US006998973B2
`
`(12) United States Patent
`Lefaure
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,998,973 B2
`Feb. 14, 2006
`
`(54) DATA TRANSMISSION METHOD FOR A
`TIRE-PRESSURE MONITORING SYSTEM OF
`A VEHICLE
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`(75)
`
`Inventor: Philippe Lefaure, Montbrun Lauragais
`(FR)
`
`(73) Assignee: Siemens VDO Automotive, Toulouse
`Cedex (FR)
`
`11/1998 Robinson
`5,838,229 A
`6,331,822 B1 * 12/2001 Sato et al.
`............... .. 340/3.22
`6,505,507 B1 *
`1/2003 Imao et al.
`73/146.5
`
`6,700,480 B1 *
`3/2004 Moore . . . . . . . . . . .
`. . . . .. 340/445
`6,885,293 B1 *
`4/2005 Okumura .................. .. 340/448
`
`FOREIGN PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 149 days.
`
`W0
`
`W0 96 15919
`
`5/1996
`
`* cited by examiner
`
`(21) Appl. No.: 10/771,374
`
`(22)
`
`Filed:
`
`Feb. 5, 2004
`
`(65)
`
`Prior Publication Data
`
`US 2004/0155762 A1
`
`Aug. 12, 2004
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 6, 2003
`
`(FR)
`
`................................. .. 03 01386
`
`(51)
`
`Int. Cl.
`B60C 23/00
`
`(2006.01)
`
`(52) U.S. Cl.
`
`.................... .. 340/442; 340/438; 73/146.2
`
`(58) Field of Classification Search .............. .. 340/442,
`340/438, 443, 445, 446, 447, 448; 73/146.2,
`73/146.3, 146.8
`See application file for complete search history.
`
`Primary Examiner—Daryl C Pope
`(74) Attorney, Agent, or Firm—Young & Thompson
`
`(57)
`
`ABSTRACT
`
`A data transmission method for a tire-pressure monitoring
`system (10) of a Vehicle. The data is transmitted by Wheel
`units (12) to a central computer (13) located in the Vehicle.
`The method comprises:
`a data transmission phase in parking mode, over a first
`period; and
`a data transmission phase in running mode, over a second
`period shorter than the first period. The method is
`characterized in that a natural time lag between Various
`internal clocks with which each Wheel unit (12) is
`equipped is used to prevent collisions between trans-
`missions from the Various Wheel units of one and the
`same Vehicle.
`
`12 Claims, 1 Drawing Sheet
`
`
`
`—.QTSn'i':'7l
`
`1 0
`
`SCHRADER
`
`EXH. 1001
`
`Page 1001-l
`
`Page 1001-1
`
`

`
`U.S. Patent
`
`Feb. 14, 2006
`
`US 6,998,973 B2
`
`
`
`--- ..
`
`——>: k-
`._—.§:
`:
`V‘.
`I
`i
`
`3
`
`:<—
`—>:
`'
`:
`E §60ms +Aams
`:
`:
` frame 1
`
`--+:
`:
`5
`:
`
`:e—
`...
`.-
`...
`:< - ._..-.......
`:80ms+A0‘ms
`:
`
`12
`
`10
`
`8
`
`6
`
`sample
`amount
`
`per class
`
`
`
`
`
`
`D“’—K3*~""1A45?-:3rs-L-:.‘.‘.'11.:-Iv...x..~“$9.
`
`
`Page 1001-2
`
`Page 1001-2
`
`

`
`US 6,998,973 B2
`
`1
`DATA TRANSMISSION METHOD FOR A
`TIRE-PRESSURE MONITORING SYSTEM OF
`A VEHICLE
`
`FIELD OF THE INVENTION
`
`invention relates to a data transmission
`The present
`method for a tire-pressure monitoring system of a vehicle.
`More particularly,
`it relates to a method for preventing
`collisions between the data transmitted by the wheel units of
`one and the same vehicle.
`
`BACKGROUND OF THE INVENTION
`
`It is known to equip motor vehicles with tire-pressure
`monitoring systems. These systems generally comprise a
`device fixed to the inside of the tire and called a wheel unit.
`
`This wheel unit measures the pressure inside the tire (and
`also a certain number of other parameters such as, for
`example, the temperature) and transmits the measurements
`made to a central computer located in the vehicle. This
`central computer is responsible for warning the driver of any
`pressure defect in one of the tires. Of course, each wheel unit
`is provided with an identifier so that the data received by the
`central computer not only contains the measurements made
`but also an indication of position of tire (right or left front
`tire, right or left rear tire) in which these measurements have
`been made.
`
`It is also known to transmit the data, measured by the
`suitable sensors located in the wheel units, at different time
`intervals depending on the movement of the vehicle. If the
`vehicle is in parking mode, that is to say at rest or moving
`at very slow speed (for example less than 25 km/h), the
`measurements made by the wheel units are generally trans-
`mitted at relatively long time intervals (of around one hour).
`On the other hand, when the vehicle is in running mode, that
`is to say moving at more than 25 km/h, the same information
`is transmitted to the central processing unit at time intervals
`of around one minute.
`
`As soon as the vehicle is in running mode, each wheel unit
`regularly transmits the measurements made. However, many
`transmission are thus made simultaneously by several wheel
`units of one and the same vehicle. This results in scrambling
`of the messages received by the central processing unit that
`collects the transmissions coming,
`sometimes simulta-
`neously, from the four wheels (or even more in the case of
`heavy goods vehicles). In this case, the data measured can no
`longer be used and the system becomes inoperable.
`To overcome these drawbacks, it is known to time-shift
`the transmission of each wheel unit. These time-shifting
`methods are complex as they require all the wheel units of
`one and the same vehicle to be synchronized. Furthermore,
`this requires complex computations that
`limit
`the time
`intervals available for transmission.
`
`To overcome this problem of collision between data
`transmitted by each wheel unit, it is also possible to ensure
`that the central computer interrogates each of the wheel units
`one by one. However, here again,
`this operating mode
`extends the time required to receive all the data and slows
`down the performance of the tire-pressure monitoring sys-
`tem.
`
`SUMMARY OF THE INVENTION
`
`The object of the present invention is to implement a
`method of transmitting data between a wheel unit and a
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`central computer that avoids collisions between the trans-
`mitted data, while remaining simple, inexpensive and fast.
`For this purpose, the present invention relates to a data
`transmission method for a tire-pressure monitoring system
`of a vehicle, said data being transmitted by wheel units to a
`central computer located in the vehicle, said method com-
`prising:
`a data transmission phase in parking mode, over a first
`period; and
`a data transmission phase in running mode, over a second
`period shorter than the first period; said method being
`characterized in that:
`
`a natural time lag between various internal clocks with
`which each wheel unit is equipped is used to prevent
`collisions between transmissions from the various
`wheel units of one and the same vehicle.
`
`By virtue of this natural time lag, it is possible to prevent
`collisions between transmitted data without employing
`means that are complex, time-consuming and expensive.
`More precisely, the relatively poor precision of the cir-
`cuits producing the internal clock of the wheel unit is put to
`good use in order to automatically time-shift (randomly) the
`transmissions from the wheel units.
`
`Again advantageously, the internal clocks of the wheel
`unit are produced by RC-type oscillating circuits. The pre-
`cision of such oscillators is preferably about 115%.
`Thus, unlike what is usually produced in the wheel unit,
`in which it is general practice to seek to have extremely
`precise internal clocks so as to be able to operate a defined
`time shift between the transmission of the data and thus
`
`prevent collisions, the present invention uses, on the con-
`trary, internal clocks of poor precision, and therefore there
`are less expensive and less difficult to implement in order to
`obtain a similar result.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Other objects, features and advantages of the present
`invention will also become apparent from the description
`that follows, given by way of non-limiting example and with
`reference to the appended drawings in which:
`FIG. 1 is a schematic view of a vehicle fitted with a device
`
`according to the invention;
`FIG. 2 is a schematic view showing an example of frame
`transmission in running mode; and
`FIG. 3 is a diagram showing the range in inter-frame time
`owing to the natural internal time lag of the device used.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`the
`According to the embodiment shown in FIG. 1,
`tire-pressure monitoring system 10 according to the inven-
`tion comprises two main elements, namely:
`a plurality of wheel units 12 mounted in each of the
`wheels 11 of the vehicle; and
`a central computer 13 that receives the data transmitted by
`the wheel units. This central computer is placed in the
`vehicle.
`
`Indicated below is a very brief reminder of how a tire-
`pressure monitoring system operates.
`The wheel units 12, placed in each of the wheels, are
`positioned on the rim inside the wheel. These wheel units are
`provided with suitable sensors, especially with a pressure
`sensor, but also with sensors for measuring temperature,
`acceleration, speed, etc. Each wheel unit has an identifier
`that is specific to it. It regularly transmits data (including the
`
`Page 1001-3
`
`Page 1001-3
`
`

`
`3
`
`4
`
`US 6,998,973 B2
`
`values of the measurements made, but also its identifier) to
`the central computer that receives and processes the data.
`Sometimes, this data has already been preprocessed in the
`wheel unit itself. After processing,
`the central computer
`determines whether it is necessary to inform the driver of a
`defect and, in order to do so, uses the display devices 14
`located on the instrument panel of the vehicle.
`It should be noted (see. FIG. 2) that the messages trans-
`mitted by the wheel units preferably consist of three frames
`having identical data. These frames are each transmitted for
`10 ms. The time interval separating the first and second
`frames is 160 ms+Ao ms. The time interval separating the
`second and third frames is 180 ms+Ao ms. A0 is a value due
`
`to the imprecision of each clock. The value of 0 is 0.25 ms
`(as will be explained later with regard to FIG. 3). The entire
`message (with these three frames) is transmitted every
`minute when the vehicle is moving (for example with a
`speed greater than 25 km/h). It should also be noted that the
`entire message is transmitted during one revolution of the
`vehicle’s wheel, so as to avoid transmission symmetry
`problems.
`Each wheel unit consists in particular of a microcontroller
`whose internal clock consists, according to the present
`invention, of an RC oscillator (a conventional device com-
`prising resistors and capacitors) and of an RF transmitter.
`According to the present invention, it is preferred to use
`RC oscillators whose precision is about 115%.
`Thus, when the microcontroller of the wheel units detects
`that the vehicle is in running mode, it starts to transmit data,
`especially pressure data, every minute. Now, the microcon-
`troller call-up and the transmission sequence are managed
`by means of the internal clock with a precision of about
`115%. This has the consequence of randomly time-shifting
`the transmissions of the first frames of a message, but also
`of the following two frames.
`As FIG. 3 shows, the tolerance of the oscillator follows a
`Gaussian-type distribution law with a standard deviation of
`around 25 ms.
`
`Thus, the transmission sequence of the various messages
`coming from the various wheels makes it possible to avoid
`(or minimize) the risk of a collision between the transmitted
`data, by randomly time-shifting each frame transmission
`from a wheel unit relative to the other wheel units.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`The use of the substantial tolerance possessed by each
`internal microcontroller clock mounted in each wheel unit
`
`45
`
`thus makes it possible to minimize the risk of simulta-
`neously transmitting several information items, without the
`use of complex and/or expensive devices.
`It should be noted that the natural time lag A0 also applies
`to the time interval of one minute (in running mode) and of
`one hour (in parking mode) between each data transmission.
`Of course,
`the present invention is not limited to the
`method of implementation indicated above, rather it encom-
`passes any variant lying within the competence of a person
`skilled in the art. Thus,
`the degree of precision may be
`different from 115%, provided that this automatically intro-
`duces a time lag in the transmissions, thus avoiding any risk
`of a collision. Likewise, the operating mode of the vehicle
`
`50
`
`55
`
`(parking or running) may be determined by a speed of
`movement other than 25 km/h. In particular, the running
`mode may be detected as soon as the ignition has been
`turned on or the engine started, or even as soon as a request
`for gaining access to the inside of the vehicle is indicated.
`What is claimed is:
`
`1. A data transmission method for a tire-pressure moni-
`toring system (10) of a vehicle, said data being transmitted
`by wheel units (12) to a central computer (13) located in the
`vehicle, said method comprising:
`a data transmission phase in parking mode, over a first
`period; and
`a data transmission phase in running mode, over a second
`period shorter than the first period; said method being
`characterized in that:
`
`a natural time lag between various internal clocks with
`which each wheel unit (12) is equipped is used to
`prevent collisions between transmissions from the vari-
`ous wheel units of one and the same vehicle.
`2. The method as claimed in claim 1, characterized in that
`the internal time lag between the various clocks of each
`wheel unit is preferably determined by the precision of an
`RC-type oscillator mounted in each wheel unit.
`3. The method as claimed in claim 2, characterized in that
`RC oscillators having a precision of about 115% are pref-
`erably used.
`4. The method as claimed in claim 1, characterized in that
`each wheel unit transmits several frames for each data item
`to be transmitted.
`5. The method as claimed in claim 4, characterized in that
`three frames are transmitted for each data item to be trans-
`mitted.
`6. The method as claimed in claim 5, characterized in that
`the time interval separating the first and second frames is
`around 60 ms+Ao ms and the time interval separating the
`second and third frames is around 80 ms+Ao ms.
`7. The method as claimed in claim 4, characterized in that
`the frames transmitting the same data item are transmitted
`during a single wheel revolution.
`8. A tire-pressure monitoring system (10) of a vehicle,
`employing the method as claimed in claim 1, said system
`being characterized in that it includes, for each wheel unit
`(12), an internal clock produced by an RC type circuit whose
`precision is about 115%.
`9. The method as claimed in claim 2, characterized in that
`each wheel unit transmits several frames for each data item
`to be transmitted.
`10. The method as claimed in claim 3, characterized in
`that each wheel unit transmits several frames for each data
`item to be transmitted.
`11. The method as claimed in claim 5, characterized in
`that the frames transmitting the same data item are trans-
`mitted during a single wheel revolution.
`12. The method as claimed in claim 6, characterized in
`that the frames transmitting the same data item are trans-
`mitted during a single wheel revolution.
`
`Page 1001-4
`
`Page 1001-4