USOOS602524A
`
`1191
`United States Patent
`5,602,524
`[11] Patent Number:
`Feb. 11, 1997 [45] Date of Patent:
`Mock et a].
`
`
`
`[54] DEVICE FOR MONITORING THE
`AIR-PRESSURE IN PNEUMATIC TIRES
`FITTED ON VEHICLE WHEELS
`
`[76]
`
`Inventors; Markus Mock, Brunnwiesenstrasse 6,
`CPI-8610 Uster; Ernst Viillm. In Latten
`7, CH-8802 Kilchberg, both of
`Switzerland
`
`[21] Appl. No.:
`[22] PCT Filed:
`
`137,155
`Feb. 26, 1993
`
`[86] PCT No:
`
`PCT/EP93/00452
`
`§ 371 Date:
`
`Nov. 23, 1993
`
`§ 102(c) Date: Nov. 23, 1993
`
`[87] PCT Pub. No.: W093/16891
`
`3/1932 Pappasetal,
`.......................... 340/447
`4,319,220
` 9/1987 Vernon .........
`
`340/447
`4,695,823
`3/1988 Thomas et a1.
`..
`.. 340/447
`4,734,674
`
`11/1990 August Saint et al.
`.. 340/447
`4,970,491
`12/1990 Brown
`340/447
`4,978,941
`3/1991 Wang ..
`340/447
`5,001,457
`4/1992 Williams .
`340/447
`5,109,213
`6/1993 Brown eta].
`.. 340/445
`5,218,861
`
`.. 340/445
`7/1993 Sharpe et a1.
`5,228,337
`
`
`2/1994 Nowicki et a1.
`.. 340/447
`5,285,189
`FOREIGN PATENT DOCLMENTS
`
`
`
`3929316A1
`3930479A1
`
`3/1991 Germany.
`3/1991 Germany.
`
`Primary Examiner—Jeffery Hofsass
`Assistant ExaminerflDanicl J. Wu
`Attorney, Agent, or Firm—Parmelee, Bollinger & Bramblett;
`George W. Rauchfuss, Jr.
`
`PCT Pub. Date: Sep. 2, 1993
`
`[57]
`
`ABSTRACT
`
`Foreign Application Priority Data
`[30]
`Feb. 26, 1992
`[DE]
`Germany .......................... 42 05 911.9
`
`Int. Cl.5 ..................................................... B60C 23/02
`[51]
`[521 U.S. Cl.
`340/447; 340/825.54; 73/1465;
`ZOO/61.22
`340/447, 445,
`[58] Field of Search
`IMO/825.54; 73/1464, 146.5; ZOO/61.22
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`
`3/1975 Garcia
`3,873,965
`............. 340/447
`7/1979 Merz
`4,163,208
`. 340/447
`
`4,237,728 12/1980 Betts et a].
`340/447
`
`A device for monitoring the air pressure in pneumatic tires
`comprises a transmitting device fitted to each wheel of a
`vehicle and rotating with it, and a receiver which is built into
`the vehicle or accommodated in a separate housing. The
`transmitting device mounted in the wheel comprises a
`pressure gauge for measuring the tire pressure, a transmitter
`and a signal generator which generates an identification
`signal unique to each transmitter and transmitted before or
`after the pressure signal. The receiver processes received
`signals only when the identification signal received matches
`a reference identification signal stored in the receiver, This
`facilitates reliable operation of the monitoring device and
`prevents false alarms.
`
`21 Claims, 5 Drawing Sheets
`
`1
`
`I
`
`1
`29 \
`\Y/
`" _________
`1
`I
`SIGNAL
`;
`30'}
`I
`L-1 PROCESSING » —————————————————— 4
`
`I
`
`lI|I|III||L
`
`SIGNAL
`
`
`EMITTER
`MICRO—
`
`
`CONVERTING
`OUTPUT
`
` PRESSURE
`
`CIRCUIT
`
`PROCESSOR
`STAGE
`
`SENSOR
`
`
`23
`
`MEMORY
`
`
`
`26
`
`BATTERY
`
`
`Pet’r Exhibit 1001
`Continental v. Wasica
`IPR2014-00295
`
`Page 000001
`
`

`

`US. Patent
`
`Feb. 11, 1997
`
`Sheet 1 of 5
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`5,602,524
`
`
`
`FIG.1
`
`Page 000002
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`

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`US. Patent
`
`Feb. 11, 1997
`
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`US. Patent
`
`Feb.11, 1997
`
`Sheet 3 of 5
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`5,602,524
`
`PREAMBLE
`
`POST-AMBEL
`
`
`
`47
`
`[.5
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`FIG. 4
`
`Page 000004
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`US. Patent
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`Feb. 11, 1997
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`

`

`5,602,524
`
`1
`DEVICE FOR MONITORING THE
`AIR-PRESSURE IN PNEUMATIC TIRES
`FITTED ON VEHICLE WHEELS
`
`FIELD OF THE INVENTION
`
`The present invention concerns a device for monitoring
`the air-pressure in the air chamber of pneumatic tires of
`vehicle wheels.
`
`10
`
`Such monitoring devices are used, in particular, for the
`measurement of the air-pressure in the tires of motor vehicle
`wheels including lorries.
`
`BACKGROUND OF THE INVENTION
`
`The correct adjustment of the air-pressure of vehicle
`wheels is,
`to begin with, of an economical
`importance
`because an incorrect adjustment,
`that
`is, an air—pressure
`which is too high or too low, leads to an increased wear in
`the tire whereby the wheels of the vehicle must be replaced
`prematurely. This causes, in particular in the case of lorries
`whose tires are normally very expensive, unnecessary costs.
`A tire pressure which is too low also causes an increased
`consumption.
`However, of more importance than the economical aspect
`is the safety aspect. A faulty air-pressure in a vehicle wheel,
`in particular, air—pressure which is too low, causes an
`increased wearing—away of the rims of the tire, whereby the
`temperature of the tire is greatly increased and the strength
`of the tire rim is reduced. Due to this, the tire can suddenly
`be destroyed. Because the increased wear occurs, in par-
`ticular, when the speed is high, such tire damage often leads
`to severe traffic accidents.
`In order to avoid the economical disadvantages and, in
`particular, the danger of accidents, the air—pressure must be
`regularly checked, which by lorries means daily. However,
`the checking does not happen often because the tire pressure
`measurement is a relatively lengthy and also messy task
`which demands as well a certain technical skill.
`
`In the patent literature, different suggestions have there-
`fore been made to measure the tire air-pressure by way of
`pressure sensors arranged on the vehicle wheels, which
`measurement signal is then displayed in a suitable way to the
`driver. Such a suggestion is to be found, for example, in
`DE—3930479 Al.
`
`However, the realisation of such a monitoring device in
`practice hits against considerable difficulties.
`Since the vehicle wheel
`rotates during travel and a
`mechanical transmission of the measurement signals from
`the rotating wheel onto the non-rotating parts of the vehicle
`is normally not possible due to lack of space, the transmis—
`sion of the measurement signals must be carried out by way
`of a wireless transmission. Therefore, apart from infrared
`transmission and ultrasonic transmission, above all, electro—
`magnetic signal transmission is ofiered. However, the elec—
`tromagnetic signal transmission comes with problems since,
`in a vehicle a number of sources of electrical signals are
`already at hand, for example, the ignition system, the light
`mechanism, electrical operated blower, as well as other
`electrical assisted motors, etc. Apart from this, there are
`more than enough external sources of disturbance, for
`example, tramways, signal crossings, also radio senders and
`such like, which can influence the transmission.
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`Concerning the reliability of a monitoring device, high
`demands must be made. By a disturbance, if the monitoring
`device is then not in a position to reliably indicate the
`occurrence of a result by the monitor, then such a device
`cannot meet it’s contemplated purpose. However, on the
`other hand, should the monitoring device give off constant
`false alarms, then the driver will not consider the result any
`more and the system will then remain non-effective even
`when monitoring events have really occurred and are indi—
`cated.
`
`Furthermore, in view of the necessary reliability, it is also
`to be considered that because such a monitoring device is
`present, a manual test of the tire pressure does not take place
`any more because the drivers respectively go on the assump—
`tion that a false tire—pressure adjustment will be indicated by
`the monitoring device.
`The known monitoring devices in the art cannot fulfil
`these high requirements for reliability.
`Hence, the task of the present invention is to provide a
`monitoring device as described above, which will allow a
`reliable measurement and indication of the air—pressure, and
`respectively, the air—pressure change in the air—chamber of a
`pneumatic tire of a vehicle wheel.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the invention, this task is achieved by
`the device according to claim 1.
`Preferred embodiments of the invention are the objects of
`the dependent claims.
`In accordance with the device of the present invention, a
`pressure measuring device is provided which measures the
`prevailing pressure in the air-chamber of the wheel and
`outputs a representative electrical signal
`in accordance
`therewith. Depending on the construction and arrangement
`of the pressure measuring device, the measurement of the
`pressure can be carried out as the absolute pressure, that is,
`without reference to the surrounding atmospheric pressure;
`as an overpressure in reference to the atmospheric pressure;
`and as a difference pressure in reference to a predetermined
`reference pressure.
`The transmitting device is arranged on the vehicle wheel,
`the same as the pressure measuring device, and can be
`directly fixed to the valve, that is, to the inside of the tube
`or the tire, or can be fixed in a suitable way to the rim, for
`example, can be embedded.
`While the pressure measuring device and the transmitting
`device which can and must rotate with the wheel,
`the
`receiving device is formed together with the vehicle in a
`Stationary manner or is provided in a special transportable
`housing. Depending on the embodiment, each wheel of the
`vehicle can have it’s own receiving device attached to it, but
`it is also possible to provide a central receiving device; a
`receiving device which detects the respective signals from
`the wheels attached to an axis; and also receiving devices, in
`particular, for lorries, which collect the respective signals
`from a group of wheels, for example, a group of wheels
`arranged along a side of a lorry. The components of the
`receiving device can be such that they are spread out in
`different regions or combined together.
`The transmitting device comprises a control device pre-
`ferrably, a programme—controlled microprocessor which
`controls the emission of the transmitting signals. Further—
`more, the transmitting device comprises of a signal genera-
`tor device which gcncratcs a characteristic identification
`
`Page 000007
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`

`

`5,602,524
`
`IS
`
`20
`
`3
`signal for it’s respective transmission device. This signal is
`sent out at least once before or after the sending out of the
`pressure signal.
`The receiving device comprises a memory in which an
`identification—reference signal is stored, and which is related 5
`to the identification signal of the individual transmitting
`device. That is, the identification signal and the identifica—
`tion-reference signal are either identical or have a definite
`(mathematical) relationship to each other. A comparison
`device is provided in the receiving device which has the 10
`effect that a further processing of the pressure signal is only
`carried out if the identification signal,
`received by the
`receiving device after having been emitted from the trans—
`mission device, is identical with the identification-reference
`signal stored in the receiving device or has the predeter-
`.
`.
`.
`,
`mined relationship therewrth.
`By such an arrangement, an exceptional high reliability of
`the monitoring device and a great protection against distur-
`bances of the data transmitted between the transmitting
`device and the receiving device, is effected.
`It is improbable that a disturbance signal is created that
`corresponds exactly to the identification signal and can,
`therfore, be detected by the receiving device as a signal
`emitted from the individual transmitting devices. Therefore,
`these signals which have been coincidentally included into 25
`the emitted beam cannot lead to a false display or a false
`alarm of the monitoring device.
`Furthermore, with such an arrangement, the detection of
`an overlapping of the different signals emitted from the
`transmitting devices as measurement values which will, 30
`therefore, be falsely interpreted, is reliably prevented.
`In order to arrive at the optimal economical and operating
`safety of the vehicle, it is preferred that all the wheels of the
`vehicle are provided with a pressure measuring device and
`a transmitting device. In this case, there are various embodi-
`ments possible for the receiving device:
`I. The receiving device tan be laid out centrally and
`detects then the signals from all the wheels.
`2. For each wheel an almost independent receiver can be 40
`provided. However, in this case, it is preterrable that at
`least a common display device is provided in the
`dash—board or the like.
`
`35
`
`3. There could also be put together a mixed arrangement
`of the embodiment according to embodiments 1 and 2 45
`with which parts of the receiving device are de—cen—
`trally arranged in the area next to the wheels and other
`parts are combined in a central subeassembly. With
`such an arrangement, a receiver part can also be used
`for a number of wheels which, for example, can be 50
`arranged on an axis or on a side of the vehicle (for
`example, in the region of the double axis of a lorry).
`The receiver parts can be separated into any one of
`varying sub—assemblies or can be combined together. In
`extreme cases, the receiver parts arranged tie-central to 55
`the area next to the wheels contain only one antenna.
`In the case where all the wheels of a vehicle are equipped
`with a respective transmitting device, it is preferrable that
`the monitoring device, having a central or part-central
`receiving device construction, can provide a relationship 60
`between the received transmitted signal and the respective
`wheel position. This is also facilitated by the identification
`signal.
`This arrangement has clear advantages over the attempt to
`reduce the opposing disturbances from the individual trans— 65
`mitting devices on the wheels, that the transmitter only
`works with reduced intensity. A low transmittance intensity
`
`4
`has namely, the disadvantage that, the receiver must be
`formed with a correSponding sensitivity and, therefore, will
`be disturbed to a great extent by foreign signals. Further-
`more, with a battery operated transmitter it is difficult to
`keep the transmission intensity constant.
`The use of the identification signal also has the advantage
`when different kinds of vehicles are equipped with corre—
`sponding devices.
`Should a measurement be carried out in a stationary
`condition, that is, with the vehicle at a standstill, the distance
`to a neighbouring stationary vehicle can be very small, such
`that the receiver receives signals from both vehicles.
`Through the identification signal, it will be guaranteed
`that only the signals from the wheels belonging to the
`respective vehicle will be processed.
`Also in the condition when the vehicle is moving, for
`example, along a motorway having a number of lanes, the
`distance between the wheels of two vehicles can be so small
`that, for example, a difierence in the signal based on a
`weakening of the intensity, leads to false interpretation.
`In accordance with the invention, the monitoring device
`preferably comprises of a converting device which digitises
`the signals transmitted from the transmitter. With this
`embodiment, the reliability of the data transmission is fur-
`ther increased since insignificant changes in the signal do
`not influence the signals to be converted back in the receiver.
`The identification signal is then stored in the transmitter as
`a sequence of n bits whereby it is preferably 8, 16, 24, 32 or
`also greater. Due to a corresponding large choice of the value
`of 11, millions of different
`identification signals can be
`defined such that the danger that, for example, two trans-
`mitters accommodated in different vehicles have the same
`identification signal is exceptionally low and, for example,
`if the identification signal also contains a characteristic of
`the manufacturer, then such a danger is totally excluded.
`According to a preferred embodiment of the invention,
`the reliability of the monitoring device can be increased
`even more if the transmitter signal presented in digital form
`is coded to which additional bits are added which serve to
`recognise a false signal and to also correct a signal that is
`false. With this, the receiver can recognise a part of any
`possible false transmission and if need be can correct this.
`In the case where a transmitter is always related to a
`particular receiver, which is not always possible, the emitter
`and the receiver can have the respective identification signal
`and the identification reference signal stored already by the
`manufacturer. It is, however, preferred that either the iden-
`tification signal of the transmitter or the identification signal
`of the receiver is changeable. This version is normally
`preferred since this will allow the costs of mounting the
`transmitter to the wheel to be reduced.
`In both cases, appropriate devices are provided so that the
`respective changeable identification signal
`cannot be
`changed by chance.
`The signal
`transmission from the transmitter to the
`receiver can be carried out continually or non—continually.
`With the continual transmission, the pressure is measured
`within predetermined intervals of, for example, one minute,
`and a corresponding signal
`is sent out. This method is
`particularly suited for when it is to be used in continual
`monitoring operation, that is, if the air-pressure is to be
`monitored during the whole journey. Attempts have shown
`that with this operating mode, the capacity of a small lithium
`battery is sufiicicnt which delivers the energy for the trans-
`mitter for around five years.
`For the non-continuous operation, there are given basi—
`cally two possibilities:
`
`Page 000008
`
`

`

`5,602,524
`
`5
`With the first alternative, the tire pressure is continually
`monitored by a mechanical device. This can be carried out,
`for example, by a membrane which closes a reference
`chamber in comparison with the tire pressure as is described
`in EP—A—04l7712 or in EP—A—04l7704. As soon as the
`pressure of the tire changes by a particular amount with
`respect
`to the reference value, a switching member is
`activated by way of the membrane and causes transmission
`of the pressure signal and it’s identification signal. This
`device has the advantage that it requires only a relatively
`small amount of electrical energy and can, therefore, be
`operated with a small battery. However, the disadvantage is
`that a malfunction of the transmitter by way of the receiver
`is possibly not recognised.
`With the second alternative of non—continuous operation
`which, of all things, is suitable for the one—off measurement
`of the air-pressure before travel begins or during a travel
`stop, the pressure measurement and the transmission of the
`transmitter signal is initiated externally. Since the start signal
`should be transmitted with no contact as well, the transmitter
`must be arranged with an additional second receiver which
`at the same time rotates with the vehicle wheel and which
`receives the start signal for the pressure measurement, and
`so that by way of the control device the pressure measure-
`ment can be activated.
`Furthermore, it is possible, in particular, with a transmitter
`mounted on a valve to provide a switching device in order
`to manually start the measurement.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Further advantages, features and embodiments of the
`present invention will now be described in reference to the
`enclosed drawings.
`In the drawings are shown:
`FIG. 1. A first example of an embodiment of the moni-
`toring device of the present invention employed in a vehicle
`having four wheels;
`FIG. 2. A schematic block diagram of the construction of
`the transmitting apparatus used in the embodiment accord-
`ing to FIG. 1;
`FIG. 3. A schematic representation of the signals emitted
`from the transmitting device according to FIG. 2;
`FIG. 4. A schematic representation of the modulation of a
`transmitted signal;
`FIG. 5. A schematic block diagram of the construction of
`the receiving device of the embodiment according to FIG. 1;
`FIG. 6. A schematic block diagram of the receiving device
`according to a further embodiment of the invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`A first embodiment of the invention will now be described
`in reference to FIGS. 1 to 5 of the drawings. This embodi—
`ment represents a motor vehicle comprising of four wheels
`each having an respective metal rim with a tire arranged
`thereon. Between the tire and the mm, a circumferential
`hollow space is formed which, in a so—called tubeless tire, is
`air—tight and therefore forms the air chamber of the wheel. In
`tires having a tube, an air—tight tube is inserted into this
`hollow space. The feeding of air into the air chamber is
`carried out via a valve, which in tubeless tires is directly
`provided on the rim and in tires having a tube, a bore is
`provided in the rim through which the valve is placed.
`
`10
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`15
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`20
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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
`
`60
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`65
`
`6
`On every wheel R1 to R4 a transmitting device 81 to S4
`is fixed which rotates with the respective wheel.
`Further, four receiver parts E1 to E4 are provided which
`are fixed on the vehicle body; on the wheel suspension or the
`like, and which are connected via an electrical connection to
`a central control device 2, which on one side is connected
`with a display device A.
`As will be made more clear in the following description
`in reference to FIG. 2, the transmitter devices 51 to S4
`contain a pressure-gauge, a transmitter, a transmitter-con-
`troller, a memory device, etc.
`In every transmitter device, a pressure sensor (18) is
`provided which is connected with a signal converting circuit
`(20) via an electrical connection which is represented here
`and in the following only schematically.
`Whenever the absolute pressure is to be measured, which
`for this embodiment is the case, a piezoelectric—type sensor
`is preferably used as the pressure sensor which can work
`with a battery voltage of under 5 volts. Deviating from this
`arrangement, instead of measuring the absolute pressure, a
`pressure difference with respect to a reference pressure can
`also be measured and processed, which arrangement is
`known in the art. Further, it is also possible to arrange the
`pressure gauge to measure the pressure only when the
`pressure falls below a predetermined absolute or relative
`value.
`
`Should the pressure sensor (18) directly measure the
`pressure difference with respect to the atmospheric pressure,
`then a connection must be made between the pressure gauge
`and the surroundings.
`In accordance with this embodiment, the analogue signal
`of the pressure sensor is converted in the signal convertion
`circuit (20) to a digital signal by way of a AID converter. The
`signal converting circuit (20) is further connected to a quartz
`controlled interval-timer (21) whose purpose is still to be
`explained. The digitally-converted signal is transferred to a
`microprocessor-computer (22) which is connected with a
`memory (23) which receives, as well, the signals from the
`interval-timer (21).
`In the memory (23), which is separated into any single
`and, as well, varying memory areas, a programme is stored
`which controls the microprocessor, the programme being
`stored either in a continual memory or in a memory whose
`contents are guaranteed over a long term by the battery
`voltage. Furthermore, the identification signal of the trans-
`mitter is also stored in digital form in this memory (23). By
`means of the microprocessor the signals to be transmitted
`are converted into an emitter signal and led to an emitter
`output stage (25). This signal is transmitted from the emitter
`output stage (25) to an antenna (26). A battery (28) which
`rotates with the wheel, which preferably is a lithium battery,
`is provided to supply current to the emitter device.
`The functioning of the transmitting device is as follows:
`The transmitting device is normally to be found in the
`stand—by mode, in which mode only the interval-timer (21)
`is working in order to save on the capacity of the battery.
`After preset time intervals, for example, every 60 seconds,
`the interval-timer gives out a signal which changes the
`microprocessor (22) from the stand-by mode to the active
`mode. After activation of the microprocessor, a pressure
`measurement is made which is controlled by the programme
`in the memory (23). Finally, an emitter signal is transmitted
`whose composition is schematically represented in FIG. 3.
`The signal
`sequence comprises of a preamble of,
`for
`example, 16 bits, which enables the receiver to have syn—
`chronisation with the emitter signal. Then follows on the
`
`Page 000009
`
`

`

`5,602,524
`
`7
`identification signal which contains an identification char—
`acteristic specific to the transmitter. The identification signal
`is, in this embodiment a binary number having 32 or more
`bits, which is stored in the memory (23) of the transmitter
`device. To the identification signal follows on a data block
`which, for example, comprises of 24 bits and contains the
`measured pressure value in binary form. From this follows
`a post—arable of, for example, 4 bits which completes the
`signal.
`To increase the transmission safety, the signal is changed
`by the inclusion of check bits which allow recognition of
`false signals received in the receiver and correction of these
`false signals.
`-he emitter device can be so controlled that this signal
`sequence is sent out only once. To increase the safety, a
`fea urc which is particularly addressed by the present inven-
`tion, it is, however, preferable that the signal is transmitted
`a p urality of times one after the other. As will be described
`later, it is possible with this superfluous transmission,
`to
`check in the receiver device, if a number of identical signals
`have been received. If this is not the case,
`then further
`processing will not take place. Due to this measure, the
`protection against disturbances can be suitably improved.
`The signal transmission from the transmitter device to the
`receiver is carried out by way of an electromagnetic radio
`wave of constant frequency. A quartz controlled interva1~
`timer (2]) serves to control
`the transmitter frequency. In
`consideration of the quality of transmission, it is preferred to
`use a frequency from around 8,000 hertz or around 4,000
`hertz.
`
`
`
`This carrier signal must be modulated in a suitable way in
`order to transmit to the receiver device the digital informa-
`tion which is present.
`there are considered the
`As methods of modulation,
`amplitude shift keying method (ASK), the frequency shift
`keying method (FSK) and phase shift keying method (PSK).
`It has already been suggested to use the frequency shift
`keying method for transmitting the tire air pressure whereby
`the contents of the hit information 0 and 1 correspond to
`varying frequencies. With this method, however, two fre-
`quencies must be transmitted which increases the cost on the
`side of the transmitter and receiver.
`
`Attempts have shown,not only from the cost but also from
`the quality of transmission, that it is particularly favourable
`to use the Phase Shift Keying (PSK) modulation method,
`and, in fact, in a special variant, the Difierential Phase shift
`Keying (DPSK) is preferred.
`With this method, the emitter signal experiences a phase
`jump whenever a 1 is conveyed; should a 0 be sent, the
`emitter signal remains unchanged. The phase jump is 180°.
`An example of this modulation is shown in FIG. 4.
`Here, in the upper part of the diagram above the time axis
`(40), a bit sample is shown by way of an ordinate (41)
`comprising of bits 0, 1, 1, 0, 1, 0, 0, 0, 1, 1, .
`.
`.
`In the diagram, shown directly under, above the same
`scaled time axis (45) and the voltage axis (46), a voltage
`signal (47) is represented which comprises a frequency
`which stays constant, which signal is characterised in the
`change of phase by the above-mentioned DPSK—modulation
`of the bits sample.
`The construction of the receiver device will now be
`described in reference to FIG. 5.
`In this embodiment, the receiver device divides itself into
`a first receiver part E1 to E4, which is respectively arranged
`close to the wheels R1 to R4 and in a second central
`receiving part (EZ).
`
`10
`
`15
`
`20
`
`25
`
`30
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`Every first receiver part E1 to E4 comprises of an antenna
`(60) whose signal is conveyed to a signal-processing and
`amplifying circuit (61) in which the signal is amplified and
`filtered. Then the signal is demodulated in a demodulator-
`stage (62) and is then available as a digital signal which
`corresponds to the modulated digital signal in the respective
`transmitting device. This signal sequence also includes the
`added check bits to recognise a false signal, which are
`checked in the decoder device (63) and taken out.
`The decoding device is operated as a logic circuit and
`comprises a memory with changeable contents in which the
`identification-reference signal as well as a pairing—mode
`recognition signal is stored. In the decoding device (63) a
`comparison circuit is also included which compares the
`received, converted back signal with the stored identifica-
`tion-reference signal and the pairing—mode recognition sig—
`nal. The signal processing circuit (61), the demodulating
`state (62) and the decoding device (63) are preferably
`combined as a special purpose integrated chip, that is a so
`called ASIC. This construction has the advantage that the
`signal processing and the comparison with the stored signal
`is carried out very quickly and does not burden the micro—
`processor of the central receiving device.
`The demodulated and decoded digital signals are then
`conveyed to a central receiver part (EZ) which is connected
`via an electrical connection to the first receiving components
`E1 to E4. There the digital signals are conveyed by a
`microprocessor (66) which is controlled by a programme
`contained in the memory (68) and which also receives the
`data. The time control of the receiver device is carried out by
`an interval—timer (69).
`The microprocessor is further connected with a signal
`processing device (71) which produces signals, which are
`displayed in the device formed as a display (73). The actual
`surrounding pressure is measured with a pressure sensor
`(72) and is conveyed through a signal processing stage (67)
`of the microprocessor (66) in case it should happen that the
`tire air—pressure is indicated as being overpressure, that is, as
`a different pressure to the atmospheric pressure.
`The functioning of the receiver device now follows:
`The emitted signal from the respective transmitting device
`is received b the antenna (60) and is digitally converted in
`the chip which follows, and is then conveyed to the micro-
`processor of the decoding device. After reciept of a signal,
`the comparison circuit checks if the identification signal
`matches the stored identification signal. If this is the case,
`the corresponding data value is evaluated and transmitted to
`the central receiving component (EZ). As explained above,
`the emitted signal is repeated a number of times in order to
`avoid false transmissions and is checked if the successive
`signals have the same sequence. No storage of the signals is
`carried out if deviations are determined between the suc-
`cessive signals.
`From the above, it can be taken that the identification
`signal and the identification-reference signal are identical.
`The checking of the identity can be carried out such that the
`microprocessor subtracts one of the digital numbers from the
`other and determines that it is identical if the result is 0.
`However, it is also possible that the identification—reference
`signal is not in fact identical with the other signal, but are
`related to each other in a mathematically defined way. The
`identification-reference signal can be formed, for example,
`as a complimentary value to the comparison signal, that is,
`that the addition of both numbers leads to the result 0. But
`also other mathematical arrangements are possible, for
`example, a set difference between the two numbers.
`
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`5,602,524
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`9
`In order to avoid a theoretical possible collision of the
`signals emitted from the dilTerent transmitting devices inde—
`pendent of each other, these signals are preferably controlled
`by means of a random circuit so that the emittance does not
`take place directly after the measurement of the pressure
`signal, but rather with a random delay within a predeter—
`mined time region, that is, for example, within 26 seconds
`after the measurement of the pressure signal. As such, it can
`be avoided that two transmitting devices which send out
`signals within the same time interval will over a long time
`collide with each other. In case a col