METHOD AND APPARATUS FOR TYRE PRESSURE DETERMINATION

Abstract: Method and apparatus for tyre pressure determination, for example off-vehicle during inflation on a tyre changer, is based upon impact vibrational input and corresponding waveform generation by a piezoelectric cable transducer. Analysis of the waveform output on a frequency or time-base shift with respect to pressure provides a basis for numerical pressure determination based on identification of dominant peaks. Repeated constant level impacts by a solenoid-operated hammer device during inflation enables monitoring of the dominant peak and thus inflation pressure.

Description: METHOD AND APPARATUS FOR TYRE PRESSURE DETERMINATION This invention relates to a method and apparatus for tyre pressure determination. Prior proposals in the field of tyre pressure determination include our own published European application EP 0 756 167A (our reference P52740EP) which discloses a technique of tyre evaluation, including pressure determination based upon the use of an ultrasonic waveform and assessment of the tyre on the basis of monitoring the attenuation of such a waveform. There is disclosed in US 8 111 321A (Nasa) apparently filed 23 August 1993 and carrying a further date (which may be the patent grant date, but that is not clear) of 1 March 1994, a remote tire pressure sensing technique. In the disclosed embodiment, vibration inducing means in the form of a hammer is used to produce an impact with a tire to which is attached vibration detecting means in the form of an accelerometer which is secured to the tread of the tyre by double sided tape. Vibration measuring means is connected to the accelerometer, and is in the form of a computer frequency analyser (apparently a personal computer, judging from the drawing) . Tire pressure is determined by the frequency analyser. Such an analysis is based on the fact that the accelerometer measures radial acceleration and does so at "the best location" which is "the tread area" . The frequency analyser correlates vibration frequency peaks to tire pressure. If the above US patent application was published prior to the priority date of the present application, the present applicants were unaware of it but in any case the present invention can take as its technical starting point the disclosure in the above US 321 specification on the basis that we have discovered that tire pressure can be readily determined on a simple and .easily-analysed basis by use of a transducer which employs a length of piezo-electric cable to generate a signal and waveform from the energy input to the tire and/or rim. In this way, we have discovered, an extremely simple and inexpensive transducer is able to generate a waveform which includes dominant peaks which themselves enable relatively simple analysis for tire pressure determination. In contrast, the device of the US 321 specification, by virtue of its use of an accelerometer as the transducer to produce the signal from which tire pressure is determined, requires relatively sophisticated spectral analysis apparatus in order to achieve a numerical value for the tire pressure. Accordingly, an object of the present invention is to provide a method and apparatus for tire pressure determination offering improvements in relation to one or more of the matters discussed above in relation to the US 321 specification, or indeed generally. Further alternatives and more specific objects of the embodiments of the invention include provision of means for direct tire pressure determination which is conveniently applicable at times of tire inflation, and to provide a method and apparatus particularly applicable to tire pressure measurement with a tire off-vehicle, for example such that the measurement can conveniently be made while the tire is on a tire changer, during inflation and without halting the inflation process. According to the invention there is provided a method and apparatus for tyre pressure determination, as defined in the accompanying claims. In an embodiment of the invention a tyre is subjected to energy input and generates a corresponding energy waveform output and the waveform is analysed o determine tyre pressure. For this purpose, the energy input to the tyre is by means of a vibrational or acoustic input and the generation of the corresponding energy waveform output from the tyre is effected by means of a piezo-electric cable transducer, and the analysis of tyre pressure is carried out by reference to the waveform generated by the cable. By providing tyre pressure data in electrical waveform format, the embodiments of the invention are able to take advantage of cost-and-time- effective data analysis systems which are able to generate numerical tyre pressure output figures in convenient format. The embodiments employ a mechanical impact device for energy input to the tyre, this being achieved utilising a convex-curved impact device associated with means for controlling the extent of the energy input to the tyre, whereby consistency of input can be achieved as a basis for a systematic approach to correlation and calibration of the output waveform data with respect to tyre pressure. In the embodiments, the transducer for generation of the energy waveform from the tyre is a piezo- electric cable. The cable is mounted in physical contact with the tyre sidewall, for example by means of a mechanical holding device. The piezo-cable produces a particularly satisfactory and characteristic voltage waveform output which can be analysed on a frequency shift basis or on a time-base shift basis for calculation of the corresponding tyre pressure. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which : Fig 1 shows a flow diagram illustrating the energy input by a hammer or ball device to the tyre and/or rim assembly, the piezo-cable taped to the tyre or rim producing a voltage which is analysed for dominant peaks and by reference to frequency and/or time domain shifts the apparatus is calibrated numerically in tyre pressure; Fig 2 shows plots of frequency against pressure for a range of identified automotive tyres, the frequencies plotted being those of the dominant peak obtained from a transducer connected to the tyre; Fig 3 shows further similar plots of frequency against pressure for a particular range of tyres; and Fig 4 shows a still further plot of frequency against pressure for a still further range of tyres. As shown in Fig 1, a method 10 of tyre pressure determination comprises subjecting a tyre to energy input by an impact device providing mechanical impact with a tyre or with its associated wheel and/or rim. This step is provided by means of a controllable energy input device 12 which may be in the form of a constant height or angle hammer device 14 or a constant height ball bearing device 16, both of which are, in use, disposed so that the impact object (the hammer or the ball bearing) falls on the tyre or the wheel/rim assembly 18. In accordance with the next step of the method 10, a corresponding energy waveform output from the tyre is provided by means of electrical transducer means constituted by a length of piezo-electric cable 20. The piezo-electric cable 20 is connected to voltage analysis means 22 which is adapted to determine tyre pressure by reference to the waveform generated by the piezo-electric cable. Voltage analysis means 22 performs the step 24 of identifying frequency and/or time domain shifts of the dominant peaks in the electromotive force (emf) generated by the piezo-electric cable. The system is calibrated, as shown at step 26, numerically in terms of tyre pressure. This is achieved on the basis of frequency calibration against known tyre pressure data. Summarising therefore in relation to Fig 1, it can be seen that the method 10 comprises a controllable energy input 12 using the hammer device 14 or a ball bearing device 16 to apply an energy input to the tyre or wheel/rim assembly 18 in contact with which is taped the piezo-electric cable 20 which produces a signal voltage which is processed by analysis means 22 which identifies frequency or time domain shifts with respect to tyre pressure and is calibrated in suitable units such as pounds per square inch or bars. In the embodiments, the wheel and tyre assembly 18 was attached to a wheel balancer (not shown) , and a length of piezo-cable 20 was attached to the tyre rim with adhesive tape. The piezo-cable was then electrically connected to a storage oscilloscope and the tyre was subjected to energy input by means of an impact with a small ball peen hammer (14) which was caused to make impact with the tyre by means of a pivoting fall from a predetermined height - see controllable energy input device 12 of Fig 1. The hammer may be as in Fig 1 of the US 321 reference but preferably with a convex hammerhead. For each impact of the hammer device 14 with the tyre/wheel rim assembly 18, the dominant voltage peak was noted on the oscilloscope and recorded for analysis purposes. The tests were repeated at a graded series of different tyre pressures using otherwise constant test conditions, including energy input. The results of these tests are shown in Figs 2 , 3 and 4. Several series of tests were carried out utilising impact with the tyre tread and with the tyre sidewall and with the wheel/rim assembly. Likewise, tests were carried out with the piezo-cable transducer device secured firstly to the tyre wheel/rim assembly and secondly to the tyre sidewall itself. Satisfactory results were achieved from each series of tests. Both time and frequency domain shifts were noted for the dominant voltage peak produced by the transducer device upon impact. Further tests were carried out using a steel ball dropped from a constant height in place of the hammer, thereby enabling a more accurately controllable input of energy to the tyre. Both energy input systems yielded results which could be readily interpreted in terms of tyre pressure. The test procedures were carried out on a range of tyre pressures from 0 psi to 45 psi in steps of 5 psi. From tests carried out with impacts on all the available tyre faces, it was found that the tyre wall provided the best results (in contrast to the US 321 reference) because this part of the tyre has very little reinforcement compared to the other parts, such as the tread. The oscilloscope showed a readily identifiable single peak that moved up the frequency scale with increasing tyre pressure, and correspondingly downwards on deflation. Repetition of the tests to evaluate repeatability and consistency established that the oscilloscope frequency peak enabled tyre pressure determination to within 2 or 3 psi. As shown in Fig 2, a test programme was carried out on 28 tyres of differing sizes and manufacturing origin and shows results which are largely linear and fall within a 20 hertz corridor. In Fig 3 tyres from just one tyre manufacturer were tested. The less linear plots relate to particular tyre types which incorporate a silicone additive to reduce rolling resistance. The results shown in Fig 4 indicate a fairly uniformly linear relationship between frequency and pressure, these relating to tyres from another single tyre manufacturer, as indicated. The method 10 of Fig 1 is embodied in commercial practice by means of the energy input device 12 (in a suitable practical format such as a constant height/ angle hammer adapted to apply a controllable or generally constant level of energy input to the tyre or wheel/rim assembly. For example, a power-operated impact device may be provided such as a solenoid- operated hammer adapted to generate continuously- repeated hammer strokes (such as are used in a bell- sounding mechanism) which can be readily mounted in relation to a vehicle wheel or rim or tyre, for example by magnetic or adhesive means. A battery or cable power supply mechanism is provided for the solenoid device. Other mechanical equivalents and related mechanisms are readily devised by the person skilled in the art. The length of piezo-cable 20 is provided with mechanical or adhesive means for attachment to the wheel and/or rim and/or tyre and likewise is connected to the voltage analysis means 22. This latter equipment may comprise a PC-based software system employing algorithmic analysis for identification of the frequency and/or time domain shifts of the dominant peaks in the emf output of piezo-electric cable 20. In use, the application of repeated impacts at a generally constant energy level and generally constant intervals enables the dominant peaks to be readily monitored, and this can then be easily done during the tyre inflation process in order to monitor the rising pressure. The person skilled in the art is well able to design modifications and supplemental technical features for the system described above on the basis of the above-identified requirement to identify dominant peaks in a system calibrated in terms of numerical tyre pressure against frequency and/or time domain shifts.

Claims: CLAIMS : 1 A method of tyre pressure determination comprising : a) subjecting a tyre to energy input; by an impact device providing mechanical impact with a tyre or with its associated wheel and/or rim; b) generating a corresponding energy waveform output from said tyre by means of electrical transducer means; c) analysing said waveform output to determine tyre pressure by reference to the waveform generated by said transducer; characterised by d) employing as said electrical transducer a length of piezo-electric cable. 2 A method of tyre pressure determination characterised by subjecting a tyre to vibrational or acoustic input and using a piezo-electric cable to generate a corresponding waveform from the tyre and analysing same to determine tyre pressure. 3 A method according to claim 1 or claim 2 characterised by performing said analysis by reference to the dominant peak of said waveform produced by said piezo-cable. 4 A method according to any one of the preceding claims characterised by effecting said mechanical impact by means of a falling or driven article such as a hammer adapted to cause repeated impacts with said tyre and/or rim and wheel. 5 Apparatus according to claim 4 characterised by means to cause said mechanical impact to have a controllable or generally constant level of energy input to said tyre or wheel and/or rim. 6 A method . according to any one of claims 1 to 5 characterised by effecting said analysis step by reference to a time-base shift of waveform data from said tyre, with pressure changes. 7 A method according to any one of claims 1 to 5 characterised by effecting said analysis step by reference to a frequency-based shift of waveform data from said tyre, with pressure changes. 8 Apparatus for tyre pressure determination comprising : a) energy input means adapted to subject a tyre to energy input and comprising an impact device adapted to cause mechanical impact with a tyre or with its associated wheel and/or rim; b) waveform generation means comprising an electrical transducer adapted to generate a corresponding electrical waveform output from energy input to said tyre; c) analysis means adapted to determine tyre pressure by analysis of said energy waveform output; characterised by d) employing as said electrical transducer a piezo- electric cable. 9 Apparatus for tyre pressure determination comprising tyre energy input means adapted to effect vibrational acoustic energy input, energy waveform generation means to generate a waveform from said energy input to a tyre, and analysis means adapted to analyse a waveform generated by said waveform generation means, characterised in that said waveform generation means comprises a length of piezo-electric cable. 10 Apparatus according to claim 8 or claim 9 characterised by said analysis means being adapted to analyse said waveform by reference to a dominant peak. 11 Apparatus according to any one of claims 8 to 10 characterised by said energy input means being adapted to provide a controllable or generally constant energy input by controlling the energy input to said impact device. 12 Apparatus according to any one of claims 8 to 11 characterised by said energy input means comprising a device adapted to cause an article to fall or to be driven to effect repeated impacts with said tyre and/or wheel/rim assembly. 13 Apparatus according to any one of claims 8 to 12 characterised by said analysis means being adapted to effect said analysis by reference to a time base shift of data obtained from said tyre, with respect to pressure. 14 Apparatus according to any one of claims 8 to 12 characterised by said analysis means being adapted to effect said analysis by reference to a frequency-based shift of data obtained from said tyre, with respect to pressure. 15 Apparatus according to any one of claims 8 to 14 characterised by said piezo-electric cable being adapted to be mounted in contact with said tyre and/or its wheel/rim assembly.

Inventors: CLIFTON JASON MARK, JONES BARBARA LYNN, SMITH PAUL, STOLLERY DAVID, CLIFTON, JASON, MARK, JONES, BARBARA, LYNN, SMITH, PAUL, STOLLERY, DAVID
Applicants: CLIFTON JASON MARK, JONES BARBARA LYNN, SMITH PAUL, STOLLERY DAVID, SUN ELECTRIC UK LTD, CLIFTON, JASON, MARK, JONES, BARBARA, LYNN, SMITH, PAUL, STOLLERY, DAVID, SUN ELECTRIC UK LIMITED
Application year: 1998
Main classification: G01L17
IPC codes: B60C23, G01L17, G01M17