`transmitters associated with the tires of a vehicle, such as an
`automobile, truck or other wheeled vehicle along with a
`receiving unit. The transmitters measure a tire characteristic
`such as tire air pressure, and communicate data correspond-
`ing to the tire characteristic to the receiver. The receiver
`takes some action in response to the data, such as providing
`an alarm or providing a display indicative of the tire
`characteristic, for the operator of the vehicle.
`One problem evident in such a system is clashing of data
`at the receiver. If two transmitters transmit data at the same
`time, a clash can occur, in which case the receiver is unable
`to reliably decode the two transmissions. Any overlap of two
`transmissions from sending units can prevent reception of
`data from both sending units.
`One known solution involves interrupting transmission of
`data during selected repeating time periods at each trans-
`mitter. The total transmission time is divided into a number
`
`for
`of sections, such as ten. During selected sections,
`example,
`two of the ten,
`transmission is suspended to
`provide a quiet time when data from other sending units may
`be transmitted and received successfully. If the quiet times
`of three of four sending units align during a time when the
`fourth sending unit is transmitting, no clash will occur. If
`two transmissions from the same sending unit are decoded
`and are identical, the data is considered valid and reliable.
`While this technique has been acceptable, it would be
`advantageous to further limit clashing to more reliably and
`more quickly communicate tire characteristic information to
`the vehicle operator. Accordingly, there is a need for an
`improved method and apparatus for transmitting data in a
`remote tire pressure monitoring system which reduces clash-
`ing of data.
`
`SUMMARY
`
`The present invention is directed to a method for trans-
`mitting data in a remote tire pressure monitoring system.
`One embodiment of the system includes transmitters located
`at each tire of a vehicle and a receiver mounted on the
`vehicle.
`
`By way of introduction, the method includes collecting
`data on a tire characteristic at tires of a vehicle. The data are
`
`formatted and transmitted by the transmitter according to a
`predefined protocol. In one embodiment, each transmitter
`sends the data during a sequence of aperiodic time windows.
`Because the time windows are aperiodic, the likelihood of
`simultaneous or overlapping transmission by two or more
`transmitters is reduced. In another embodiment, each trans-
`
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`2
`mitter waits a variable time delay before beginning its
`transmission of data. Because the transmitters begin trans-
`mitting at differing times,
`the likelihood of overlapping
`transmission by two or more transmitters is reduced.
`The foregoing description of the present invention 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 SEVERAL VIEWS OF
`THE DRAWINGS
`
`FIG. 1 is a block diagram of a remote tire pressure
`monitoring system;
`FIG. 2 is a timing diagram illustrating data transmission
`by the transmitter of FIG. 2;
`FIG. 3 is a series of timing diagrams showing an example
`of word and bit structure for data transmitted in accordance
`
`with the timing diagram of FIG. 2;
`FIG. 4 is a block diagram of a transmitter for use in the
`remote tire pressure monitoring system of FIG. 1; and
`FIG. 5 is a flow diagram illustrating a method for oper-
`ating the transmitter of FIG. 2.
`
`DETAILED DESCRIPTION OF THE
`PRESENTLY PREFERRED
`
`EMBODIMENTS
`
`Turning now to the drawings, FIG. 1 shows a block
`diagram of a vehicle V that includes in this example four
`tires. The vehicle V includes a remote tire pressure moni-
`toring system 10 that, in this example, includes four sending
`units or transmitters 12 and a receiving unit 14. Each of the
`transmitters 12 includes a battery powered, radio frequency
`(RF)
`transmitter that periodically transmits RF signals
`indicative of pressure or other tire characteristic of the
`associated tire. In this example, the tires are labelled T(1),
`T(2), T(3), T(4), and the associated tire pressures are iden-
`tified as P(l), P(2), P(3), P(4). Structure and operation of the
`transmitters 12 will be described in further detail in con-
`
`nection with FIG. 4. The receiving unit 14 receives RF
`signals from the transmitters 12 and provides a warning to
`the operator of the vehicle V when the indicated tire pressure
`of any of the tires is outside a predetermined range.
`FIG. 2 is a timing diagram illustrating a method for
`transmitting data in a remote tire pressure monitoring
`system, such as the system 10 illustrated in FIG. 1. FIG. 2
`includes two waveforms,
`including a first waveform 20
`illustrating data transmission from a first sending unit or
`transmitter of the remote tire pressure monitoring system
`and a second waveform 22 illustrating data transmission
`from a second transmitter of the remote tire pressure moni-
`toring system. FIG. 2 illustrates one block or frame of
`transmitted data. Each block or frame includes transmission
`
`of eight words of data during eight respective time windows.
`Blocks are preferably repeated at a repetition rate or update
`frequency. The update frequency may be selected to be on
`the order of seconds, minutes or hours, or any other suitable
`rate. Also, as will be discussed below, the update frequency
`may be varied depending on the mode of operation of the tire
`including the transmitter, such as stationary or rolling.
`In the illustrated embodiment, data representative of a tire
`characteristic, such as tire pressure data, are transmitted in a
`pattern represented by the waveforms of FIG. 2. Preferably,
`identical data words are transmitted during sequential time
`windows. Thus, the first transmitter transmits a data word
`
`Page 1006-5
`
`Page 1006-5
`
`

`

`US 6,486,773 B1
`
`3
`during a time window 24 of the waveform 20, retransmits
`the data word during a subsequent time window 26, retrans-
`mits the data word during a subsequent time window 28, etc.
`Similarly,
`the second transmitter transmits a data word
`during a first time window 30, retransmits the data word
`during a second time window 32, retransmits the data word
`during a third time window 34, etc. In this manner, data are
`repeatedly transmitted by each of the sending units or
`transmitters in the system to increase the likelihood that the
`receiver will receive and decode the data without clashing.
`During each time window, a transmitter transmits a data
`word during a transmit time, when the transmitter actively
`transmits data, followed by a variable duration silent time,
`when the first transmitter does not transmit. This continues
`
`until a predetermined number of data words have been
`transmitted. In the illustrated example,
`the transmit time
`during all time windows is uniformly 24.7 ms. This time is
`determined by the composition and duration of the trans-
`mitted word, which will be described in further detail below
`in conjunction with FIG. 3. Other word composition and
`timing may be used as well. For the waveform 20, the time
`window 24 includes a transmit time 36. The reminder of the
`
`time window 24 is silent time. Similarly, the time window 26
`includes a transmit time 38 followed by a silent time until
`the start of a transmit time 40 of the time window 28. For the
`second waveform 22, the time window 30 includes a trans-
`mit time 42 followed by a silent time. The next time window
`32 includes a transmit time 44 followed by a silent time and
`the time window 34 includes a transmit time 46 followed by
`a silent time. The reminder of the time windows of both the
`
`waveform 20 and the waveform 22, used by the first
`transmitter and the second transmitter in the remote tire
`
`respectively, are structured
`
`pressure monitoring system,
`similarly.
`As is illustrated in FIG. 2, time windows for data trans-
`mission from each sending unit are aperiodic. While the time
`windows occur sequentially, their spacing in time is not
`defined by a regular periodicity. Rather, the start of succes-
`sive time windows is timed in response to a predetermined
`duration code. The predetermined duration code used to
`define the waveform 20 is illustrated in FIG. 2 adjacent to
`the waveform 20. The code used in this example is
`68664444. Similarly, the predetermined duration code used
`to define the waveform 22 is illustrated in FIG. 2 next to the
`waveform 22. This code is 44686644. Each transmitter
`
`stores a local copy of this code so that the code is common
`to all tires of the vehicle.
`
`The timing of each time window is measured using the
`predetermined duration code. For example, referring to
`waveform 20 of FIG. 2, the first time window 24 has a
`duration of 0.15 seconds. This duration is set by multiplying
`the first element of the predetermined duration code, 6, by a
`time unit, in this example 25 ms. Any other suitable time unit
`may be chosen. The subsequent
`time window 26 has a
`duration of a 8x25 ms=0.2 seconds. Similarly, the next time
`window 28 has a duration 6x25 ms=0.15 seconds. Thus, the
`start of successive time windows is timed in response to the
`predetermined duration code. Since the transmit time of
`each time window has a uniform length, 24.7 ms in this
`example, the duration of the silent time is similarly timed in
`response to the predetermined duration code.
`In the illustrated embodiment, the predetermined duration
`code is common to all the transmitters in the remote tire
`
`pressure monitoring system. However, each transmitter in
`the system is set to begin at a different location in the code.
`Thus,
`the first transmitter having a timing diagram illus
`
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`35
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`40
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`45
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`50
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`60
`
`65
`
`4
`trated as waveform 20 begins operating using the code
`686 .
`.
`. for timing the transmission time windows. The
`second transmitter having a timing diagram illustrated by
`waveform 22 begins by using the code 446 .
`.
`. for timing
`transmission time windows. Over multiple repetitions of the
`code,
`the transmissions from the transmitters follow the
`same pattern. However, because of use of different starting
`points in the code at each transmitter, the transmissions from
`any plurality of transmitters will not be synchronized, reduc-
`ing the likelihood of clashing of those transmissions at the
`receiver.
`the same data word or
`In the illustrated embodiment,
`words are transmitted during each time window. In alterna-
`tive embodiments, however, data may be updated,
`for
`example by taking an additional tire pressure measurement.
`Updated data are then transmitted in subsequent data words,
`using the predetermined duration code for timing the time
`windows of transmission. Thus, after data representative of
`a tire characteristic have been collected, a data word is
`transmitted in response to the data during the active time of
`the first time window. After a time delay, which is defined at
`least in part by a repeating pattern such as the predetermined
`duration code, a next data word is transmitted at the begin-
`ning of the subsequent time window. The steps of transmit-
`ting a data word and, after a time delay, transmitting a next
`data word are repeated for a predetermined number of data
`words, such as eight data words. The time delay for each
`respective data word is defined according to the repeating
`pattern. As noted above, the repeating pattern is preferably
`common to the plurality of tires by using the same code at
`the different tires. However, a different pattern may be used.
`The duration code or repeating pattern illustrated in the
`drawing has been determined by simulation to be beneficial
`at reducing clashing of data at a receiver in a remote tire
`pressure monitoring system. However, other patterns may be
`used for transmitting data words responsive to collective
`data during a plurality of aperiodic time windows.
`FIG. 3 illustrates exemplary word and bit formatting for
`use in the data transmission technique illustrated in FIG. 2.
`In FIG. 3, a waveform 50 shows an exemplary word 52
`which consists of 45 bits of information. The word 52
`includes a four bit start code followed by a single bit, five
`bits defining a function code, again followed by a single bit
`followed by 34 additional data bits. The 34 data bits are
`distributed between a 24 bit unique identification code (ID)
`and 8 bits representative of a tire characteristic such as air
`pressure measured by the sending unit which transmits the
`word. The 24-bit unique identification code is used to
`identify the tire associated with the reported tire character-
`istic. Also, a two-bit check sum is included to verify reliable
`reception of the word.
`Also in FIG. 3, a waveform 54 and a waveform 56
`illustrate the structure of bits defining a logical 0 and a
`logical 1, respectively. The illustrated embodiment uses
`pulse width modulation (PWM) to transmit data. Exemplary
`bit width and data rate details are provided in FIG. 3 for one
`embodiment of the present invention.
`It should be noted that the word structure and bit structure
`
`illustrated in FIG. 3 are exemplary only and are not required
`for successful operation of a system employing the present
`invention. Alternative embodiments may be employed suc-
`cessfully. For example, rather than employing a pulse width
`modulation protocol, a Manchester coding protocol may be
`used for reliable transmission of data. Such alternative
`
`embodiments may be chosen to provide a faster data com-
`munication rate or reduced power consumption in the send-
`ing unit transmitting the data.
`FIG. 4 shows a block diagram of a sending unit for a
`transmitter 12 for use in the remote tire pressure monitoring
`
`Page 1006-6
`
`Page 1006-6
`
`

`

`US 6,486,773 B1
`
`5
`system 10 of FIG. 1. The transmitter 12 includes a pressure
`sensor 60, a controller 62, a roll switch 64, a learn switch 66,
`a radio frequency (RF) circuit 68 and an antenna 69, a clock
`70, and a battery 72. The components of the transmitter 12
`are contained within a housing 74. The transmitter is
`intended to be mounted on or within a tire of a vehicle for
`detecting a characteristic of the tire and transmitting data
`representative of the characteristic to a receiver such as the
`receiving unit 14 of the remote tire pressure monitor system
`10 of FIG. 1. In the illustrated embodiment, the tire char-
`acteristic is air pressure of the tire. However, other tire
`characteristics may be measured, such as tire temperature,
`number of rotations of the tire, etc.
`The pressure sensor 60 forms a sensor for detecting an
`operating condition of the tire associated with the transmitter
`12 and producing an indication at an output 76. In the
`illustrated embodiment, the pressure sensor 60 is a pressure
`transducer which detects air pressure of the tire and pro-
`duces either an analog signal or digital data representative of
`the tire pressure at the output 76.
`The controller 62 controls operation of the transmitter 12.
`In the illustrated embodiment, the controller 62 is imple-
`mented as an application specific integrated circuit (ASIC).
`In alternative embodiments, the controller 62 may be imple-
`mented as a general purpose microprocessor or hard wired
`circuitry. The ASIC implementation provides advantages of
`reduced size, weight, cost and power drain, which are all
`important design considerations for the transmitter 12.
`The controller includes various circuitry for receiving
`input signals, operating on the input signals and providing
`output signals. In particular, the controller 62 includes a data
`receiving circuit configured to receive the indication of the
`tire pressure from the output 76 of the pressure sensor 60.
`The data receiving circuit may be, for example, an analog to
`digital converter. Further, the controller includes a control
`circuit which formats data words in response to the indica-
`tion for communication to a remote receiver during a
`plurality of aperiodic time windows, for example as is
`illustrated in FIG. 2. Still further, the controller 62 includes
`a memory 78 coupled to the control circuit of the controller
`for storing data.
`The RF circuit 68 is coupled to the controller 62 for RF
`transmission of data words to a remote receiver. This may be
`accomplished by any suitable method, for example modu-
`lation by the data words of a carrier signal, with the
`modulated carrier being impressed upon the antenna 69 for
`RF transmission of the data.
`
`The clock 70 provides a timing circuit coupled to the
`controller 62 to establish reference timing for the transmitter
`12. The controller 62 is responsive to the reference timing
`for timing operation of the transmitter 12. For example, the
`controller 62 formats data words for transmission during
`aperiodic time windows to a remote receiver. The controller
`62 is responsive to reference timing to space the aperiodic
`time windows in time according to a repeating pattern. In the
`illustrated example, the repeating pattern is stored in the
`memory 78 and is,
`for example,
`the repeating pattern
`68664444 .
`.
`. illustrated in FIG. 2. Thus, in one exemplary
`embodiment, the controller 62 selects an element of the code
`which forms the repeating pattern from the memory 78. The
`controller 62 multiplies a time unit, such as a 25 ms, by the
`selected element, and, in response to reference timing estab-
`lished by the clock 70, times the start of a subsequent time
`window. In this manner, the transmitter 12 is configured to
`transmit a data word during a time window, wait a prede-
`termined variable time defined at least in part by the repeat-
`ing pattern, and transmit a next data word during a next time
`window.
`
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`30
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`35
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`60
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`65
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`6
`As noted, the codes which form the repeating pattern are
`preferably stored in the memory 78. Alternatively, the codes
`may be calculated or determined in any suitable manner. In
`the preferred embodiment,
`the codes are stored in the
`memory 78 at the time of manufacture of the transmitter 12.
`Further, the starting point in the code used by the controller
`62 when transmitting first data words is set randomly. This
`can be done by storing the code with a random starting
`location or by randomly selecting the starting point in the
`code at the controller 62.
`The roll switch 64 detects a rotational characteristic of a
`
`tire associated with the transmitter 12, such as rolling at a
`specified speed, and provides an indication when the rota-
`tional characteristic exceeds a predetermined threshold. In
`the illustrated embodiment, the roll switch 64 includes a reed
`switch which closes at a specified g force (i.e., a multiple of
`the acceleration due to gravity). In response to closing of the
`roll switch 64, the controller 62 responds by, for example,
`increasing the sampling and transmission rates of the trans-
`mitter 12. For example, in one embodiment, when a vehicle
`employing the transmitter 12 begins moving at a speed
`exceeding 30 km/h, the roll switch 64 closes. In response,
`the controller 62 reads the indication of air pressure pro-
`vided by the pressure sensor 60 at an increased rate and
`closes the RF circuit 68 to transmit data words indicative of
`
`the air pressure also at an increased rate. In this example,
`when the vehicle is stationary or moving at a speed below
`the threshold of 30 km/h, the sample rate as determined by
`the controller 62 is approximately one sample every 15
`minutes. The transmission rate, also referred to as the update
`rate or update frequency, is approximately one transmission
`of eight identical data words every sixty minutes. After the
`roll switch 64 closes, the sample rate is increased by the
`controller 62 to one sample per 10 seconds and the trans-
`mission rate is increased to one transmission every one
`minute, increasing the update frequency. Thus the illustrated
`transmitter 12 provides an increased pressure monitoring
`mode with more frequent sampling and transmission when
`the vehicle is in motion. After the vehicle is again stationary
`and the roll switch 64 opens, the controller 62 reduces the
`sample and transmission rate.
`In one embodiment, the roll switch 64 closes at a specified
`g force value which is selected from a range of values. In one
`example, the range of g force values varies from 6.1 to 12.2
`times the acceleration due to gravity. The selected g force
`value for a particular roll switch 64 is set randomly during
`manufacture of the transmitter 12. The roll switches as
`
`supplied have a natural spread of switching points. In this
`manner, each of the respective transmitters 12 associated
`with the tire of a vehicle will employ differing g force values
`for activating the increased pressure monitoring mode. Since
`this mode corresponds to an increase in RF transmissions by
`the transmitter 12 as well as all other transmitters used by the
`vehicle, this mode will correspond to an increased likelihood
`of clashing at the receiver. By spreading the a range of g
`force values at which the transmitters switch to the increased
`
`the likelihood of clashing or
`pressure monitoring mode,
`word collision at the receiver is decreased.
`
`Referring now to FIG. 5 it shows a flow diagram illus-
`trating a method for transmitting data in a remote tire
`pressure monitoring system. The method begins at step 80.
`At step 82, data representative of a characteristic of a tire
`are collected. For example, pneumatic air pressure, tempera-
`ture or other physical characteristic of the tire may be
`measured. At step 84, which is shown in dashed lines to
`indicate it is an optional step, the method includes waiting
`a variable delay time before step 86,
`transmitting data.
`
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`Page 1006-7
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`US 6,486,773 B1
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`7
`Preferably, the variable delay time is different from variable
`delay time used by other transmitters in the remote tire
`pressure monitoring system. In this manner, the likelihood of
`word collision or clashing upon reception at a receiver in the
`system is reduced. At step 86, data are transmitted using any
`suitable data transmission technique.
`In the
`At step 88, a first delay time is determined.
`illustrated embodiment,
`the first delay time is illustrated
`using a first data element of a repeating pattern contained in
`a memory 90 or other storage location. Apointer 92 points
`to the current element of the repeating pattern to be used for
`determining the delay time. In the illustrated embodiment,
`the repeating pattern includes a plurality of integer numbers,
`such as the exemplary pattern 68664444. One integer num-
`ber of a plurality of integer numbers is selected in sequence
`for combination with a time unit, such as a standard time
`duration. Upon exhaustion of the sequence,
`the pointer
`returns to a first element of the repeating pattern and the
`sequence is repeated. In other embodiments, other tech-
`niques may be used for establishing the repeating pattern.
`After determining the first delay time, the method, at step
`94 and step 96 enters a loop to await elapse of the first delay
`time. If the first delay time has elapsed, the method proceeds
`to step 98 where next data words are transmitted. Transmis-
`sion may be by any suitable method for reliable reception of
`the data words.
`
`At step 100, a next delay time is determined using a next
`data element of the repeating pattern stored in the memory
`90. For example, the pointer 92 is incremented to point to the
`next data element. After determining the next delay time, the
`method enters a loop including step 102 and step 104 to
`await the duration of the next delay time. After the next
`delay time has elapsed, step 104, next data words are
`transmitted, at step 106. At step 108, the method determines
`if all data words designated for transmission have been sent.
`For example, a predetermined number of data words, such as
`8 data words, may be transmitted together as a block. If all
`data words have not yet been sent, control returns to step 100
`to set a next delay time using the predetermined pattern
`contained in the memory 90. Instead if all data words have
`been sent the method ends at step 110.
`As can be seen from the foregoing, the preferred embodi-
`ment provides a method and apparatus for transmitting data
`in a remote tire pressure monitoring system. The system
`includes a plurality of transmitters associated with tires of a
`vehicle and a receiver in radio communication with the
`
`plurality of transmitters. At each of the transmitters, data
`representative of a tire characteristic is collected and for-
`matted for transmission to the receiver. Each transmitter
`
`transmits data words during a plurality of aperiodic time
`windows. The aperiodic time windows tend to randomize
`the time of transmission of the data words from each of the
`
`respective transmitters. This reduces the likelihood of coin-
`cident reception of data words at the receiver and therefore
`improves the likelihood of accurate, reliable reception of
`data at the receiver.
`
`While a particular embodiment of the present invention
`has been shown and described, modifications may be made.
`For example, different tire characteristics may be monitored
`and reported to the receiving unit. Also,
`in another
`modification, instead of varying the duration of the time
`windows of transmission, the silent time when a transmitter
`does not transmit may be varied. It is therefore intended in
`the appended claims to cover all such changes and modifi-
`cations which follow in the true spirit and scope of the
`invention.
`
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`What is claimed is:
`1. A method for transmitting data in a remote tire pressure
`monitoring system, the method comprising the acts of:
`at each tire of a plurality of tires of a vehicle, collecting
`data representative of a tire characteristic; and
`at each respective tire, transmitting data words responsive
`to the data representative of the tire characteristic
`during a plurality of time windows, transmission timing
`of the plurality of timing windows being defined by a
`preassigned, respective different starting point of a
`predetermined, multiple-valued code common to the
`plurality of tires of the vehicle to form a unique code
`for the respective tire.
`2. The method of claim 1 wherein said act of transmitting
`data words comprises the act of transmitting a data word
`during a transmit time followed by a variable duration silent
`time until a predetermined number of data words have been
`transmitted.
`3. The method of claim 2 further comprising the act of
`timing duration of the silent time in response to the unique
`code for the respective tire.
`4. The method of claim 1 her comprising the act of timing
`start of successive time windows in response to the unique
`code for the respective tire.
`5. The method of claim 4 wherein the unique code for the
`respective tire comprises a portion of the predetermined,
`multiple-valued code common to the plurality of tires of the
`vehicle.
`
`6. The method of claim 1 wherein said act of transmitting
`data words comprises transmitting identical data words
`during sequential time windows.
`7. The method of claim 1 further comprising the act of, at
`each tire, waiting a variable time delay after collecting the
`data before transmitting the data words, the variable time
`delay at each tire differing from the variable time delay at
`other respective tires.
`8. The method of claim 1 wherein the acts of collecting
`data and transmitting data word are repeated at an update
`frequency.
`9. The method of claim 8 further comprising the acts of:
`at each tire, detecting a signal indicative of vehicle speed;
`and
`
`when the signal exceeds a threshold, varying the update
`frequency, the threshold at each tire differing from the
`threshold at other respective tires.
`10. The method of claim 1 wherein the data comprise data
`indicative of air pressure of the tire.
`11. A method for transmitting data in a remote tire
`pressure monitoring system, the method comprising the acts
`of:
`
`(a) at each tire of a plurality of tires of a vehicle, collecting
`data representative of a tire characteristic;
`(b) transmitting a data word in response to the data;
`(c) after a time delay, transmitting a next data word; and
`(d) repeating acts (b) and (c) for a predetermined number
`of data words, the time delay for each respective data
`word being defined according to a local copy of a
`repeating pattern common to the plurality of tires, the
`local copy being preassigned to the each tire so that
`transmission at each tire begins at a different location in
`the repe