TYRE PRESSURE MEASUREMENT

Abstract: A device (11) which permits measurement of pressure and temperature of inflation air in a pneumatic tyre and wheel rim assembly (13, 15) so that the air pressure reading may be compensated for temperature. The device (11) has a body (19) attachable to the wheel rim (13). A stem (47) projects from the body and extends into the interior of the pneumatic tyre and wheel rim assembly (13, 15) through an opening (17) in the wheel rim. Mounted on the free end of the stem (47) is a temperature sensor (53) which is located remote from the wheel rim (13) when the body is attached thereto. An air passage (37, 49)in the body (19) communicates with the interior of the pneumatic tyre and wheel rim assembly (13, 15) when the body (19) is attached to the rim (13). Means (39) are provided to allow a pressure measuring means to be selectively connected to the device (11) for operative communication with the air passage (37, 49) so as to enable the pressure of the inflation air to be measured.

Description: "Tyre Pressure Measurement" THIS• INVENTION relates to the measurement of inflation air pressure in pneumatic tyre and wheel rim assemblies and in particular to a device which permits measurement of both the pressure and temperature of the inflation air whereby the pressure reading may be compensated for temperature. There is generally a prescribed pressure at which, or pressure range within which, a pneumatic tyre and wheel rim assembly should be operated for a certain load condi¬ tion on the tyre, and the pressure is usually specified at ambient atmospheric temperature. A pneumatic tyre heats up during operation and this leads to an increase in the pressure of inflation air within the tyre and wheel rim assembly. Because of this, it is necessary that the in¬ flation air pressure be either measured when the tyre is "cold" (i.e. at ambient atmospheric temperature) or, if measured when the tyre is "hot", adjusted to the corres¬ ponding pressure at ambient atmospheric temperature using the known gas law. The latter option is the most appro¬ priate way of measuring inflation air pressure in pneuma¬ tic tyre and wheel r.im assemblies in situations where vehicles are in almost constant operation 24 hours a day, such as in mining and transport operations. It is an object of this invention to provide a device which permits measurement of the pressure and temperature ' of inflation air in a pneumatic tyre and wheel rim assem¬ bly whereby the air pressure reading may be compensated for temperature. In one form the invention resides in a device which per¬ mits measurement of the pressure and temperature of infla¬ tion air in a pneumatic tyre and wheel rim assembly where¬ by the air pressure reading may be compensated for tem- perature, said device comprising a body having attachment means thereon for attaching it to the wheel rim, a member projecting from the body and adapted to extend into the interior of the tyre and wheel rim assembly, a temperature sensor mounted on said member whereby the temperature sensor is at a location remote from the wheel rim when the body is attached thereto, and pressure measurement ena¬ bling means adapted for communication with the interior of the pneumatic tyre and wheel rim assembly to enable mea¬ surement of the pressure of inflation air therein. Preferably, the temperature sensor is adapted to generate an electrical signal proportional to the temperature of the inflation air, and wherein the device further com¬ prises coupling means operable to couple the temperature sensor to temperature evaluation device adapted to receive and evaluate a signal received from the temperature sen¬ sor. Preferably the member projecting from the body comprises a stem and the temperature sensor is supported on the free end of the stem. Preferably the pressure measurement enabling means in¬ cludes an air passage in the body communicating with the interior of the pneumatic tyre and rim assembly by way of a port surrounding the stem. The attachment means may comprise a spigot adapted to extend through an opening in the wheel rim from one side thereof and retaining means for releasably engaging the spigot on the opposed side of the wheel rim so as to retain it in position. Preferably the body has a first bore co-axial with the spigot, the stem extending along the first bore in spaced relationship therewith whereby an air path is defined between the bore and the stem, said air path defining part of said air passage. The air passage preferably includes a second bore in the body communicating at one of its ends with the first bore and opening onto the exterior of the body at its other end, said second bore being adapted at said other end for connection to a valve stem. The body preferably includes first and second parts sea- lingly interconnected, said first bore extending through the second part and being closed at the end thereof remote from said port by the first part, said stem being mounted on the first part. The inflation air pressure may be measured using a pres¬ sure measurement means adapted to be operatively coupled to the valve stem on a selective basis so as to- rovide a measure of the inflation air pressure as required. The pressure measurement means may be in the form of an air pressure gauge or a pressure sensor capable of providing an output signal representative of air pressure, engagable with the valve stem. In another arrangement, a pressure sensor capable of providing an output signal representa¬ tive of the air pressure may be incorporated in the de¬ vice. The pressure reading at the recorded temperature is adjus¬ ted to a pressure value at ambient atmospheric tempera¬ ture. The pressure adjustment may be effected by means of a microprocessor device to which the output signals from the temperature and pressure sensors are fed. The invention will be better understood by reference to the following description of one specific embodiment thereof as shown in the accompanying drawings in which:- Fig. 1 is a fragmentary cross-sectional view illus¬ trating a device according to the embodiment mounted on a pneumatic tyre and wheel rim assembly; and Fig. 2 is an elevational view, in part section, of the device shown in Fig. 1. The embodiment shown in the drawings is directed to a device for use with pneumatic tyre and wheel rim assem¬ blies of heavy vehicles used in mining and transport operations. These vehicles are generally used almost continually 24 hours a day for 7 days a week, and only stop when it becomes necessary to service, or carry out maintenance on, the vehicles. Because of this, the tyres of the vehicles are not given an opportunity to cool down and hence it is difficult to obtain reliable measurements of inflation air pressure. It is desirable to carry out regular checks of inflation pressure so that the presence of any abnormal operating condition can be quickly esta¬ blished and appropriate action taken. The present inven¬ tion enables these checks to be carried out notwithstand¬ ing that the tyres are hot. Referring to the drawings, the device 11 is adapted for mounting on a wheel rim 13 which supports a pneumatic tyre 15. The rim 13 has the usual opening 17 which normally contains the conventional valve stem through which air is injected into the tyre and wheel rim assembly.. The device has a body 19 equipped with attachment means 21 for relea- sably attaching the body to the wheel rim 13. The attach¬ ment means 21 comprises an externally threaded spigot 23 and retaining means 25 in the form of a nut threadably engagable with the spigot. The spigot 23 is adapted to be received in the hole 17 in the rim from one side thereof with the retaining means engaging the spigot on the other side of the rim so as to secure the body to the rim. A rubber grommet 27 provides an air tight seal between the rim 13 and the spigot 23. The body 19 includes first and second parts 29 and 31 respectively which are in sealing engagement with each- other and fixed together by machine screws 33 or any other suitable fixing means. The second part 31 is in the form of a so-called T-spud. A first bore 35 is co-axial with the spigot 23 and extends through the second part 31 of the body. Transverse to and communicating with the first bore 35 are a pair of further bores 37 each of which opens onto the exterior face of the second part 31 of the body. The outer end portion of each further bore 37 is inter¬ nally threaded whereby either one of the further bores may threadingly engage one end of a valve extension 39. The particular bore 37 not engagement with the extension 39 is closed by a removable plug 41 threadingly engaged there¬ with. With the two bores 37, the extension 39 may be connected to either side of the body 19 according to whether the device 11 is fitted to a pneumatic tyre and wheel rim assembly on the right or left hand side of a vehicle. The extension 39 is of convention construction, having a central bore fitted with a valve core (not shown) and a connector 43 at the free end thereof adapted to be engaged by an air chuck to facilitate injection of inflation air in the pneumatic tyre and wheel rim assembly. A removable valve cap 45 is provided for the connector 43. A stem 47 extends from the body 19 through the bore 35 in the spigot 23. The stem 47 is of smaller cross-sectional size than the bore 35 whereby an air path 49 is defined between the bore and the stem. The air path 49 has a port 51 at its outer end via which the air path communicates with the interior of the pneumatic tyre and wheel rim assembly when the device is in position thereon. The air path 49 and the particular bore 37 communicating with the valve extension 39 define an air passage in the body 19. The stem 47 is mounted at its inner end on the first part 29 of the body and carries a temperature sensor 53 at its outer end. The stem is of such length that the tempera¬ ture sensor 53 is remote from the rim 13 when the device is mounted thereon. In this way, the temperature sensor is able to sense the temperature of inflation air within the pneumatic tyre and wheel rim assembly and not the temperature of the wheel rim itself. The temperature sensor 53 is arranged to generate an electrical signal proportional to the temperature of inflation air and is coupled by way of an electrical cable 55 to a connector 57 which is mounted on a bracket 59 carried by the extension 39. The tyre may be inflated or deflated in the conventional way through the extension 39. When it is desired to check the pressure of inflation air within the tyre in circum¬ stances where the tyre is hot, a pressure measuring device is coupled to the extension in the usual way to provide a reading of the tyre air pressure and a temperature evalua¬ tion device (not shown) is coupled to the connector 57 so as to receive and evaluate a signal generated by the temperature sensor 53. The pressure measuring device may be of any suitable form, such as a conventional tyre pressure gauge which provides a visual indication of tyre pressure or a pressure sensing device which generates an electrical signal representative of air pressure. From the recorded temperature and pressure readings of inflation air within the pneumatic tyre and wheel rim assembly, the corresponding pressure when the tyre is "cold" may be calculated using the known gas law. The recorded temperature and pressure readings may be proces¬ sed manually, but it is preferable that the readings be processed using a microprocessing device into which sig- nals representative of the tyre pressure and temperature are fed directly from the respective sensors. Preferably, the microprocessing device has facilities for entering into memory certain information concerning each tyre including the desired operating pressure so that it can evaluate, and provide a reading of, any discrepancy bet¬ ween the actual tyre pressure compensated for temperature and the desired tyre pressure. The microprocessing device may also have provision for entering information such as tyre tread depth and distance travelled by the vehicle. The microprocessing device may have provision for connec¬ tion to a printer so that a print out of the various results may be obtained as required, or the micropro¬ cessing device may interface with another computer to analyse the results directly. An important, although not essential, feature of the device according to this embodiment is the arrangement whereby the stem 47 is supported on the first part 39 of the body and located in the bore 35 formed in the second part 41 of the body. This relatively simple arrangement not only provides the device, when mounted on the rim, with access to the interior of the tyre via the stem, but also permits the device to be constructed using many standard components which are available "off the shelf". In another arrangement (not shown), the device is equipped with a pressure sensor which generates a signal propor¬ tional to the inflation air pressure. This arrangement eliminates the need to couple a pressure measuring device to the extension 39 in the manner described with the first embodiment. The pressure sensor is electrically coupled to a connector to which a pressure evaluation device may be coupled so as to receive and evaluate a signal genera¬ ted by the pressure sensor. With this arrangement, sig¬ nals representative of the temperature and pressure of the inflation air may be fed directly into the microprocessing device. It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described. For instance, with the device according to the first embodiment, the microprocessing device can only be coupled thereto when the vehicle is not- in operation. In an alternative arrangement, the device according to the invention may incorporate means for wireless transmission of signals representative of the operating pressure and temperature of the inflation air in the pneumatic tyre and wheel rim assembly to a remote receiving means. In this way, temperature compensated pressure readings may be obtained even when the vehicle is in operation. The remote receiving means may be mounted on a part of the vehicle such as in the operator's cab or at a receiving station remote from the vehicle.

Claims: THE CLAIMS defining the invention are as follows:- 1. .A device which permits measurement of pressure and temperature of inflation air in a pneumatic tyre and wheel rim assembly whereby the air pressure reading may be compensated for temperature, said device comprising a body having attachment means thereon for attaching it to the wheel rim, a member projecting from the body and adapted to extend into the interior of the tyre and wheel rim assembly, a temperature sensor mounted on said member whereby the temperature sensor is at a locaton remote from said rim when the body is attached thereto, and pressure measurement enabling means adapted for communication with the interior of the pneumatic tyre and wheel rim assembly to enable measurement of the pressure of the inflation air. 2. A device according to claim 1 wherein the temperature sensor is adapted to generate an electrical signal propor¬ tional to the temperature of the inflation air and wherein the device further comprises coupling means operable to couple the temperature sensor to a temperature evaluation device adapted to receive and evaluate a signal from the temperature sensor. 3. A device according to claim 1 or 2 wherein the mem¬ ber • projecting from the body comprises a stem and wherein the temperature sensor is supported on the free end of the stem. 4. A device according to claim 3 wherein said pressure measurement enabling means includes an air passage in the body arranged for communication with the interior of the pneumatic tyre and rim assembly by means of a port sur¬ rounding the stem. 5. A device according to claim 4 wherein said pressure measurement enabling means further comprises a valve stem having a bore therein communicating at one end with the air passage in the body and being adapted at its other end for connection to a pressure measuring means. 6. A device according to claim 4 wherein said pressure measurement enabling means comprises a pressure sensor responsive to air pressure in the pneumatic tyre and rim assembly, said pressure sensor being mounted on the body for operative communication with the interior of said pneumatic tyre and rim assembly. 7. A device according to any one of the preceding claims wherein the attachment means comprises a spigot adapted to extend through an opening in the wheel rim from one side thereof and retaining means for releasably engaging the spigot on the opposed side of the rim so as to retain it in position. 8. A device according to claim 7 wherein the body has a first bore co-axial with the spigot, the stem extending through the first bore in spaced relationship therewith whereby an air path is defined between the bore and the stem, said air path defining part of the air passage in the body. 9. A device according to claim 8 wherein said air pas¬ sage includes a second bore in the body communicating at one end with the first bore and at the other end opening onto the exterior of the body, said second bore being adapted at said other end for connection to the valve stem. 10. A device according to claim 9 wherein the body in¬ cludes first and second parts sealingly interconnected. said first bore extending through the second part and being closed at the end thereof remote from the port by means of a first part, said stem being mounted on the first part. 11. A device substantially hereindescribed with reference to the accompanying drawings.

Inventors: CREIGHTON DOUGLAS JOHN, MOORE IAN MCKENZIE, CREIGHTON, DOUGLAS, JOHN, MOORE, IAN, MCKENZIE
Applicants: OTRACO INT, OTRACO (INTERNATIONAL) PTY. LTD.
Application year: 1985
Main classification: B60C23
IPC codes: B60C23