Patent Description:
Pneumatic tyres are generally formed from rubber-based compounds which wear throughout the life of the tyre. The circumferentially extending portion of the tyre which is in contact with the ground during use is the tyre tread (and may alternatively be referred to as the tyre track) and generally includes grooves to allow water to be expelled from beneath the tyre. A minimum tread thickness may be defined for safety purposes and can be measured based upon the depth of the tread in a radial direction measured for example in a groove. In an automotive application a tyre may for example initially have a tread depth of <NUM> and be required to have a minimum thread depth of <NUM>. The rate of tread wear is variable but may for example be expected to provide a lifespan of at least <NUM>,<NUM> miles. In an aircraft application a tyre may for example have an initial tread depth of <NUM> and a minimum depth requirement of <NUM> and a tyre may last <NUM> to <NUM> landings.

In both automotive and aircraft applications it will be appreciated that tyre wear must be regularly monitored. This is generally a manual process requiring a user or maintenance operative to visually inspect and/or physically measure the depth of the tyre tread. Such checks should be carried out at regular intervals but even so since many factors contribute to the rate of tyre wear it can be difficult to predict when a change may be required.

Accordingly, there is a desire to provide systems and methods for monitoring tyre wear. In particular, it would be advantageous to provide systems and methods which can monitor tyre wear without, for example, requiring any instrumentation to be embedded within the tyre carcass. <CIT> discloses a method where circumference of a tire is used to estimate tire wear. <CIT> discloses a method where speed and load data are used to determine vehicle self-heating power, with a condition determined based on the self-heating power. <CIT> discloses a method of estimating tire state where wheel speed is measured, slip ratio rates are extracted, and a support vector data classification algorithm is applied to estimate a tire state. <CIT> discloses a method where vehicle speed, yaw rate, steering wheel angle, tire temperature/pressure/load, and vehicle mass, are measured, a current slip stiffness is determined, and a tread depth or change in tread depth is determined based on the slip stiffness.

A first aspect of the present invention, as defined in the appended claim <NUM>, provides an apparatus for monitoring the condition of a pneumatic tyre, the apparatus comprising: at least one pressure sensor to measure an internal pressure within the tyre; at least one speed sensor to measure a rotational speed of the tyre; and a controller that is configured to receive data from the pressure sensor and the speed sensor and output indications related to a condition of the tyre; the controller determining the output indications by: tracking the internal pressure with respect to time during use of the tyre; identifying at least one change in internal tyre pressure in a time interval between a first reference time and a second reference time, the reference times corresponding to points at which the speed sensor indicates different rotational speeds of the tyre, wherein one of the first reference time or the second reference time is selected to correspond to a time when the speed sensor indicates that the tyre is stationary, and the other of the first reference time and second reference time is selected to correspond to a local maximum rotational speed; and monitoring the pressure change as a function of rotational speed of the tyre to provide an indicator of tyre condition, for example tyre tread condition.

The inventors have recognised that changes or fluctuations in tyre pressure can be detected during operation which can in turn be directly related to the mass of the tyre. In normal use (and excluding for example a puncture or other tyre failure) the primary change in tyre mass can be expected to be a gradual decrease in mass as the tyre tread is worn away. Further, since the mass of the tread is at the outermost circumference of the tyre, the change in mass of the tread may have a particularly notable effect on the centripetal forces when the tyre is spinning. As such (and without being restricted to any particular theory) the inventors believe that some of the detected internal pressure changes may be related to the dynamic loads on the rotating tyre. In particular, the detected pressure within the tyre may be influenced by the rotational inertia of the tyre, with the tyre expanding at high speed and causing a drop in pressure. Therefore, the pressure in the tyre may be used as an indirect indicator of tyre mass. By monitoring pressure changes as a function of tyre rotational speed it may, therefore, be possible to indirectly monitor tyre wear.

One of the first reference time or the second reference time (defining the boundaries of the time interval) is selected to correspond to a time when the speed sensor indicates that the tyre is stationary. Thus, the pressure at one point of the interval may be a stationary tyre pressure. The other of the first reference time and second reference time is selected to correspond to a local maximum rotational speed. In other words, when defining the time interval the controller may seek an interval in which the tyre speed sensor indicates relatively high rotational acceleration or deceleration. As such, the first and second reference times may be selected to correspond to a relatively short-duration, but relatively high-magnitude, change in rotational speed. Selection of such a time interval may maximise the difference in dynamic loads on the tyre and thus sensitivity to the influence of tyre condition on detected pressure.

In some embodiments a maximum time duration for the interval may be pre-determined. Therefore, the controller may select a first reference time at which the tyre is stationary and seek a second point by finding the point of time at which the tyre has the maximum rotational speed within the pre-determined maximum time duration (either before or after the stationary time reference). In other examples the reference time may be selected as a local maximum rotational speed based upon the rotational speed being greater than a pre-determined threshold value. For example, in the case of an automotive tyre, a reference time may correspond to a point in time when the tyre rotation speed exceeds a nominal cruise speed (for example greater than 60mph). In the case of an aircraft tyre, a reference time may be selected based upon the tyre rotational speed being at or close to an expected speed at take-off.

The time interval between the first reference time and the second reference time may be selected to bound a sharp fluctuation in tyre pressure. For example, when tracking the internal pressure with respect to time during use of the tyre the controller may seek to identify such fluctuations and may then look up the corresponding tyre rotational speed to determine whether the time interval has a corresponding change of rotational speed.

Monitoring the pressure change as a function of rotational speed may comprise deriving a rate of change of pressure with respect to rotational speed of the tyre. For example, the pressure change per unit rotational speed may be determined. This may enable the comparison or trend monitoring of the rotation speed related pressure change (and may, for example, ensure that comparisons can be made without needing the rotational speeds to be identical). It may be appreciated that performing comparisons or trend monitoring may simplify implementations of embodiments, since the tyre condition trends may be identified from changes in the pressure change as a function of rotational speed without the need to correlate the detected changes to an actual tyre mass or tread thickness. For example, the controller may determine pressure change as a function of rotational speed each time a particular event happens (in the case of an aircraft this could be a take-off and in the case of an automobile this could be each time the vehicle stops). The change can then be compared over time to identify a trend and provide an operator with, for example, an estimate of the rate of tyre wear, or a warning that tyre wear may be greater than expected. As such, the control system may monitor the pressure change as a function of rotational speed by comparing the pressure change in a plurality of separate time intervals to identify trends in the pressure change as a function of rotational speed of the tyre.

When the pneumatic tyre is an aircraft tyre, the time interval may be after aircraft take-off. The inventors have found that a repeatably-detectable pressure fluctuation is found in this time period. It may be appreciated that at take-off the aircraft tyre is rotating at a maximum speed and becomes unloaded when the weight leaves the aircraft landing gear. Following take-off and before the landing gear is retracted it is standard practice to apply pre-retraction braking to stop the wheels rotating (for safety reasons it is generally undesirable to retract a spinning wheel). Thus, after take-off the aircraft wheel undergoes a relatively rapid deceleration. In embodiments of the invention the first reference time is after aircraft take-off when the wheels are unloaded and freely rotating. This is a local maximum wheel rotational speed. The second reference time may be when the wheels have been subjected to pre-retraction braking (and have for example fully stopped rotating).

According to a further aspect of the invention as defined in the appended claim <NUM>, there is provided an aircraft comprising an apparatus for monitoring the condition of a pneumatic tyre in accordance with embodiments described herein.

A further aspect of the invention, as defined in the appended claim <NUM>, comprises a method of monitoring wear in a pneumatic tyre, the method comprising:.

In some embodiments monitoring the pressure change as a function of rotational speed may comprise identifying trends in the function over a plurality of time intervals.

The tyre may be an aircraft tyre and the time interval may be between aircraft take-off and wheel retraction.

The method may further comprise transmitting data to a networked health monitoring system. A networked health monitoring system may monitor a number of vehicles and, as such, monitoring or trend monitoring may include a comparison of a plurality of vehicles having comparable pneumatic tyres. Such accumulated data may enable additional trend identification through computational analysis of large data sets.

Also disclosed is an apparatus for health-monitoring an aircraft wheel comprising a pneumatic tyre, the apparatus comprising: an internal tyre pressure sensor; a tachometer for measuring a rotational speed of the wheel; and a processor comprising: an input to receive data from the pressure sensor and tachometer; an output to send notifications related to tyre condition; and a machine-readable medium comprising instructions executable by the processor to: identify a minimum tyre pressure following aircraft take-off, when the rotational speed is at, or close to, a maximum; identify a stationary tyre pressure after said minimum, when the rotational speed indicates the wheel has stopped rotating; and derive a pressure difference, between the minimum tyre pressure and stationary tyre pressure, as a function of the rotational speed; and compare the pressure difference as a function of rotational speed over a plurality of take-off cycles to provide health monitoring of the tyre.

Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description or drawings.

A commercial aircraft <NUM>, in this case an example of the applicant's A320 family, is shown in <FIG>. The aircraft is provided with a nose landing gear <NUM> which carries a twin pair of wheels with pneumatic tyres and a pair of main landing gear <NUM> each having a further twin pair of wheels with pneumatic tyres. It may be appreciated that the particular configuration of wheels and landing gear will depend upon the aircraft configuration and is not limiting. For example, a main landing gear may also include multiple sets of twin wheels (as shown in the example of <FIG>) and such arrangements are common on larger aircraft. As noted above, tyres wear in use and must be monitored and replaced at regular intervals. This incurs operating costs and can be inconvenient if a tyre requires replacement at a time or location which is not suitable for the operator. As such it would be advantageous to provide an aircraft with a tyre monitoring system which could provide ongoing, and optionally live, monitoring of tyre wear such that aircraft operators may better schedule or anticipate tyre replacement needs.

<FIG> shows a more detailed schematic view of an aircraft main landing gear <NUM> and a tyre monitoring apparatus in accordance with an embodiment. The landing gear carries wheels each having a pneumatic tyre <NUM>. At the outer circumference of the tyre <NUM> is the tread <NUM> of the tyre, which has a tread depth "d" measured in a radial direction. Each wheel <NUM> may be provided with a rotational speed sensor <NUM>. The speed sensor <NUM> may for example be a tachometer. One known and reliable arrangement for a tachometer is to provide an electrical generator arrangement built into the axle of the wheel. By monitoring the output of the generator, the wheel rotational speed can be determined. It may be appreciated that such tachometers may already be provided on aircraft wheels for general wheel ground speed sensing. Each wheel is also provided with a tyre pressure sensor <NUM> for detecting the internal pressure of the associated tyre <NUM>. The pressure sensor <NUM> may be dedicated to the tyre monitoring apparatus of embodiments or may be part of a tyre pressure monitor system (which would also be used for detecting tyre punctures).

The apparatus further comprises a controller <NUM> which is in communication with the tyre pressure sensor <NUM> and tachometer <NUM>. It will be appreciated that whilst the figure only shows the controller <NUM> connected to the sensor <NUM> and tachometer <NUM> of a single wheel this is merely for clarity and the same controller <NUM> may monitor the tyres <NUM> on multiple wheels.

The controller <NUM> of the tyre monitor apparatus may be connected to an aircraft control system <NUM>. This may, for example, enable the controller <NUM> to track aircraft flight events (for example take-off, landing gear retraction) and may also enable the tyre monitoring apparatus to provide notifications to the aircraft systems (for example for the aircraft crew). It will be appreciated that in some embodiments the controller <NUM> may be integrated into other aircraft systems, such as the control system <NUM>, without altering the underlying operation of the apparatus.

The controller <NUM> of the tyre monitor apparatus may also be in communication with a health monitoring system <NUM>. The health monitoring system <NUM> may for example be a networked, or cloud-based, system. The health monitoring system <NUM> may connect to multiple systems and aircraft and may, for example, be used for fleet management and/or predictive maintenance. The connection to the health monitoring system <NUM> may be a wireless connection and may enable a live data or status feed to be sent from the controller <NUM>. Depending upon the particular configuration of the monitoring apparatus and health monitoring system <NUM>, it may be appreciated that the data exchanged across the network could either be raw data from the pressure sensors <NUM> and tachometer <NUM> or could be output from the tyre monitoring of the controller <NUM>. In the case where raw data is transmitted to the health monitoring system, it may be appreciated that the control <NUM> of the tyre monitoring apparatus may be a centralised networked controller (for example integrated into the health monitoring system).

A plot of tyre pressure versus time for an example aircraft flight cycle is shown in <FIG>. During the initial taxi and take off stage, the tyre pressure can be seen to gradually increase (the tyres are supporting the load of the aircraft and will heat under movement). The increase in pressure becomes steeper for the final stages of the take-off run due to the acceleration of the aircraft. During the cruise phase of the flight the tyre pressure is gradually dropping (the wheels are not in use and are subject to low ambient temperatures and pressures). Upon landing the tyres are subjected to an almost step change in pressure as they take the weight of the aircraft and undergo braking. Within this general pattern, the inventors have now identified a small but measurable localised pressure fluctuation which occurs immediately following take-off. This change can be clearly seen in <FIG> (but may be somewhat exaggerated for clarity) and is within approximately <NUM> secs immediately following take-off. The inventors have been able to identify this same fluctuation in pressure plots for a variety of flights and aircraft.

The detail of the localised pressure fluctuation is shown in <FIG>. As would be expected, the tyre pressure is at a peak <NUM> during take-off roll. When the wheels leave the ground they are freely spinning at a relatively high rotational speed and a brief pressure drop to a local minimum <NUM> can be detected by the controller <NUM>.

For safety reasons the wheels of at least the main landing gear <NUM> are braked prior to landing gear retraction. This is known as "pre-retraction" braking and is generally automatically triggered by a landing gear retraction command. The duration of the pre-retraction braking is relatively short, since it is undesirable to delay landing gear retraction. As such the wheels and tyres undergo a relatively rapid deceleration. When the tyre has been braked to a stop, the tyre pressure is found to partially recover to a second peak pressure <NUM>. This pressure is less than the peak <NUM> since the tyre has been unloaded since take-off and is cooling.

The inventors have recognised that the difference between the minimum pressure <NUM> measured when the wheel is rotating and the subsequent maximum <NUM> when the tyre has been stopped is a function of the rotational speed of the tyre and the mass of the tyre. As rotational speed may be measured from the tachometer <NUM>, it is possible for the controller <NUM> to quantify the change in pressure per unit of rotational speed. This removes the speed variable such that the function can be considered a direct indicator of the mass of the tyre. Variations in the mass of the tyre are primarily a result of tyre wear and tracking the change in mass (via the pressure change) can therefore be used as an indirect means of monitoring the tyre wear.

It may be appreciated that it is generally not necessary for the controller <NUM> to seek to calculate or derive the mass of the tyre <NUM> in order to implement the invention. Rather, the controller can seek to monitor general trends or changes in the pressure change as a function of tyre rotational speed (i.e. the change per unit rotation speed) detected at each take-off. The controller <NUM> may, for example, have access to historical data for a specific aircraft and tyre configuration to allow comparisons. The controller <NUM> may additionally or alternatively be provided with pre-determined threshold values, which have been identified as corresponding to certain tyre wear states (for example, partially worn, replacement required, etc). Such pre-determined threshold values could be defined empirically or theoretically or could be derived from large pressure profile data sets using an algorithm.

The method of embodiments of the invention are shown in the form of a flow chart in <FIG>. The first steps of the method comprise monitoring the internal pressure within an aircraft tyre in block <NUM> and monitoring the rotational speed of the tyre (or typically its associated wheel) in block <NUM>. It may be appreciated that an advantage of embodiments of the invention is that these monitoring steps may already be carried out on the aircraft for other purposes and, as such, the invention may be implemented without the need for additional dedicated equipment or sensors.

The acquired speed and pressure data can be tracked with respect to time and is therefore easy to correlate. In block <NUM> the controller seeks to identify within the acquired data a measured pressure change which corresponds to a related change in wheel rotational speed. In the case of an aircraft, the controller may be preconfigured to identify such a change occurring between take-off and landing gear retraction. In an automotive application, the controller may be configured to dynamically search the acquired data for suitable changes, for example which occur within a suitable time interval.

Once a suitable change in pressure and rotational speed is identified, in block <NUM> the method comprises determining the pressure change as a function of rotational speed, for example quantifying a ΔP per rpm.

In block <NUM>, the pressure change as a function of rotational speed is monitored, for example over multiple use cycles. This monitoring will generally include repeating the initial method steps (for example once per flight cycle or at a set time interval for an automotive application). Trends in the change of pressure as a function of rotational speed can then be used to identify the wear of the tyre. Over the life of the tyre the trends will be expected to show gradual change as the tread wears and reduces the mass of the tyre (and alters the mass distribution of the tyre). An alert or notification can be provided to an operator when threshold values are passed, which trend data suggests corresponds to a tyre requiring inspection or replacement. It will also be appreciated that, when monitoring trends, unexpected deviations may also be identified and could be flagged so that an operator can carry out additional inspection or maintenance, which may have preventative benefits.

It is to noted that the term "or" as used herein is to be interpreted to mean "and/or", unless expressly stated otherwise.

Although the invention has been described above with reference to preferred embodiments, it will be appreciated that various changes or modification may be made without departing from the scope of the invention as defined in the appended claims. For example, whilst the example above relates to an aircraft it will be appreciated that the basic principles of the invention may also be applicable to other vehicles in which it is desirable to monitor tyre wear.

Claim 1:
An apparatus for monitoring the condition of a pneumatic tyre (<NUM>), the apparatus comprising:
at least one pressure sensor (<NUM>) to measure an internal pressure within the tyre (<NUM>);
at least one speed sensor (<NUM>) to measure a rotational speed of the tyre (<NUM>); and
a controller (<NUM>) that is configured to receive data from the pressure sensor (<NUM>) and the speed sensor (<NUM>) and output indications related to a condition of the tyre (<NUM>); the controller (<NUM>) determining the output indications by:
tracking the internal pressure with respect to time during use of the tyre (<NUM>);
identifying at least one change in internal tyre pressure in a time interval between a first reference time and a second reference time, the reference times corresponding to points at which the speed sensor (<NUM>) indicates different rotational speeds of the tyre (<NUM>), characterized in that :
one of the
first reference time or the second reference time is selected to correspond to a time when the speed sensor (<NUM>) indicates that the tyre is stationary,
and the other of the first reference time and second reference time is selected to correspond to a local maximum rotational speed; and
monitoring the pressure change as a function of rotational speed of the tyre (<NUM>) to provide an indicator of tyre condition.