Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Reexamination Certificate
2000-01-13
2002-02-05
Raevis, Robert (Department: 2856)
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
Reexamination Certificate
active
06343506
ABSTRACT:
This invention relates to a method and apparatus for tire pressure determination particularly, but not exclusively, applicable to automotive vehicle tire pressure determination, notably as applied to automobile and truck tire pressure determination, but applicable to vehicle tire pressures generally.
Tire pressure surveys and other available data indicate a considerable need for some more convenient and readily used method for tire pressure determination than the conventional method of directly measuring the pneumatic pressure in the tire at the time of inflation and subsequently.
If some external sensor system could be provided which did not require any active intervention on the part of the vehicle driver, this would obviously be extremely beneficial and useful. However, although systems for remote sensing of vehicle operating parameters have been proposed including the use of ultrasonic sensors, no system of that kind appears to be readily applicable to tire pressure determination on a remote basis.
Nethertheless, we are aware from our co-pending European patent application EP 96307897.7 (our reference P52835EP), due to be published May 28, 1997, that sensory determinations through the tires of a vehicle can be effectively made using piezo electric sensors, notably such in cable and similar format whereby the loading of the cable is effected in such a manner that the load is applied at spaced apart positions on the piezo electric material.
We are aware of course that piezo electric cable type materials have been used widely for sensing traffic movements, with the piezo electric material in the format of a road-surface-mounted device which produces an electrical impulse on the passage of a vehicle. Such impulses may have been analysed in various ways in the past, mainly simply on the basis of mere counting of pulses. Possibly proposals may have been made for more sophisticated analysis of such data.
The present invention is based upon our discovery that the passage of a vehicle tire over a piezo electric cable produces a waveform which has characteristics of shape and form which enable the pressure of the tire to be determined by appropriate analysis of such form and/or shape. It is believed that it has not previously been proposed to analyse the waveform and/or shape of such piezo-electric-cable-produced electronic pulses for this purpose.
Moreover, we have discovered that the pulses thus produced are affected in terms of their pulse width and height by the speed of the vehicle and its weight. An important aspect of the present invention relates to the interpretation of the data obtainable from the piezo electric device to take account of these factors, including a method for actually eliminating or offsetting their effects.
The present invention takes as the state of the art from which claim 1 commences as the use of signals from piezo electric cable devices mounted on roadway surfaces for numerical traffic monitoring purposes.
DISCLOSURE OF PRIOR ART
There is disclosure in:
EP-A-0 545 641 (Exxon)
EP-A-0 656 269 (Exxon)
of a system for determining pneumatic tire pressure and/or velocity in which an two-dimensional array of force sensors in a driveway or the like determine the pattern of force distribution exerted by a tire in its contact footprint across the width of the tire and a computer determines tire pressure and/or velocity from the sensed contact forces.
There is disclosed in U.S. Pat. No. 4,630,470 (Brooke) a system for determining tire pressure of vehicles as they pass an instrumented check point on a roadway. Rigid corrugations on the roadway set the tires into vibration with a waveform which is a function of tire pressure. Below the roadway surface directly beneath a metal plate on which the corrugations are formed to provide the road surface there are provided multiple costly transducers which convert the mechanical vibrations caused by the tires to identical electrical waveforms. The spacing
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between adjacent ridges of the corrugations or ribs varies with the type of vehicle being checked. It has been found that the ideal spacing for a jeep is 2.0 inches and 3.1 inches for a 5 tonne military truck. In accordance with the invention, the spacing between the ridges 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 which has a differing spectrum from the others and therefore is at a different pressure. No means is disclosed for actual quantitative numerical determination of the tire pressure, but only for detecting differences in pressure.
To the best of the Applicants' knowledge there has been no prior proposal for the use of a piezoelectric cable sensor/detector device located on a roadway traversed by automotive vehicles to provide a signal which is generated by direct loading of the device by the compressive engagement by the vehicle tires across the lateral widths of the tires without any mechanical intervention or intermediary device (such as the ribs of the Brook patent), and from which signal the tire pressure is determined quantitatively directly by non-spectral analysis and without the need for comparison with detectors responding to other tires of the same vehicle.
There is disclosed in EP-A-0 387 092 (Gebert) traffic monitoring equipment such as traffic speed detection equipment. The invention is concerned with the provision of validation checks for such equipment to enhance the reliability and accuracy and convenience of operating such equipment. Such validation is needed, for example, in order to check the level of insulation resistance between conductors in a particular cable. The invention is applicable to any traffic data collection equipment. The idea is to monitor the gradual or abrupt deterioration of a cable in service conditions leading to degrading of the insulation resistance which can lead to erroneous measurements and degraded accuracy or reliability. The invention provides apparatus for validation checks applied to traffic monitoring equipment. For example, the invention checks the level of insulation resistance of the equipment (page 2, line 43). It also validates operation by means of a facility for signal strength monitoring (page 3, line 5). For this purpose, a minimal signal level is required as a valid trigger for time pulses and (line 12) “in reference to a curve of the signal drawn on a time base the first pulse (be it positive or negative), must have a minimum steepness ie a minimum value of the first differential of magnitude of the pulse with respect to time”. Claim 2 refers to the curve of the signal needing to have a minimum steepness for use for traffic speed detection purposes. Accordingly, the voltage profile has relevance only in relation to achieving a “minimal signal level before being detected as a valid trigger for time pulses” (see page 3 at line 7). The shape of the waveform is only used to determine whether the waveform is or is not acceptable in terms of meeting the prescribed requirement for a minimal signal. Having achieved that minimal signal level, the waveform is used merely as a pulse and speed is determined as stated on page 4 at line 32:—“in normal speed timing equipment using such cables two parallel spaced cables are set on the road in an array and the time is measured between a pulse being generated in a first cable and a pulse generated in the second cable by the same wheel set of a vehicle. On this basis speed is calculated by the formula distance divided by time”. This disclosure provides no suggestion that the skilled person could expect to determine numerically speed or any other vehicle parameter by means of waveform analysis.
There is disclosed in EP-A-0 502 803 (ECM) equipment for establishing efficient measurement of the dynamic loads applied to a roadway by traffic. It is stated that currently known signal processing methods do not take into account various factors including the effect of under-inflated tires and the object of the invention is to eliminate
Jones Barbara L.
Smith Paul
Stollery David
Raevis Robert
Seyfarth Shaw
Snap-on Equipment Limited
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