The present invention relates to vehicle tyre monitoring devices.

It is now relatively commonplace to provide road vehicles with a plurality of electronic sensing devices to monitor the performance of individual components and then output signals indicative thereof to a vehicle controller. A particular example is provided by tyre pressure monitoring systems (TPMS), which typically comprise a tyre monitoring device incorporating a pressure sensor and an RP transmitter disposed within the tyre. These devices may typically have an integral power source such as a Lithium battery. These batteries typically have a limited life time and have a limited temperature range of reliable operation. Alternate power sources such as energy converters and/or energy scavenging means such as magnet/coil combinations, thermo-electric means, RF power extraction circuitry or piezo-electric means have been heavily investigated for the provision of an improved solution.

In one known tyre monitoring device, disclosed in US2003/0209063, power is provided by piezo-electric material. In this case, a patch containing piezo-electric fibres is mounted on the interior of the tyre. The tyre and thus the patch flexes and vibrates when the vehicle is in motion. This causes current to flow in the piezoelectric fibres, which can be harnessed to power the Tyre monitoring device.

In order for such a TPMS to operate usefully, the vehicle controller must be able to identify each Tyre monitoring device and also identify which Tyre monitoring device is associated with which tyre. Typically, each Tyre monitoring device is

provided with a unique identification code which is incorporated into every

transmission to the vehicle controller. The vehicle controller is provided with a data storage means operable to store identification codes of each Tyre monitoring device so that transmissions can be identified, hi order for the vehicle controller to associate the identification codes of each TPM device with a particular tyre, manual intervention of some form is normally required. This is of course costly and

inconvenient.

One proposed method of overcoming this problem is disclosed in US6633229 and US6446502 wherein the tyre monitoring devices in each wheel additionally incorporate accelerometer means. When each tyre monitoring device transmits signals to the vehicle controller, it also transmits data from the accelerometer means. By processing the acceleration data, each tyre monitoring device may be associated with a particular wheel: for distinguishing between spare wheels and those currently in use, the centrifugal acceleration of each wheel is considered (spare wheels having no centrifugal acceleration as they are not turning); for distinguishing between wheels on the left and the right of the vehicle the sign of any acceleration along the circumference of the tyre is considered, such acceleration having a different sign for tyres on different sides of the vehicle as long as each device is aligned in the same manner in each tyre; for distinguishing between steering and non-steering wheels either an integral of the centrifugal acceleration is considered or the acceleration perpendicular to the circumferential and centrifugal accelerations is considered. This however relies upon the tyre monitoring devices in each wheel being correctly

orientated and having accelerometer means which can measure acceleration along

either two or three different axes. The provision of such accelerometers increases the

cost of such tyre monitoring devices and also puts an additional calculation burden on the vehicle controller. Furthermore these methods assume the presence of batteries as

integral power source.

It is therefore an object of the present invention to provide a new tyre monitoring device and in particular a new tyre monitoring device which facilitates automatic association of the tyre monitoring device with a particular tyre.

According to a first aspect of the present invention there is provided a tyre monitoring device comprising: a pulse generator for generating a pulse signal in response to deformation of the tyre; and data transmission means operable to transmit a signal in response to said pulse.

The rotation rate of the tyre, when in motion can be determined from the time interval between transmitted signals. By considering the rotation rate of the tyre, it is possible to determine which tyre of a vehicle the device is fitted to. Additionally the size of the deformed patch of the tyre, when in motion, can be determined from the time interval between transmitted signals. Thus whether or not the tyre is in a safe condition for the current load can be determined without the use of any additional sensing means in the monitoring device. This thus provides a relatively inexpensive device for monitoring the condition of a tyre.

The device may be provided with an energy scavenging means. The energy

scavenging means is preferably an energy converter operable to scavenge energy to power the device. The energy scavenging means may comprise any suitable energy scavenging energy converter including, but not limited to, any one of magnet/coil

combinations, thermo-electric means, RP power extraction circuitry and piezo-electric

means.

In a first embodiment the pulse generator comprises analysing means connected to energy scavenging means, operable to output a pulse in response to variations in a signal output by the energy scavenging means. The pulse generator is preferably mounted on the inner surface of a tyre to be monitored, and thus the signal output by the pulse generator will vary in response to deformation of the tyre as it rotates. The analysing means is preferably operable to generate a pulse in response to: increase or decrease of the signal output by the energy scavenging means above or below a predetermined value; an increase or decrease of the signal output by the energy scavenging means by greater than a predetermined value; or by increase or decrease of the signal output by the energy scavenging means by greater than a predetermined rate. In an alternative embodiment, a plurality of pulse generators may be provided or a plurality of energy scavenging means may be connected to a single pulse generator.

The analysing means may be integrated into or mounted upon the energy scavenging means. Alternatively, the analysing means may be provided separately from the energy scavenging means, m particular all components of the device other than the energy scavenging means may be provided on a single integrated circuit (or a plurality of interconnected integrated circuits) packaged in a protective housing.

The energy scavenging means is preferably a piezo-electric patch comprising piezo-electric fibres unidirectionally aligned in a resin matrix. Such a patch outputs

an electric current when subject to vibration or deformation, the magnitude of the current determined by the amount of vibration or deformation.

In some preferred embodiments, the piezo-electric patch may be the energy scavenging energy converter as well as a component of the pulse generator. Alternatively, one or more additional piezo-electric patches may be provided to be the

energy generating means.

Preferably, an energy storage means is provided. This may be a storage means where excess energy generated by the energy scavenging means and or the pulse generator is stored. The energy storage means may be a capacitor or an electrochemical storage means such as a rechargeable battery.

An energy management unit may be provided, operable to allocate energy from the energy storage means and the energy scavenging means to the various components of the device.

The pulse generator may be affixed to the tyre to be monitored. The pulses are generated when the pulse generator is in the region of the tyre that is deforming or flexing to contact the road surface or when the pulse generator is in the region of the tyre that is rebounding from deforming to contact the road. In embodiments wherein the pulse generator is adapted to generate a single pulse per revolution, the pulses generated correspond to the edges of said energy scavenging means either entering or leaving said region of the tyre in contact with the road surface. The pulses may be used to calculate the revolution rate of the tyre.

In embodiments wherein the pulse generator is adapted to generate two pulses per revolution, the pulses generated correspond to the edges of said energy scavenging means entering and leaving said region of the tyre in contact with the road surface. The pulses may - additionally to the single pulse embodiment - be used to measure the size of the deformed part of the tyre.

These calculations may be carried out by processing means provided in the monitoring device or by external processing means, as desired. The calculation may be used to determine which tyre monitoring device on a vehicle is mounted on each

wheel.

The data transmission means may be operable to transmit a signal after each pulse generated by the pulse generator or may alternatively be operable to transmit a signal after either a predetermined number of pulses or a predetermined time interval. If signals are not transmitted after every pulse, said signal may include information on the number of pulses that have been generated since the last pulse and the time intervals or average time intervals between said pulses.

The tyre monitoring device may incorporate an identification code. This code is preferably included in each signal transmitted by the data transmission means.

The device may additionally comprise sensing means, said sensing means operable to sense a condition of the tyre. In some embodiments a plurality of sensing

means may be provide to sense different conditions of the tyre. Tyre conditions that may be sensed include, but are not limited to: pressure; acceleration; temperature; speed; and vibration.

The data transmission means preferably is operable to transmit signals at RF frequencies. The data transmission means may comprise an encoder, a resonator and an antenna. In embodiments wherein sensing means are provided, the encoder is operable to: receive signals from the sensing means; receive RF signals from the resonator; combine said signals to provide an RF output signal; and pass said RF output signal to the antenna for transmittal to remote circuitry. The resonator may be an SAW (Surface Acoustic Wave) resonator or may be a crystal driving a PLL (Phase Lock Loop).

In embodiments wherein sensing means are provided, the data transmission means are preferably operable to transmit a signal indicative of the output of the sensing means to external circuitry in response to the pulse signal. If the data transmission means is not operable to transmit the output of the sensing means after every pulse generated, it may be operable to transmit information relating to the average output of the sensing means since the last transmission and/or information relating to the extremes of the output of the sensing means since the last transmission and/or information relating to the output of the sensing means at the time of generation of some or all of the intervening pulses.

According to a second aspect of the present invention there is provided a tyre monitoring device comprising: a pulse generator for generating a pulse signal in response to deformation of the tyre; sensing means for sensing tyre conditions and

generating a signal indicative thereof; and data transmission means operable to

transmit a signal indicative of the output of the sensing means to external circuitry in response to the pulse signal.

The rotation rate of the tyre, when in motion can be determined from the time interval between transmitted signals. By considering the rotation rate of the tyre, it is possible to determine which tyre of a vehicle the device is fitted to. Additionally, the size of the deformed patch of the tyre, when in motion, can be determined from the time interval between transmitted signals. Thus combining the tire deformation information with the vehicle load sensors, the external circuitry can determine whether or not the tyre is in a safe condition for the current load. This thus provides a relatively inexpensive device for monitoring the condition of a tyre and the vehicle stability.

The monitoring device according to the second aspect of the present invention may incorporate any or all features as described in relation to the first aspect of the present invention as desired or as appropriate.

According to a third aspect of the present invention there is provided a method of monitoring a tyre when the tyre is in motion using a tyre monitoring device according to the first or second aspects of the present invention, said tyre monitoring device being fitted to the tyre, comprising the steps of: detecting signals transmitted by the device; determining the time interval between said signals; and thereby determining the proportion of the tyre surface that is in contact with the road surface.

The method may incorporate the further step of determining whether the proportion of the tyre surface in contact with the road indicates that the tyre is in a

safe condition. This may be achieved by comparing the determined proportion with values from a look up table or with values calculated by a suitable algorithm. The

look up table or algorithm may also utilise or require additional input from the vehicle load sensors, such as ride height sensors. Using this method, it is possible that a larger operational range, in terms of weather conditions, road condition, tire inflation or tire wear, for tire use can be envisaged, as this test directly measures tyre road contact rather than estimating tyre road contact based on a variety of indirect parameters. Furthermore, use in conjunction with such systems as active suspension can compensate partially for changes in tire performance within the applicable range.

Since the tire location is known, different algorithms/look up tables may be provided for front and rear tyres, if desired. If a tyre is determined to be in an unsafe condition the method may include the further step of issuing an alarm.

According to a fourth aspect of the present invention there is provided a method of monitoring a tyre when the tyre is in motion using a tyre monitoring device according to the first or second aspects of the present invention, said tyre monitoring device being fitted to the tyre, comprising the steps of: detecting signals transmitted by the device; determining the time interval between said signals; and thereby determining the rotation rate of the tyre.

The method may incorporate the further step of comparing the determined rotation rates of each tyre to information obtained from other vehicle sensors to determine which tyre is linked to which wheel of the vehicle. The additional sensors may be wheel or axle rotation rate sensors and may comprise part of a vehicle anti- lock braking system. In order for the determination to take place, it may be necessary for the vehicle to complete one or more changes in direction, so that differential wheel rotation rates may be observed and matched.

The vehicle sensors may alternatively comprise sensors of the type used vehicle stability sensors, for instance steering wheel angle sensors, gyroscope, low G acceleration sensors or similar.

According to a fifth aspect of the present invention there is provided a method of determining the particular tyre on a vehicle to which a tyre monitoring device is fitted comprising the steps of: fitting a tyre monitoring device according to the first or second aspects of the present invention to each tyre; providing vehicle sensors for determining information relating to one or more aspects of vehicle performance; analysing the output of the tyre monitoring device to determine the revolution rate of each tyre; analysing the output of the vehicle sensors; and comparing the output of each tyre monitoring device to determine which tyre is linked to which wheel of the vehicle.

According to a sixth aspect of the present invention there is provided a tyre monitoring system for a vehicle comprising: a tyre monitoring device according to the first or second aspects of the present invention fitted to each tyre of the vehicle; vehicle sensors for determining information relating to one or more aspects of vehicle performance; and processing means operable to receive signals from each tyre monitoring device and from the vehicle sensors and to thereby determine which tyre is linked to which wheel of the vehicle.

The system of the sixth aspect of the present invention can be used in conjunction with any or all of the methods of the third, fourth and fifth aspects of the

present invention. Similarly, the system of the sixth aspect of the present invention

may incorporate any of the features described hereinabove in relation to any of the previous aspects of the present invention as required or as desired.

The system may be used as part of a stability control system for a vehicle. It can also allow diagnostic tests to be carried out, for instance to determine whether one side of a vehicle is overloaded.

The system may also incorporate means for outputting information relating to the condition of the tyres. The system may further incorporate means for outputting an alarm if any tyre is in an unsafe condition.

In embodiments wherein the devices incorporate sensing means, the condition of the tyres may be determined, at least partially, based on the output of said sensing means.

In order that the invention is more clearly understood, it will now be described further herein, by way of example only, and with reference to the following drawings, in which:

Figure 1 is a schematic block diagram of a first embodiment of a tyre monitoring device according to the present invention; and

Figure 2 is a schematic block diagram of an alternative embodiment of a tyre monitoring device according to the present invention;

Figure 3 is a schematic block diagram of a second alternative embodiment of a tyre monitoring device according to the present invention; and

Figure 4 is a schematic block diagram of a third alternative embodiment of a tyre monitoring device according to the present invention.

Referring now to figure 1, a tyre monitoring device 100 comprises sensing means 101, a pulse generator 102, an energy scavenging means 103, an energy management unit 104, an energy storage means 106 and data transmission means, the data transmission means comprising an encoder 107, a resonator 108 and an antenna 109.

The pulse generator 102 is operable to generate a pulse when the tyre flexes, this pulse is detected by the sensor 101. The sensing means is operable to sense a condition of the tyre and upon detection of a pulse from the pulse generator 102 to output a signal indicative of the tyre condition to the encoder 107. The encoder 107 combines the signal from the sensing means with an RF reference signal generated by the resonator 108 and outputs the resultant signal to the antenna 109, thereby transmitting an RF signal indicative of the tyre condition to external circuitry. In addition to transmitting tyre condition information, the data transmitting means transmits a identification code, identifying the device 100 making the transmission.

The energy management unit 104 is operable to allocate to the sensing means

101 and the data transmission means sufficient energy for operation from either the energy scavenging means 103 or the energy storage means 106. The energy

management unit 104 is also operable to divert energy from the energy generating means 103 to the energy storage means 106 where possible.

In figure 2, an alternative embodiment is shown wherein the pulse generator 102 and the energy scavenging energy converter 103 are provided by a single energy generating means 105. In all other respects this embodiment is the same as that of figure 1.

The pulse generator 102/105 comprises a piezo-electric patch which, in use is affixed to the interior surface of a tyre and an analysing means, the analysing means is operable to output pulses in response to variations in the signal output by the piezo- electric patch. The patch is flexible and may be affixed to the surface of the tyre by means of an adhesive or any other suitable means. The patch is typically a patch of the type comprising piezo-electric fibres unidirectionally aligned in a resin matrix. As the wheel to which the tyre is fitted turns, the portion of the tyre in contact with the road surface flexes and deforms. This causes the piezo-electric patch to deform generating an electric current.

If the piezo-electric patch is small relative to the deformed region of tyre in contact with the road surface, a substantial current only flows when the patch is in the region of the tyre that is deformed. The analysing means is operable to detect the rising or falling edge of the signal generated when the patch is in the region of the tyre that is deforming to meet the road surface or in the region when the tyre is rebounding back to normal after losing contact with the road, thus providing two pulses per revolution. Alternatively, it is possible to provide a plurality of patches connected to

said analysing means and thereby generate additional pulses or generate pulses in response to different analysis of the signals from the patches. If the patch or patches forming the pulse generating means are separate to the patch or patches forming the energy scavenging means 103, an energy scavenging patch may be provided between two pulse generating patches.

By determining the time interval between pulses, the proportion of the tyre surface in contact with the road can be determined and additionally, the revolution rate of the tyre can be determined. This can provide a good indication of how safe the tyre is without directly sensing the tyre temperature, pressure etc.

If the revolution rate of a tyre is known, this allows a vehicle controller to determine which wheel each device is provided on without manual intervention. This is achieved by comparing the revolution rate of each tyre with the revolution rate of each axle to which the tyre is connected (via a wheel). The tyre and axle with a matching revolution rate are connected. The axle revolution rate can be determined by axle rotation rate sensors and this may conveniently be measures by sensors forming part of an anti-lock braking system.

In order that each separate device 100 may be identified, each device has an identification code that is included in all transmissions.

It may take a few moments to determine which tyre is connected to which axle as the rotation rates will normally only vary between tyres when the vehicle is turning. Once each device is associated with a tyre, the vehicle controller stores the identification codes of each tyre and is thus able to monitor the condition of each tyre

individually. This procedure can be carried out each time the vehicle is switched on.

An advantage of this is that a driver may now fit new tyres to the vehicle and have those tyres monitored by the vehicle controller without having to update the information stored in the vehicle controller. This also means vehicles can be supplied with means for receiving signals from such tyre monitoring devices hard wired and allow drivers to choose whether to implement the system by buying tyres fitted with monitoring devices or by fitting such monitoring devices themselves. It also enables a faulty monitoring device to be replaced with another monitoring device without updating the vehicle controller.

In order to reduce the number of transmissions, rather than after every pulse transmissions can occur after predetermined time intervals or after predetermined numbers of pulses. In such cases transmissions may include data on the number of pulses and/or the average intervals between pulses in the interval since the last transmission.

The revolution rate of each tyre may be combined with other tyre conditions sensed by the sensing means to calculate a tyre wear value e.g. by integrating any or all of rotation rate, pressure and temperature. Information relating to any or all of these parameters may be displayed to a user of the vehicle. Alternatively, information relating to whether the tyre is in a safe condition, determined by reference to the output of the monitoring device may be displayed. If a tyre condition becomes unsafe, an alarm may be output.

In an alternative embodiment, shown in figures 3 and 4, a simpler version of the monitoring device 100 is shown which omits the sensing means 101, but in other respects is similar to the embodiments of figures 1 and 2. Such a device may be used for determination of the proportion of the circumference of the tyre in contact with the road at any one time and for determination of the rotation rate of the tyres. It can therefore be identified as being fitted to a particular tyre by the vehicle controller and also provide an indication of whether a tyre is safe. As such this embodiment can provide a useful indication as to the condition of a tyre and by omitting one or more sensors provides such an indication at a lower cost.

In each of the above embodiments, the various components of the device other than the patch may be provided on a single integrated circuit or may be provided on a plurality of interconnected integrated circuits. Such integrated circuits may be packaged individually in separate protective housings or may be packaged in a single shared protective housing.

Referring now to figure 5, there is shown a schematic diagram of a tyre 200 deforming on contact with a road surface and the relative timings of events in the monitoring device 100 triggered by the deformation of the tyre 200. hi figure 5a, the tyre 200 is rotating in a direction 202 and the deformed portion 204 (contact patch) currently in contact with the road surface is deformed so as to be flat whereas the rest of the tyre 206 is its normal curved form. As the tyre rotates, any monitoring device 100 fitted to the tyre will pass through the deformed portion 204 and normal portion 206 of the tyre over time.

The timing diagrams of figures 5b to 5f illustrate the operation of a preferred embodiment of the invention which uses RF transmissions with a short duration relative to the relative to the time the monitoring device spends in the deformed region 204 of the tyre on each revolution. The RF transmissions are transmitted using a dataframe. An external receiver decodes this information and feeds it to the vehicle controller, which latter compares the timing information from the transmissions with the timing information from other vehicle sensors.

Turning now to figure 5b, the output 210 of the piezo-electric patch is shown. At time tO a first deflection occurs marking the start of the contact patch 204, at time tl a second deflection point marking the end of the contact patch 204 occurs. This sequence is repeated at times t2 and t3. Time interval A between tO and tl provides an indication of the extent of the contact patch, and thus provides information about the total tire deflection. In particular the ratio of time interval A to time interval B (between tl and t2) provides an indication of the size of the contact patch 204 in proportion to the surface of the tyre 200. Comparing this with the vehicle load from other vehicle sensors, allows an assessment of the safety of the present driving condition to be carried out. This assessment may be used to vary the operation of other variable parameters, such as active suspension, to improve vehicle performance.

The sum of time intervals A and B is the time period of a single tyre revolution. As described above, by comparing the rotation period or the rotation rate determined by each tyre monitoring device with the same quantity determined by the

ABS sensors for each wheel or axle, the wheel each tyre is mounted on can be determined. The output of each tyre monitoring device can additionally or

alternatively be analysed in the light of information from a steering angle sensor to determine which tyre is associated with which wheel of the vehicle.

Turning to figure 5c, it can be seen that the encoder 107 is operated throughout time interval A. Figures 5d and 5e show respectively the times 220, 230 at which data is transmitted by the tyre monitoring device 100 and received by external receivers. Figure 5f illustrates that in embodiments wherein sensors are provided, the sensors remain active throughout the revolution but their outputs are only encoded during time interval A and only transmitted at the times shown in figure 5d.

Turning now to figure 6a, the structure of a transmitted dataframe 300 is shown schematically. The dataframe 300 starts with a preamble 301 to allow a receiver to lock on to the signal. A synchronisation sequence 302 is then transmitted to allow the receiver to set is time stamp as a reference point to compare between different transmissions. Then a configuration sequence 303 is transmitted which allows the receiver to understand the content of the transmitted dataframe. Next an identification code 304 is transmitted to allow the receiver to identify the transmitting monitoring device 100. The variable data 305 is transmitted next. This can contain physical sensor data like pressure, temperature, measured forces inside the tire, etc., and/or timing information like the particular slot that has been used to transmit the data, and/or the amount of revolutions that have occurred since the last transmission. Finally a verification sequence 306 (CRC, checksum, parity, ...) is transmitted to provide the receiver of an indication as to whether the reception was well received or not. Both the configuration sequence 303 and the verification sequence are optional

and can be omitted if desired. Also shown is figure 6b, indicating a dataframe 311 used by an external device for transmissions to said monitoring devices in embodiments wherein the monitoring device is adapted to receive signals. As above dataframe 311 incorporates a lock on signal 311, a synchronisation signal 312, an optional configuration signal 313, and identification code 314, variable data 315 and an optional verification sequence 316.

As the method of the present invention may use the difference between times of transmission by the monitoring devices 100 fitted to each tyre, if the monitoring devices on different tyres transmit at the same time due to the fact that the monitoring device in each tyre is passing through the contact patch at the same time, this can make it difficult to identify transmissions from the different monitoring devices 100. It can be understood that the front tires have a longer travel distance than rear tires over a longer period of time. In the worst case scenario, this may occur at the start of a long relatively straight section of a journey and thus there will be little opportunity for variation due to differential wheel speeds during cornering. This can be dealt with by assigning a number of time slots for a transmission and incorporating a bit sequence in the transmission dataframe that is indicative of the selected time slot of transmission. For instance with a 5 bit sequence, 32 separate time slots can be assigned, each say 2 frame lengths apart, and a random number generator may be provided to determine which time slot will be selected for the next transmission. In this manner, the chances that two or more monitoring devices will transmit at identical times over a long period are minimised. Given that the chances of

simultaneous transmission are reduced, the time taken to identify the tyre each monitoring device 100 is fitted to is also reduced.

Additionally or alternatively, lower speed schemes with variable dataframe lengths can be used. Additionally, the length of the dataframe may be reduced for higher speeds. Furthermore at higher vehicle speeds an upper limit for the transmission interval can be defined to avoid excessive amount of transmissions. If exact timing information is required for say, wheel positioning, a bit sequence can be added to the dataframe to indicate how many revolutions have occurred since the last transmission. This also allows the car to calculate the total distance run by the tire since the last transmission. As an example, a 5 bit sequence and 20ms per revolution

(corresponding typically to a maximum speed of 250kmph) results in an increase of the transmission interval to 640ms.

It is of course to be understood that the invention is not to be limited to the details of the above embodiments which are described by way of example only.