MXPA99010435A - Tyre pressure determination - Google Patents

Abstract

A method and apparatus for determining tyre pressure in automotive vehicles utilises twin spaced parallel and non-transverse piezoelectric cables which are traversed by a vehicle to produce a voltage pulse having a shapes or profiles characteristic of the tyre pressure. Waveform analysis on the basis of a software algorithm and/or look-up calibration data enables numerical pressure determination. The system is well adapted for remote automotive vehicle tyre pressure sensing under normal conditions of vehicle use.

Description

DETERMINATION OF PNEUMATIC PRESSURE This invention relates to a method and apparatus for determining tire pressure, particularly though not exclusively, applicable to the determination of tire pressure of automotive vehicles, notably as it is applied to the determination of tire pressure. of automobiles and trucks, but it is generally applied to vehicle tire pressures. Tire pressure investigations and other available data indicate a considerable need for some more convenient and easily employed method for tire pressure determination than the conventional method of directly measuring the tire pressure at the time of inflation and subsequently. If an external detector system could be provided that does not require any active intervention on the part of the driver of the vehicle, this would obviously be extremely beneficial and useful. However, although systems have been proposed for remote detection of vehicle operating parameters, including the use of ultrasonic detectors, no such system seems to be readily applicable to the determination of tire pressure on a remote base. However, we are aware of our co-pending European patent application EP 96307897.7 (our reference P52835EP), to be published on May 28, 1997, that detection determinations can effectively be made through the tires of a vehicle using piezoelectric detectors, notably such as in cable form and the like, whereby the loading of the cable is carried out in such a way that the load is applied in spaced positions in the piezoelectric material. We are aware of course that the piezoelectric cable type materials, have been widely used to detect traffic movements, with the piezoelectric material in the format of a road surface mounted device that produces an electrical impulse when passing a vehicle . These impulses may have been analyzed in various ways in the past, primarily in a simple way based on the simple counting of pulses. Proposals for more sophisticated analysis of these data may also have been made. The present invention is based on our discovery that when a vehicle tire passes over a piezoelectric cable, it produces a waveform having shape and structure characteristics that allow the tire pressure to be determined by proper analysis in this way and / or structure. It is considered that it has not been previously proposed to analyze the waveform and / or structure of these electronic pulses produced by piezoelectric cable for this purpose. Furthermore, we have discovered that the pulses thus produced are affected in terms of their width and pulse height, by the speed of the vehicle and its weight. An important aspect of the present invention relates to the interpretation of the data obtained from the piezoelectric device, to take these factors into account, including a method to eliminate or displace their effects at present. The present invention takes as the state of the art from which claim 1 begins as the use of signals from piezoelectric cable devices mounted on road surfaces, for numerical purposes of traffic verification. DESCRIPTION OF THE PREVIOUS TECHNIQUE It is described in EP-A-0 545 641 (Exxon) EP-A-0 656 269 (Exxon) a system for determining pressure and / or tire speed wherein a two-dimensional structure of detectors of force in a road or the like determine the pattern of distribution of forces exerted by a tire on its contact footprint across the width of the tire and a computer determines the pressure and / or speed of the tire from the contact forces detected. It is described in the patent of the U.S.A. No. 4,630,470 (Brooke) a system for determining tire pressure of vehicles as they pass an instrumented checkpoint on a road. Rigid corrugations on the road put the tires in vibration, with a waveform that is a function of tire pressure. Below the surface of the road directly underlying a metal plate in which the corrugations are formed to provide the road or road surface are supplied with multiple costly transducers «which convert the mechanical vibrations caused by the tires into shapes of electric wave identical. The spacing 26 between adjacent ridges of the corrugations or ribs varies with the type of vehicle verified. It has been found that the ideal spacing for a jip (jeep) is 5.08 cm (2.0 inches) and 7.87 cm (3.1 inches) for a military truck with a capacity of 5 tons. According to the invention, the spacing between the flanges is variable within this range. The waveforms produced by the tires passing over these ribs are subjected to spectral analysis based on the concept of detecting one or more tires that have a different spectrum from the others and therefore are at different pressure. Means for quantitative current numerical determination of the tire pressure are not described, although only to detect differences in pressure. To the best of the knowledge of the applicant, there has been no previous proposal for the use of a piezo electric sensor / sensor device located on a road traveled by automotive vehicles, to provide a signal that is generated by direct charging of the device, by coupling of compression by the tires of the vehicle, through lateral widths of the tires, without any mechanical intervention or intermediate device (such as the ribs of the Brook patent) and from this signal the tire pressure is quantitatively determined directly by non-spectral analysis and without the need for comparison with detectors that respond to other tires of the same vehicle. According to the invention, a method and apparatus for related tire pressure determinations are provided, as defined in the appended claims. In a mode described below, a method and apparatus are provided, with which the determination of tire pressure is effected by the simple fact of causing a tire structure / vehicle wheel to pass over a piezoelectric cable sensing element. elongated, for compression coupling with it across the lateral width of the tire, the detector is located on or on the road surface or similar. This can be done at a relatively low speed, for example during maneuvers within an automotive service facility or in a parking lot or gas station yard. As the tire of the vehicle in question passes over the cable to compress and load the same across the entire lateral width of the tire (i.e. the entire surface area of the tire in the relevant portion of its circumference), the cable produces a electromotive force comprising waveform voltage elements that go to positive and negative, as illustrated in Figures 4 to 6 of the accompanying drawings. We have discovered that these waveforms have characteristic shaped components that allow the pressure determination to be made based on the reference calibrated to previously obtained data. The shape of the voltage profiles that are obtained depends on the pressure of the tire and therefore the latter can be easily determined in a search reference base. In the modalities, it takes into account (by means of a software algorithm) the influence of the weight and speed of the vehicle (although in general they are low) in order to isolate as much as possible the available data that provide a direct measure of Tire pressure. The weight of the vehicle has a direct relationship with the amplitude of the voltage pulse produced, due to the fact that the voltage produced by a piezoelectric device has a direct relationship with the mechanical load applied to the device. According to this the weight component of the waveform produced by the device, it is processed based on calibration data that relate the weight of the vehicle to the voltage produced, so that in a given test, the output can be normalized by reference to a predetermined and uniform vehicle weight. Regarding the effect of the speed of the vehicle, a direct approach to eliminate this effect is available by simply repeating a certain test with the vehicle passing successively on detector elements spaced to a known separation, whereby the speed component of the data can be calculated and eliminated or reduced easily by an adjustment process. Therefore, with respect to eliminating or reducing the effect of the speed of the vehicle on the waveform, the following details of the approach can be adopted in a simple and cost effective manner, i.e. adopting the use of piezo wire detector elements. electric twins or in pairs, at a known spacing and position, so that the tire in question passes over each of them successively. In this way, twin voltage peaks are generated corresponding to time intervals corresponding to the speed of the vehicle. By a simple calculation technique, the speed of the vehicle can be determined and the effect of the exact speed of the vehicle can be deduced or displaced by reference to known data relating to the speed of the vehicle. In this way, a voltage profile or waveform is obtained for analysis, which, as far as it can reasonably be achieved, is free of the effect of the vehicle speed. A corresponding adjustment can be made as described above with respect to the weight of the vehicle. By arranging the piezoelectric cables to extend non-transverse with respect to the direction of travel of the vehicle, it can be arranged that the individual vehicle structures or axes on opposite sides of the vehicle produce corresponding individual signals which can be very easily related to the corresponding tires. , in such a way that remedial pressure adjustment steps can be taken easily and correspondingly.

In the described embodiment, the elongated piezo cables are mounted on the road surface in order to project at least a small distance over the surface, while they are located partially within corresponding channels or grooves formed in the road surface. Beneath each of the piezoelectric detectors is a baseplate that serves as a stable reference surface to support the sensor while being charged in use. On each sensor is a flexible protective cover that extends along the sensor, in order to allow it to be loaded by the wheels of the vehicle, while it is resistant to wear and surface abrasion and impact damage with the vehicle's tires. For example, the protective cover may be convex in format and formed from a flexible polymeric material such as natural or synthetic rubber with or without suitable fillers and / or embedded reinforcement materials. Likewise, various plastic sheet materials and sheet metal materials will have the necessary characteristics of wear and flexibility. Considerable variation in the details of assembling the piezo electric cables can be provided from the simplicity of just placing a cable (lined or otherwise protected) on a hard surface in the trajectory of the vehicles, through a variation of this in where the cables 26 and 28 in Figure 2 are simply supported on the road surfaces instead of the grooves, through a deeper grooved structure, where the cables are primarily below a road surface but have a flexible material on them in the groove and projecting from the slot for coupling with the tires of the vehicle. We are aware that proposals for the interpretation of data obtained from vehicle sensors mounted on the road may have been made by reference to the gradient of the voltage profile at some particular supposedly symmetric position and the present application does not involve this approach, which is considered a somewhat subjective basis for analysis compared to the approach adopted by the present invention, ie the determination of pressure by reference to the shape and total profile of the voltage pulses produced. Attention is also directed to the fact that the embodiments of the present invention produce their corresponding analysable waveform pulses by direct loading or compression of the elongated piezoelectric cable through the lateral widths of the vehicle tires, as they travel through them. The tires themselves exert directly on the simple cable sensor (but of course through one or more protective layers so that the sensor is not damaged or wears unacceptably for each step of the vehicle) a load that varies according to the pressure of the tire in determinable quantitative form. There is no need to cause the tire to drive a corrugated vibration generating plate with multiple transducers, producing a signal that requires spectral analysis as in the Brooke reference, nor is there a need to analyze the pattern of contact forces detected in the tire tread. as in the Exxon references. Modes of the invention will now be described by way of example with reference to the accompanying drawings showing the apparatus and corresponding voltage waveform data, which are obtained from the apparatus according to the invention, the waveform data illustrate the difference in shape and waveform profiles produced at tire pressures below and at and above the recommended pressures. In the accompanying drawings: Figure 1 shows a diagram illustrating the relations of position between a pair of elongated parallel piezo electric cables, connected to a data display and processing system and a corresponding automotive vehicle which runs in the direction indicated by the arrow and about to go through the detector elements; Figure 2 shows a sectional view and side elevation in the direction of observation indicated by the arrows II-II in Figure 2 and shows a vehicle wheel that is about to traverse the spaced piezo cables. Figure 3 shows a flow diagram representing the main elements of the data processing operation involved in the analysis of voltage pulses derived from piezoelectric cables; Figure 4 shows the pulse profile for a front advance tire at 1.05 kg / cm2 (15 psi) which corresponds to sub-inflation of the tire; and Figure 5 shows a corresponding pulse profile for a forward advancing tire at 1.97 kg / cm2 (28 psi) which corresponds to correct inflation of the tire; and Figure 6 shows the corresponding waveform profile for an excessively inflated tire at 3.16 kg / cm2 (45 psi). As illustrated in Figures 1 and 2, the apparatus to analyze data produced by a piezoelectric cable device 12 on a road or road 14, traversed by the automotive vehicle 16 and adapted to allow a determination of the inflation pressure of one or more tires 18, 20 to be made. , 22, 24 of the vehicle, comprises the following main elements. First, the piezoelectric device 12 comprises a pair of piezoelectric cables 26, 28 for compression engagement by the tires 18 through 24 across all the lateral widths of the tires, in order to generate a signal or pulse or voltage 30 (see Figure 3). The signal analyzing means 32 is provided to determine information regarding the tires 18 to 24 of the vehicle 16. As illustrated in Figure 1, the cables 26, 28 are arranged in parallel relation to each other, and not transversely with respect to the normal forward movement direction D of the vehicle 16. The cables are connected to the display and signal analyzing means 32 to apply voltage pulses 30. Figure 2 shows the tire 18 of the vehicle 16 approaching the sensors on the path 14 in the D direction and about to create a voltage pulse 30 on the sensor 26 for transmission to the display and signal analysis means 32. The piezoelectric cables 26, 28 are mounted on the surface of the road 14 so as to project partially on the surface of the road, while they are located within corresponding channels or slots formed on the road surface. Below each of the cables is a base plate 27, 29 which serves as a stable reference surface for supporting the cable while being loaded in use. Over each cable is a flexible protective cover 31, 33 extending longitudinally of the cable to allow it to be loaded by the individual wheels of the vehicle, while resisting surface wear and abrasion and impact damage with the vehicle's tires 18. Turning now to the signal display and analysis means 32, the main features of this data processing system are illustrated in Figure 3 as a flow chart, wherein the voltage pulse 30 is connected at 34 by the analog converter-a -digital (not shown) to a data processing system 36 wherein the voltage pulses 30 are processed in a manner analogous to that of the data processing system described in our co-pending application No. EP96305506.6 published on 29 / 01/97 (our reference P52740EP). Here we incorporate in the present application all the description of our previous application mentioned above, which is published as EP 0 756 167. According to the principles described therein, the software system of the data processor 36 comprises a software algorithm 38 for interpretation of the waveforms (see Figures 4 to 9) according to a data storage 40 of voltage profiles corresponding to known tire pressures, whereby the signal waveforms 30 of the detectors 26, 28 are They recognize in terms of their characteristic profiles, which can be identified on a search basis, which represent specific points on the progressive pattern of waveforms or voltage profiles that progressively change with tire pressure, whereby corresponding tire pressures can be easily identified and exhibited quantitatively (in numerical form) at 42. Alternately or In a supplementary manner, an algorithmic analysis may be provided to perform a corresponding quantitative pressure determination. In the examples shown in Figures 4 to 9, the waveforms of the voltage pulses produced are illustrated using an oscillocoscope storage connected to a single piece of 20-gauge piezo electric cable, placed on the floor of the waist at an angle lower than 90 ° with respect to the travel direction D of the vehicle 16. In these simple tests, the vehicle was advanced such that a tire 18 passed forward on the first cable 26, to produce the voltage pulses shown in the Figures 4 to 6 of the accompanying drawings.

The test procedure is carried out with the vehicle tire at three different pressures of 1.05, 1.97 and 3.16 kg / cm2 (15, 28 and 45 pounds per square inch), thus producing the voltage pulse profiles shown . In each case, the vehicle was advanced forward on the cable. The results in Figures 4 to 6 show that there is a progressive difference in shape or profile of the voltage waveform of the voltage pulse due to differences in tire pressure. By means of a graduated series of tests producing a corresponding graduated sequence of voltage profiles, it is possible to construct the data storage 40, allowing positive identification of specific tire pressures from the corresponding voltage pulse profiles, so that the pressure is easily determined in an algorithmic and / or search basis. By mutually parallel detectors 26, 28 in Figure 1, with each one providing its own voltage pulse for each of the four wheels of the vehicle 16 in Figure 1, two tire pressure readings can be easily obtained for each wheel. The effect of vehicle weight and speed on waveform profiles and amplitudes can be easily displaced by calibration data relating to them. The known spacing between the detectors 26, 28 allows the speed of the vehicle to be easily calculated and thus displaced by algorithmic analysis or look-up table data. Equally, a corresponding displacement for the weight of the vehicle can easily be obtained by any additional means of detecting weight on the road surface or by a simple vehicle categorization for the weight system. In one modification, two or more piezoelectric cables are arranged in spaced apart and generally parallel relationship in order to provide numbers of signals or pulses according to the number of tires (on associated shafts) that couple the cables to each side of the vehicle. In this way, the apparatus can determine the corresponding associated axle and tire numbers to estimate its pressure on each side of the vehicle.

Claims (17)

1. CLAIMS 1. A method to analyze data produced by a piezoelectric device located on a road traveled by automotive vehicles, comprising: a) locating a section of piezoelectric cable on or on a road surface or similar for compression coupling by a tire of an automotive vehicle through the lateral width of the tire; b) causing the vehicle to pass over the cable, in such a way that it compresses and loads it through the lateral width of the tire and thus generates a signal; c) analyze the signal to determine information regarding the vehicle; characterized by d) step of analyzing the signal comprises analysis of the shape or profile of the waveform produced by the compressive load of the piezoelectric cable, to determine in an algorithmic and / or search basis, the tire pressure.
2. 2. A method to analyze data produced by a piezoelectric detector located on a road or similar route by automotive vehicles, comprising: a) locating a piezoelectric detector for coupling with a tire of an automotive vehicle; b) cause the vehicle to pass over the detector and generate a signal; c) analyze the signal to determine information regarding the vehicle; characterized by: d) the step of locating the piezoelectric detector for coupling by a tire of an automotive vehicle comprises using as the detector a piezoelectric sensor element adapted to be subjected to localized charging.
3. 3. A method for analyzing data produced by a piezoelectric device located on a road traveled by automotive vehicles, which comprises: a) locating a piezoelectric detector for coupling with a tire of an automotive vehicle; b) cause the vehicle to pass over the detector and generate a signal; c) analyze the signal to determine information regarding the vehicle; characterized by: d) the step of analyzing the signal to determine information relating to the vehicle, comprising analyzing the waveform of the signal to eliminate or reduce the effect of the weight and / or speed of the vehicle in the waveform.
4. 4. A method according to claim 1, characterized in that the step of analyzing the signal to determine the information comprises using an algorithm to analyze the waveform based on progressive changes in the waveform with respect to progressive changes in pressure of tire.
5. 5. A method according to claim 2, characterized in that the piezoelectric detector is adapted for localized charging by the piezoelectric detector element that is in the form of an elongated rope or rope-like element in such a way that the load is applied mechanically only to a portion of its external profile.
6. 6. A method according to claim 3, characterized in that the analysis to eliminate or reduce the effect of the weight of the vehicle comprises adjusting the waveform amplitude according to the calibration data relating to the weight of the vehicle.
7. A method according to claim 3, characterized in that the step of analyzing the waveform to eliminate or reduce the effect of the speed of the vehicle in the waveform comprises performing an adjustment step in relation to data obtained from the detector electric piezo, so that the tire passes sequentially on detectors spaced first one and then the other.
8. A method according to any of the preceding claims, characterized in that it comprises locating the piezoelectric detector in the form of an elongated detector disposed in a non-transverse manner with respect to the intended direction of the normal travel vehicle, so that the wheels on opposite sides of a vehicle couple the detector in a non-simultaneous manner and in this way produce sequential signals that can be analyzed individually.
9. 9. Apparatus for analyzing data produced by a piezoelectric detector located on or on a road or similar surface covered by automotive vehicles or the like, the apparatus comprises: a) mounting by a section of the piezoelectric cable adapted to mount the same for compression coupling by tire of automotive vehicles, in such a way that the tires can pass over the detector in order to compress and load the same to through the alteral width of the tires, in order to generate a signal; b) means of signal analysis to determine information relating to the vehicle; characterized by c) the analysis means are adapted to analyze the shape or profile of the waveform produced by compressive loading of the piezoelectric cable to determine in an algorithmic and / or search basis, the tire pressure.
10. 10. Apparatus for analyzing data produced by a piezoelectric detector located on a road traveled by automotive vehicles and the like, the apparatus comprises: a) a piezoelectric detector and a mounting for the same adapted to mount it for coupling by vehicle tires automotive, so that the tires can pass over the detector to generate a signal; b) means of signal analysis to determine information relating to the vehicle; characterized by: c) the piezoelectric detector comprises an electric piezo element adapted to be subjected to localized load when mounted in this way by the assembly.
11. 11. Apparatus for analyzing data produced by a piezoelectric detector located on a road traveled by automotive vehicles and the like, the apparatus comprises: a) mounting a piezoelectric detector adapted to place the same in coupling by automotive vehicle tire, in such a way that the tires can pass over the detector to generate a signal; b) means of signal analysis to determine information relating to the vehicle; characterized by: c) the analysis means are adapted to analyze the waveform of the signal, reduce or eliminate the effect of the weight of the vehicle and / or speed of the vehicle in the waveform.
12. 12. Apparatus in accordance with the claim 9, characterized in that the analysis means are adapted to employ an algorithm to analyze the waveform based on progressive waveform changes with respect to the pressure.
13. 13. Apparatus in accordance with the claim 10, characterized in that the detector is adapted for localized loading by being in the form of an elongated element of rope or cable or filament-like shape, such that the load is applied mechanically only to a portion of its external profile.
14. Apparatus according to claim 11, characterized in that the step of providing two spaced piezoelectric detectors located in a path for sequential travel by automotive vehicles and the step of analyzing the signal to determine information regarding the vehicle comprises obtaining the signals successively produced by the tire, a measure of vehicle speed and adjust the waveform according to the speed based on known data.
15. 15. Apparatus according to claim 11, characterized by providing a pair of piezoelectric detector cables spaced apart to make runs in sequence by the automotive vehicle, and the analysis means are adapted to determine a measure of the vehicle speed and adjust the Waveform or profile for analysis according to the speed of the vehicle.
16. 16. Apparatus according to any of claims 9 to 14, characterized in that the piezoelectric detector cables comprise an elongate sensing element, adapted to be placed in a non-transverse manner with respect to the intended direction of vehicle travel in forward normal forward motion, when they are coupled in order that "the wheels on opposite sides of the vehicle will couple the detector in a non-simultaneous manner and in this way produce sequential signals that can be analyzed individually. Apparatus according to claim 16, characterized in that at least two of the piezoelectric cables are arranged in a generally parallel relationship in order to provide signal numbers, according to the number of tires (on associated axes) that couple the cables on each side of a vehicle, whereby the apparatus can determine the numbers of corresponding axes and associated tires to estimate the pressure on each side of the vehicle.