Tyre inflation pressure control system

0001The invention relates to a tyre inflation pressure control system comprising a vehicle wheel having a rim with a tyre mounted thereon and an air reservoir, the system further comprising a decant valve for allowing air to transfer from the reservoir into the tyre, a deflate valve for deflating the tyre, a valve control unit fixed relative to the wheel and a controller fixed relative to the vehicle and which can communicate with the valve control unit.

0002The inflation pressure of vehicle tyres is known to be a contributory factor in the tyre wear, the grip provided by the tyre and the fuel consumption of the vehicle. By reducing the pressure of the tyre the contact surface with the ground is increased thereby improving the grip and which allows a greater power to be transmitted between the vehicle and the ground. This is particularly advantageous in slippery conditions caused by ice or mud for example. Furthermore, when utility vehicles such as tractors operate in wet fields, the power which can be transmitted to the ground is limited and this can be increased by reducing the tyre pressure.

0003However an increase in contact surface results in an increase in tyre wear and, as is particularly apparent on hard surfaces at speed, an increase in fuel consumption. Therefore it is recognised that optimum performance of the vehicle is achieved with different tyre inflation pressures for different operating conditions. This has led to the development of automatic inflation and deflation arrangements which allow the tyre inflation pressure to be changed during operation to optimise the driving characteristics described above.

0004German Utility Model <patcit id="pcit0001" dnum="DE29718420U1"><text>DE 29718420 U1</text></patcit> describes a tyre pressure control system wherein a wheel comprises an integrated compressed air reservoir located on the rim and surrounded by the tyre. Air is transferred from the reservoir to the tyre by means of a valve so as to inflate the tyre when required. The tyre is deflated via the same valve by transferring air to the environment. A control device is also located between the rim and the tyre and serves to control the valve means thereby inflating and deflating the tyre. The tyre pressure is maintained at a set point by the control device automatically activating the valve means in response to a measured distance between the rim and the tyre. The disclosed system does not allow active control of the tyre pressure and serves merely to maintain the pressure at a predetermined value.

0005United States patent application published as <patcit id="pcit0002" dnum="US20050081973A"><text>US-2005/0081973</text></patcit> describes a wheel assembly having a tyre mounted upon a rim. A reservoir disposed on the wheel stores gas under pressure for inflating the tyre. A solenoid valve provides a connection between the reservoir and the closed space of the tyre for inflating the tyre. A further solenoid valve provides a connection between the closed space and the atmosphere for deflating the tyre. A data processor which does not rotate with the rim communicates with a controller which does rotate with the rim. The controller feeds electrical signals to the solenoid valves to make them switch.

0006There is a desire to reduce the power consumption of the valve controller which rotates with the wheel, especially when a local power supply is employed such as a battery fixed relative to the wheel. Achieving access to the battery for replacement thereof can be difficult and time consuming.

0007In accordance with the invention there is provided a tyre inflation pressure control system comprising a vehicle wheel having a rim with a tyre mounted thereon and an air reservoir, the system further comprising a decant valve for allowing air to transfer from the reservoir into the tyre, a deflate valve for deflating the tyre, a valve control unit fixed relative to the wheel and a controller fixed relative to the vehicle and which can communicate with the valve control unit, <b>characterised in that</b> the decant and/or the deflate valve is a check valve which is opened by a pilot pressure sourced from the reservoir and wherein the pilot pressure is applied to the decant and/or deflate valve via a respective piezoelectric controlled valve which are in communication with the valve control unit. Advantageously, by using piezoelectric valves to preselect the decant and/or deflate valves the energy consumption is reduced because the valve required to regulate a pilot pressure is smaller than the directional control valve employed in <patcit id="pcit0003" dnum="DE29718420"><text>DE29718420</text></patcit> or the solenoid valves employed in the system of <patcit id="pcit0004" dnum="US20050081973A"><text>US-2005/0081973</text></patcit> for example.

0008In a preferred arrangement the controller can communicate wirelessly with the valve control unit. By providing a wireless link between the valve control unit and the controller the tyre inflation pressure can be actively controlled by a driver or automatically by the vehicle control system. Therefore control of the tyre inflation pressure can be integrated with other controls of the vehicle.

0009The inclusion of the air reservoir on the vehicle wheel allows any adjustment in the tyre pressure to be swift wherein the pressure in the air reservoir is significantly greater than the tyre pressure. Preferably the air reservoir is located within the tyre volume and is preferably toroidal in shape and mounted to the rim thereby remaining within the conventional profile of the wheel. The air reservoir is preferably of a substantially fixed volume which may be provided by forming the reservoir of rubber material which is preferably reinforced. By fixing the volume of the air reservoir and forming it within the volume of the tyre the effective inflatable volume of the tyre is reduced thereby decreasing the time taken to adjust the inflation pressure.

0010The system preferably further comprises a pressure sensor in each of the tyre volume and the reservoir volume wherein each pressure sensor is in communication with the valve control unit by a wired link for example. This allows continuous monitoring of the two chambers comprising pressurised air. The pressure information can be fed wirelessly to the controller to facilitate active management of the tyre inflation pressure.

0011The system may further comprise an air pressure source associated with the vehicle and from which air is transferred to the reservoir via a valve which is in communication with the controller. In this arrangement the reservoir can be maintained at an operating pressure by pumping air from a pressure source located on the vehicle chassis for example. Preferably the air is transferred to the reservoir via a rotary transfer arrangement which is associated with a wheel mounting hub. The air pressure source may be provided by an air pump located on the vehicle which may also supply air to a brake system for example. Due to the presence of the reservoir on the wheel, advantageously only a single pipe is required between the vehicle and the wheel via the rotary transfer arrangement.

0012The valve control unit associated with the wheel is preferably powered by a battery which is fixed relative to the wheel, for example in the volume defined by the tyre. In the case where piezoelectric valves are employed the power consumption of the battery is reduced thereby demanding a lower battery capacity. However when in a closed system with no electrical connections beyond the wheel assembly the battery is preferably recharged by a generator module which exploits the kinetic energy available within the apparatus. The generator module may comprise an air turbine which is also fixed relative to the wheel. In a first arrangement the turbine may be driven by air exiting the tyre during deflation via the deflate valve. Advantageously this exploits the kinetic energy of air which would otherwise be expelled unimpeded to the environment.

0013In a second arrangement the turbine is driven by air exiting the reservoir. In this case the system preferably further comprises a recharge valve which allows air to transfer from the reservoir to the environment via the turbine, the recharge valve being a check valve which is opened by a pilot pressure sourced from the reservoir and applied via a piezoelectric valve which is in communication with the valve control unit. Advantageously this arrangement exploits the potential energy within the pressurised reservoir and can be employed to recharge the battery upon demand and does not rely on deflation of the tyre. Preferably the stored energy in the battery is monitored and the recharge valve is operated automatically in response to the energy falling below a predetermined threshold.

0014In a third arrangement the turbine is driven by air being transferred to the reservoir. In the case where the system comprises an air pressure source associated with the vehicle, then the turbine may be connected between the source and the reservoir so as to charge the battery whenever air is transferred across the interface between the vehicle and the wheel. This composition advantageously requires no additional recharge valve. In addition, the charging of the battery can be provided independent from decant/inflate process.

0015In an alternative arrangement the generator module may comprise a dynamo which is driven by the rotation of the wheel and is arranged to recharge the battery.

0016The invention is particularly beneficial when applied to a tractor which operates in conditions which vary widely and frequently.

0017Further advantages of the invention will become apparent from the following description of specific embodiments with reference to the drawings in which:- <dl id="dl0001"><dt>Figure 1</dt><dd>is a schematic diagram of a tyre inflation pressure control system in accordance with a first embodiment of the invention;</dd><dt>Figure 2</dt><dd>is a schematic diagram of a tyre inflation pressure control system in accordance with a second embodiment of the invention;</dd><dt>Figure 3</dt><dd>is a schematic diagram of a tyre inflation pressure control system in accordance with a third embodiment of the invention; and</dd><dt>Figure 4</dt><dd>is a schematic diagram of a tyre inflation pressure control system in accordance with a fourth embodiment of the invention.</dd></dl>

0018In accordance with a first embodiment of the invention a tractor comprises a chassis designated generally at 10 and a wheel designated generally at 12. It should be understood that <figref idref="f0001">Figure 1</figref> is highly schematic and features located within dashed box 10 are located anywhere on the tractor whereas those features within dashed box 12 are integrated with the wheel and rotate therewith. Furthermore the tractor comprises at least four wheels wherein two or maybe four have the same construction as described below with reference to wheel 12.

0019The wheel 12 comprises a generally cylindrical rim (not shown) upon which a tubeless tyre is mounted. A toroidal air reservoir 14 formed of reinforced rubber is disposed on the wheel rim within the volume defined by the tyre. Therefore the air reservoir forms an inner chamber 14 of pressurised air and the tyre forms an outer chamber 16. The volume of the air reservoir 14 is substantially fixed due to the reinforcement of the rubber material. Therefore deformation of the material between the air reservoir and the tyre volume does not occur when significant pressure differences arise between the chambers 14,16.

0020The volume of air reservoir 14 is in the region of 320 litres and the inflatable volume of tyre 16 is in the region of 490 litres. The maximum operating pressure of the air reservoir is around 6 bar whereas the operating pressure of the tyre 16 typically varies between 0.8 and 2 bar.

0021It should be appreciated that for trailers (e.g. muck trailers) this maximum tyre pressure is around 4 bar and that different vehicles require different inflation pressures.

0022The system comprises a decant valve 18 and a deflate valve 20 each of which is a pilot controlled check valve. Decant valve 18 is located in a fluid transfer line between the air reservoir 14 and tyre 16. Deflate valve 20 is located in a fluid transfer line between the tyre 16 and the environment.

0023Each check valve 18, 20 has associated therewith a piezoelectric control valve. A first piezoelectric valve 22 controls the delivery of a pilot pressure taken from air reservoir 14 to decant valve 18 via pilot line 24. A second piezoelectric control valve 26 controls the delivery of a pilot pressure also from air reservoir 14 to the deflate valve 20 via pilot line 28. Each piezoelectric valve 22, 26 is activated by a valve control unit 30 employing electrical signals sent via respective lines 31,32.

0024The significantly larger pressure of air reservoir 14 keeps decant valve 18 in a closed position in normal operation. By activation of piezoelectric valve 22 a pilot pressure opens decant valve 18 and allows air to transfer into tyre volume 16 thus increasing the pressure therein.

0025During normal operation the pressure within tyre 16 maintains deflate valve 20 in the closed position. Upon activation of piezoelectric valve 26 a pilot pressure forces deflate valve into an open position thereby allowing air to exit tyre volume 16 thus causing a reduction in the pressure thereof.

0026Each chamber 14,16 comprises a respective pressure relief valve 34a,34b which can be preset to relieve the pressure within the respective chamber when it exceeds a predetermined value.

0027Furthermore each chamber 14,16 has associated therewith a pressure sensor 35a,35b each with a respective wired link to valve control unit 30. Each pressure sensor 35a,35b senses the pressure in the associated volume and transmits this information to the valve control unit 30.

0028A rechargeable battery 36 is arranged within the wheel assembly 12 so as to power the valve control unit 30. However, in an alternative arrangement, the battery may be replaced with a capacitor which can deliver a high current and be charged over a short period. Apparatus to charge the battery 36 will be described in more detail below.

0029The pressure control system further comprises a controller 40 located on the tractor chassis 10. The controller 40 is in wireless and bidirectional communication with valve control unit 30 in accordance with the invention by a wireless link. The controller 40 is also in communication with a tractor management system 50 which serves to monitor and control various operating parameters of the tractor such as speed, wheel slip and transmission ratio for example.

0030An air pressure source 52 is provided by an air pump which is located on the tractor. The air source 52 can supply pressurised air via an electric valve 54 and a rotary transfer arrangement 56 and check valve 58 to the reservoir 14. The valve 54 is controlled via a wired link by the controller 40. The rotary transfer arrangement 56 is of a known construction such as that disclosed in <patcit id="pcit0005" dnum="US6439044B"><text>US-6,439,044</text></patcit> by way of example only. This allows pressurised air to be transferred from the chassis 10 to the rotating wheel assembly 12.

0031An example sequence of operation will now be described with reference to <figref idref="f0001">Figure 1</figref>. The pressures within reservoir 14 and tyre 16 are sensed by pressure sensors 35a,35b and communicated to tractor management system 50 via valve control unit 30, wireless link 42 and controller 40. This information may be displayed to the driver. Commands from the driver are entered into the tractor management system 50 via a user interface (not shown).

0032Commands are then communicated to controller 40 which then passes the command to valve control unit 30 via wireless link 42.

0033The target pressure is stored locally on the wheel by the valve control unit 30. This value is updated by the controller 40 via the wireless link periodically and/or when a change demand occurs.

0034In the case of the sensed pressure being below the target pressure, valve control unit 30 activates piezoelectric valve 26 by an electric signal sent by line 32. Piezoelectric valve 26 is activated for a predetermined duration of say 5 seconds which causes deflate valve 20 to open thereby reducing the pressure in tyre 16. The pressure sensed in tyre 16 is then compared to the commanded pressure and, if further deflation is required, piezoelectric valve 26 is activated for another period.

0035It should be understood that the duration at which the piezoelectric valves 22,26 are activated may be determined by an algorithm which takes into account the existing pressure in chambers 14,16 and the target pressure of tyre 16. Alternatively, real time adjustment may be employed to set the inflation pressure at the desired value by constant measuring of the pressure in combination with control of the decant process.

0036During operation valve control unit 30 continually monitors the pressure within tyre 16 and compares it to the target pressure and activate the piezoelectric valves 22,26 accordingly.

0037The above described control and monitoring of the inflation pressure is executed on a local basis at the wheel by the valve control unit 30. By only updating the target pressure when a change is required (either demanded manually by the driver or automatically via the management system 50) the number of messages passing over the wireless link 42 is minimised. Advantageously this reduces the energy consumption of the battery 36 and avoids unreliable control caused by discontinuities in the wireless connection 42.

0038It is envisaged, however, that control and monitoring of the inflation pressure may be done instead by the controller 40 via wireless link 42 wherein valve control unit 30 simply serves to pass on the sensed parameters and control the valves 22, 26 as demanded. The target inflation pressure in this case is stored by the controller 40 or management system 50.

0039In the case where the sensed pressure within air reservoir 14 drops below a predetermined threshold, valve control unit 30 commands a top-up action to controller 40 via wireless link 42. Such a command triggers activation of piezoelectric valve 54 which transfers air under pressure from air source 52 to air reservoir 14 until the target pressure is obtained.

0040With reference to <figref idref="f0002">Figure 2</figref>, a generator module is provided to recharge the battery 36 by exploiting the available energy of the pressurised air in the fluid system. A turbine 60 is disposed in the air stream of the air which is expelled upon deflation from tyre 16. The turbine 60 powers generator G which serves to recharge battery 36 thereby increasing the lifetime thereof.

0041In an alternative arrangement shown in <figref idref="f0003">Figure 3</figref>, a turbine 62 is located in a dedicate air stream between the reservoir 14 and the environment. A check valve 64 regulates the expulsion of air through the turbine 62 and is opened by a pilot pressure sourced from the reservoir 14 and applied via a piezoelectric valve 66 which is in communication with the valve control unit 30. In this arrangement the valve control unit 30 can activate valve 66 when the electrical energy in the battery 36 is sensed to be below a predetermined threshold. Therefore generator G can be activated upon demand and does not rely on a deflation step as per the embodiment of <figref idref="f0002">Figure 2</figref>.

0042In yet another alternative arrangement shown in <figref idref="f0004">Figure 4</figref>, a turbine 68 is connected in the air stream between the rotary transfer arrangement 56 and the reservoir 14. In a similar manner to that of <figref idref="f0002">Figures 2</figref> and <figref idref="f0003">3</figref>, the turbine 68 powers a generator G which serves to recharge battery 36. However, in this case, the turbine 68 is driven each occasion air is transferred from the vehicle air supply 52 to the reservoir 14. Furthermore, there is no requirement for further valves to direct airflow through the turbine. In addition, the charging of the battery can be provided independent from decant/inflate process. The presence of the pressure relief valve 34a associated with reservoir 14, allows air to be transferred from the vehicle 10 to the reservoir 14 whenever a charging of the battery 36 is required and without affecting the other parts of the system.

0043In a further alternative (not shown), the turbine may be replaced by a dynamo which is driven by the mechanical rotation of wheel 12.

0044In summary there is provided a tyre inflation pressure control system comprising a vehicle wheel having a rim with a tyre mounted thereon and an air reservoir. The system further comprises a decant valve for allowing air to transfer from the reservoir into the tyre and a deflate valve for deflating the tyre. A valve control unit fixed relative to the wheel is in communication with a controller which is fixed relative to the vehicle. By providing a highpressure reservoir on the wheel assembly and means to control the associated distribution valves remotely, only a single feed through connection is required for air supply from the vehicle. The decant and/or the deflate valve is a check valve which is opened by a pilot pressure sourced from the reservoir. The pilot pressure is applied to the decant and/or deflate valve via a respective piezoelectric controlled valve which are in communication with the valve control unit.

0045From reading the present disclosure, other modification will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of tyre inflation systems and component parts therefore and which may be used instead of or in addition to features already described herein.