Method of allocating transmitters of a tire pressure monitoring system to a particular vehicle

A vehicle tire pressure monitoring system includes a pressure sensor, a transmitter, and a transmitting antenna at each of N wheels of the vehicle, and at least one receiving antenna attached to the vehicle, respectively allocated to each transmitting, antenna. The receiving, antenna is connected to an electronic receiving, and analysis system which determines whether a signal belongs to the local vehicle by allocating an identifier characterizing the individual wheel to its transmitter. Emitted signals contain the identifier and are forwarded to the central electronic receiving and analysis system, which records the signal intensities under the signal's identifier, compares the intensities, selects those N transmitter identifiers with the greatest intensities, then stores the N transmitter identifiers as belonging to the vehicle.

BACKGROUND OF THE INVENTION
 Previously-known tire pressure monitoring systems include a pressure
 sensor, transmitter, and transmission antenna, with respective allocated
 receiving antennas and a central electronic analysis system on the vehicle
 body. The problem that arises with tire pressure monitoring systems of
 this kind is unequivocal allocation of the transmitters to the respective
 wheel position. In the past, the problem of position recognition is was
 solved as follows-the transmitters generate a signal divided into four
 segments, consisting of preface, identification signal, measurement
 signal, and conclusion. The central electronic analysis system can
 recognize the position based on the identification signal. Doing so,
 however, first requires first performing an initialization during which
 the respective identification signal, linked to the respective position,
 is stored by the central electronic analysis system. To perform this
 initialization, the system must be switched into a "pairing" mode, and
 each individual transmitter must then be activated once in sequence. The
 system is then switched back into measurement mode until the transmitter
 positions change, e.g. if a wheel is changed. This means, however, that a
 suitably trained person must perform this initialization each time a wheel
 is changed. In some circumstances it is therefore impossible, or possible
 only at the cost of safety, to perform a wheel change at any repair shop
 or at home. Flawless operation of the system cannot be guaranteed due to
 potential operating errors.
 In another known system, the problem is circumvented by recording the data
 for the pressure sensors and the transmission electronics connected to
 them by means of a remote-control element instead of by means of the
 central electronic system. The remote-control element comprises an LCD
 display device which makes it possible to read the tire pressure. To
 determine the tire pressure, the desired information must be interrogated
 at each individual wheel by means of the remote-control element. Although
 this method offers the advantage of an unequivocal allocation of readings,
 it does not allow tire pressure to be checked while driving.
 SUMMARY OF THE INVENTION
 The object of the present invention is therefore to develop a method for
 position recognition which demands no special abilities of even
 inexperienced mechanics or automobile owners when it is necessary, after
 wheels are first mounted and after a wheel change, to recognize, on the
 basis of the signals with different identifiers which are emitted from
 multiple wheels, which signals derive from the vehicle's own wheels. The
 intent is to rule out any failure due to possible operating errors.
 According to the invention, a central electronic analysis system records
 the intensities at which the same transmitter is received at a receiving
 antenna. These values are then compared, multiple successively received
 signals are taken into consideration in order to avoid incorrect
 allocations. An average can then be taken of the multiple signals, or a
 simple count is made of how often the event occurs in which a specific
 antenna most strongly receives a transmitter, i.e. a signal with a
 specific identifier. Based on the average or the greatest number of
 events, the transmitter transmitting with that identifier, or the
 pertinent wheel, is then classified as belonging to the local vehicle, and
 the identifier is stored in the central receiving and electronic analysis
 system as the identifier of a local wheel. The procedure is the same for
 the second-strongest signal, third-strongest signal, etc., until the
 Nth-strongest signal has been identified, N being the number of wheels
 mounted on the vehicle, which can include an onboard spare wheel if it is
 housed so that the signals emitted by it are not too strongly shielded. If
 a spare wheel in the trunk is so strongly shielded that the signals
 emitted by it cannot be received more strongly than the signals proceeding
 from adjacent vehicles, the spare wheel should then not be included in the
 recognition process of the invention.
 If the vehicle has, for example, four wheels, then according to he
 invention the four strongest signals with four different identifiers are
 determined and stored; taking a spare wheel into consideration, there may
 also be five identifiers for the total of five wheels. If additional
 signals are received thereafter, having an identifier which does not match
 any of the stored identifiers, these are not taken into account--or are
 taken into account in subordinate fashion in the tire pressure monitoring
 process.
 If a distinction is to be made between running wheels of a vehicle and one
 or more spare wheels being carried in the vehicle, this is advantageously
 possible by means of the invention.
 Signals which derive from transmitters located on wheels which are rotating
 (running wheels) are received with fluctuating signal levels because the
 location of the transmitter relative to the receiving antenna changes
 cyclically as a result of the wheel rotation. The situation is different
 for onboard spare wheels. When signals emitted from a spare wheel are
 received, they do not exhibit the fluctuations in signal level resulting
 from vehicle motion. This makes it possible to find an additional
 criterion by which to distinguish between signals coming from a spare
 wheel and signals coming from running wheels. If, while the vehicle is in
 motion, a received signal does not exhibit any of the fluctuations in
 signal level caused by wheel rotation, it may be concluded therefrom that
 it derives from an onboard spare wheel and not from a running wheel, even
 if that signal whose level exhibits no motion-related fluctuations is
 received at by the receiving antenna at the greatest intensity. Such a
 signal is either allocated to a spare wheel or is left entirely out of
 consideration (the latter, in particular, if onboard spare wheels are not
 intended to be monitored). This development of the invention has the
 advantage that the risk of erroneous allocations is once again reduced.
 This is true particularly with regard to those running wheels which are
 located at approximately the same distance as, or farther away than, the
 spare wheel, so that the signal emitted from the spare wheel is received
 at approximately the same intensity as, or a higher intensity than the
 signals emitted from a running wheel. The development of the invention
 ensures that an erroneous allocation does not occur even in this
 unfavorable case.
 This method is useful not only when as is usual, a single spare wheel is
 carried on board, but also when multiple replacement wheels are carried.
 When additional wheels with snow tires are carried in the trunk, for
 example, the signals emitted by them cannot disrupt the correct allocation
 of the running wheels to their receiving antennas.
 Another possibility for distinguishing between signals coming from rotating
 wheels and signals coming from replacement wheels involves use of the fact
 that in the initial phase of vehicle motion after motion begins, the tire
 temperature generally rises due to flexing. This is not the case with a
 spare wheel, since its tire is not flexed. If a temperature sensor is
 provided in the tire pressure monitoring system at each wheel in addition
 to the pressure sensor, and if the signal emitted by the transmitter on
 the wheel transfers information not only about tire pressure but also
 about tire temperature, a temperature rise signaled after vehicle motion
 begins can then be evaluated as an indication that the signal derives from
 a rotating wheel and not from a spare wheel.
 It is sufficient if the vehicle has only a single receiving antenna, which
 is housed at a suitable point on the underside of the body or chassis so
 that it can receive signals at sufficient intensity from all the wheels
 attached to the vehicle. It is also possible, however, to allocate a
 separate antenna to each wheel in the latter's vicinity. In this case the
 ranking of the intensity at which the signals are received by the various
 antennas will differ from one antenna to another, since each antenna will
 receive at the greatest intensity that signal which is proceeding from the
 wheel closest to it. The group of the N strongest signals with different
 identifiers will, however, be the same for each of the receiving
 antennas,--only the ranking within the group will differ from one
 receiving antenna to another. To recognize the identifiers possessed by
 the wheels belonging to the local vehicle, it is sufficient to determine
 the N members of the group. If one of the receiving antennas should
 receive most strongly a group of N signals whose identifiers do not
 completely match the N identifiers which the other receiving antennas have
 recorded with the N greatest intensities, then an erroneous measurement
 must be present, which can be corrected by repetition of the measurement
 and analysis. Recognition reliability can therefore be improved by working
 with multiple antennas.
 Since the receiving antenna directly adjacent to a transmitter generally
 receives the signal at greater intensity than the other receiving
 antennas, and since multiple signals are also be utilized for analysis,
 this method not only makes possible recognition of the wheels and their
 identifiers belonging to the local vehicle, but it is also possible to
 recognize which wheel is located at which point on the vehicle.
 Since the method according to the invention operates automatically, there
 can inherently be no problems due to operating errors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The manner in which the position on the vehicle of a wheel with a specific
 identifier can be recognized automatically is described in the PCT patent
 application entitled "Method for allocating transmitters to receiving
 antennas in tire pressure monitoring systems," filed on the same date and
 claiming the priority of German patent applications 195 42 833.1 and 196
 08 478.4, which are hereby incorporated by reference.
 A possible procedure for storing the data obtained from multiple receiving
 antennas and transmitted to the electronic analysis system involves use of
 an allocation matrix, consisting of all the transmitter identifiers and
 receiving antennas. In the course of the allocation process, the value in
 a matrix cell is incremented when the greatest intensity is measured for
 the relevant combination of receiving antenna and transmitter identifier.
 If the tire pressure monitoring system has only a single centrally mounted
 receiving antenna, the matrix is then reduced to a list in which the
 transmitter identifiers of the received signals are entered, and are
 analyzed or weighted in accordance with the received intensity.
 The development of the method according to the invention can be quicker if
 the value of a matrix cell or list place is incremented not by a fixed
 value but by a value weighted in terms of the intensity difference the
 result will be that the matrix cells or list places with the N greatest
 values can be determined more quickly. If a simple count is made of the
 number of events in which a signal with a specific identifier was received
 by a specific antenna at the greatest, second greatest, . . . Nth-greatest
 intensity, it is correspondingly possible to weight the count, for example
 by counting the event N times if the intensity of a signal with a specific
 identifier at an antenna was highest, counting the event N-1 times if the
 intensity was second-strongest, counting N-2 times if the intensity was
 third-strongest, etc.
 The overall result is thus a reliable and quick allocation which, because
 it operates automatically, rules out possible operating errors. It is also
 possible to record transmitter modifications or even interchanges caused
 by possible wheel changes with no need for external action on the system.
 With this, at regular intervals the value of the list places or matrix
 cells for transmitters with allocated receiving antennas is set to a fixed
 value Ds, while the value of list places or matrix cells for transmitters
 without allocated receiving antennas is set to zero. The value Ds can be
 used to define a time after which the allocation is determined again. This
 could be done, for example, by counting down from the fixed value Ds at
 defined time intervals. Once the value of the relevant matrix cells or
 list places then reaches zero, the allocation is determined again. This
 could also happen each time the vehicle is started. Preferably an
 identifier is evaluated as belonging to the local vehicle only if the
 (optionally weighted) intensity of the received signal exceeds a threshold
 value. This increases the certainty that a wheel located in the vicinity
 but not belonging to the vehicle will incorrectly be recorded as belonging
 to the local vehicle. In addition, it is thereby possible to recognize
 malfunctions of the transmitter for a wheel belonging to the local
 vehicle, for example, the absence of a signal, excessively weak radiation
 of the signal, or the weakening or failure of a battery which is operating
 the wheel's transmitter. In this instance the central electronic receiving
 and analysis system can only record fewer than the reference number N of
 identifiers, and issue an error message. The system is also thereby
 prevented from recording, instead of the identifier of an onboard wheel,
 the identifier of a more-weakly received signal from a wheel which belongs
 to a different vehicle located in the vicinity.
 It often happens that signals are received from wheels which belong to
 other vehicles, i.e. from adjacent vehicles in parking lots, from vehicles
 passing by on the road, or, in a repair shop, signals from wheels which
 are stored in the vicinity of the vehicle; or even from wheels which are
 additionally being carried in the local vehicle on the occasion of a wheel
 change. Signals with identifiers which do not match stored identifiers
 allocated to the local vehicle are preferably not completely ignored, but
 rather are stored in the central electronic receiving and analysis system
 in a separate list or matrix, and pre-analyzed therein. Only if one or
 more identifiers have emerged as unequivocally dominant in the separate
 list or matrix, because they occur regularly or much more often than other
 identifiers, are they then included in the next recognition process
 executed according to the invention, in competition with the identifiers
 previously recognized and recorded as belonging to the local vehicle, so
 that any wheel changes performed in the interim can then also be detected
 and taken into account by the central electronic receiving and analysis
 system. It would also be possible, however, arbitrarily to initiate a
 recognition process according to the invention after each wheel change.