Tire pressure monitoring system with a computer on a wheel of the vehicle
The invention relates to tire pressure monitoring systems of motor vehicles and more specifically to such systems when able to automatically locate the tire with insufficient pressure. In a tire pressure monitoring system, each tire is equipped with a pressure sensor and a radiofrequency transmitter, which emits tire pressure data, ie either a pressure value or a pressure indication. insufficient. The transmitter also transmits an identifier code which makes it possible to discriminate it from the transmitters of the other tires. Therefore it would be sufficient, in principle, to match each transmitter code with a location data stored centrally in the vehicle, this step being done on the assembly line, in order to be able to indicate to the dashboard which tire is faulty. This does not take into account the various changes of tires, interversions, equipment and equipment in snow tires, etc. ... intervening during the life of the vehicle. Also it is desirable to equip the vehicles means achieving an automatic location of the tire sending a given pressure signal. In this approach, and assuming that the four wheels of a vehicle do not rotate at the same speed for different reasons (different turns, inflation, ground conditions, etc.), and based on the principle that we have 'an exact speed of rotation of a wheel well identified thanks to ABS - anti-lock wheel system - or ESP - trajectory correction system - it was proposed to take advantage of periodic variations in the magnitude of the signal received from pressure sensors, to date these periodic readings during the period and derive a value of wheel speed by means other than the ABS system, this time in association with the code of each tire transmitter. It is then sufficient to correlate the wheel speeds obtained by the ABS or ESP sensors with the wheel speeds obtained by means of the pressure sensor signals to associate a wheel identifier with a wheel location. This principle, which is based on the analysis of the periods of the pressure signals, remains of a complexity of treatment such that it makes it not adaptable to certain vehicles. In addition, the signals transmitted by the transmitter of the valve will have to present a calibration such that they are legible and processable by the vehicle, resulting in compatibility problems between wheels / tires and vehicles, making this principle not robust to maintenance hazards of vehicles. The invention relates to a means for automatic tire location monitored by comparing speed ABS and speed derived from a parameter originating in the tire, which means is simpler to implement, a greater adaptability to various types of vehicles , low cost, and better location reliability than known systems. This object is achieved according to the invention by means of a system for monitoring the tire pressure of a motor vehicle, comprising a pressure sensor, on each wheel of the vehicle and a central pressure monitoring module (16), a radiofrequency signal transmitter on each wheel of the vehicle for transmitting a pressure indication and a wheel identifier to the central pressure monitoring module; a module for locating at least one wheel of the vehicle, the system further comprising a calculator); indicative value of the angular velocity of the wheel from a periodic signal delivered by a sensor on the wheel and an angular displacement sensor of the wheel so that the locating module performs a correlation between two values indicative of the angular velocity of wheels respectively obtained from the periodic signal delivered by the sensor on the wheel and at firing of the wheel angular displacement sensor, characterized in that the computer establishing a value indicative of the angular speed of the wheel from a periodic signal delivered by a sensor on board the wheel is a computer on board the vehicle wheel so that the value indicative of the angular velocity of the wheel established by this computer, is transmitted by the radiofrequency transmitter of the wheel to the locator module Other features, objects and advantages of the invention will appear on reading of the description which follows, with reference to the appended figures in which: - Figure 1 schematically shows a tire pressure monitoring system according to the invention - - Figure 2 illustrates in the form of a diagram a first mode embodiment of the invention in which a duration separating two threshold crossings is measured; FIG. 3 illustrates in the form of a iagram a second embodiment of the invention wherein there is a number of threshold crossings for a given duration. In a manner known per se and as shown in Figure 1, the system described here is based on the use of a set of four angular rotation sensors 11, 12, 13, 14 pre-existing in an antiblocking system of ABS wheels, and comparing a value indicative of wheel speed as obtained from each of the ABS sensors with other values to deduce the location of the wheels. As will be seen below, the wheel rotation ABS sensors 11, 12, 13, 14 and transmit to a centralized ABS computer 15 signals which may include a value indicative of the angular velocity, such as the value. the angular velocity itself in number of revolutions per second, a measure of the period of rotation of the wheel or the frequency of rotation of the wheel, or be a raw signal from which it will be necessary to make a dating, a calibration, or a filtering to obtain a value indicative of the wheel angular velocity, such as a simple pulse train whose each of the pulses corresponds to a wheel revolution. A wheel is currently considered as a set formed by the rim and the tire.
From the signal received from the different wheel rotation sensors 11, 12, 13, 14, the ABS computer 15 transmits four values of instantaneous angular wheel speed to a pressure monitoring module 16 also forming a wheel locator. The locator module 16 receives meanwhile other signals 21, 22, 23, 24 coming from four wheel transmitters 31, 32, 33, 34 equipped with means for measuring wheel parameters such as tire pressure in order to transmit these wheel parameters to the wheel monitoring and locating module 16. These wheel transmitters 31, 32, 33, 34 are placed on the rim or tire of a given wheel, and typically integrated with an electronic valve which , in addition to its inflation and maintenance of the latter, has an electronic equipment for measuring the pressure and transmitting the pressure value by radiofrequency. The monitoring module 16 implements a comparison of the measured pressure value with a minimum pressure level. It can also only display the pressure value read. In a variant, the monitoring module may consist only of a correctly correct or incorrect pressure binary signal display module, the binary signal being itself received as such from the wheel transmitter 31, 32, 33, 34 The monitoring and locating module 16 has for the reception effect of these radio frequency signals a reception antenna which can also be used for the reception of other types of signals such as a door opening control signal. of the vehicle. According to the embodiment described here, each of the emitters 31, 32, 33, 34 includes an accelerometer, known per se and usually used to know the direction of rotation of the wheel. This accelerometer delivers a periodic acceleration signal S, as shown in FIG. 1. The periodicity of this acceleration, whether it is measured tangentially or radially to the wheel, is essentially due to the presence of the gravity vector. Although a periodic acceleration signal is used here, other types of periodic signals can be obtained on the wheel, such as a pressure, displacement or deformation signal. The periodic signal, here a sinusoid, can also be a square signal or even a pulse train, each of which is obtained for example for a given angular position of the wheel. The periodicity of the periodic signal processed by the computer may be due to a periodicity of information such as generated by the sensor itself, as is the case for an acceleration measurement which is periodic by the very existence of Earth's gravity. This periodicity may also be due to a periodic deformation of the signal generated by the sensor, for example a deformation due to a lateral displacement of the sensor due to the deformation of the tire, or to a disturbance of the sensor output signal due to the proximity from the surface of the road to each wheel revolution. In addition, the periodic signal processed by the computer may alternatively include different periodic components, which may be periodic signals by the nature of the measurement and / or periodic signals by signal deformation. Each wheel is here equipped with a computer, preferably integrated with the transmitter 31, 32, 33, 34, and also in the valve of the wheel, which analyzes the periodic signal and delivers from the latter a numerical value indicative of the angular velocity of the wheel. The periodicity of the periodic signal processed by the computer may be due to a periodicity of information such as generated by the sensor itself, as is the case for an acceleration measurement which is periodic by the very existence of Earth's gravity. This periodicity can also be due to a periodic deformation of the signal generated by the sensor, for example a deformation due to a lateral displacement of the sensor due to the deformation of the tire, or to a disturbance of the sensor output signal due to the proximity from the surface of the road to each wheel revolution. In addition, the periodic signal processed by the computer may alternatively include different periodic components, which may be periodic signals by the nature of the measurement and / or periodic signals by signal deformation. In the present embodiment, the computer 31a, 32a, 33a, 34a contains in memory an accelerating threshold value Sa chosen to be crossed upwards by the periodic acceleration signal S at each wheel revolution. The computer 31a, 32a, 33a, 34a samples the periodic acceleration signal S at a sampling frequency f and stores the successive values thus sampled in dedicated memory zones. The calculator 31a, 32a, 33a, 34a then compares each sampled value with the threshold value Sa, and identifies the samples corresponding to a crossing of the threshold value Sa. Once two values S1 and S2 of the signal S corresponding to a crossing of the Sa threshold identified, the calculator counts the numbers of sampled values that separate the two values S1 and S2, and deduces a duration T corresponding to the time required for the wheel to turn a wheel. This duration T may constitute the value indicative of the angular velocity of the wheel as it is then transmitted to locator 16. In a variant, the wheel calculator may perform an inversion of T in order to deduce the frequency of rotation of the wheel, or to multiply this frequency by a constant for conversion into an angular value, or multiply this frequency by a metric value of circumference of the wheel to obtain a value of linear wheel speed in the road reference system. The indicative speed value is then transmitted by the radio frequency wheel transmitter to the locator 16. The locator 16 then compares each wheel speed indicative value as obtained from the transmitters 31, 32, 33, 34 with the indicative values of wheel speed as obtained by the wheel speed sensors 11, 12, 13, 14 of the ABS system in order to associate the wheel speeds corresponding to the same wheel within each of these sets of four values indicative of speed. For example, the locator will rank in each series the four speeds in ascending order and establish the pairs of speeds whose two speeds correspond to the same order in the series.
Of course, the present system can be implemented wheel by wheel, that is to say by comparison within the locator between two values indicative of speed of a given wheel and thus obtained by two different means, then by discrimination as to the correspondence or not of the two speeds. According to another embodiment shown in FIG. 3, the wheel calculator samples the signal S, and stores the sampled signal S during a period of time which is preset so that the signal S crosses the threshold Sa with a variable number of occurrences, preferably varying between 2 and 20, depending on whether the wheel is at a fast or slow speed, and making it possible, by obtaining this number of occurrences, to discriminate the different wheels for the same speed of the vehicle. In this embodiment, the observation time is for example 20 times the period of revolution of a wheel at medium speed of the vehicle.
The calculator then identifies the different threshold crossings S1, S2,... Sn appearing during the observation period and stores the number of these threshold crossings. The numerical value of this number of threshold crossings during the observation period is then communicated as it is to the locator 16 as a value indicative of the wheel angular velocity, the calculator having for this purpose also known the duration of the 'observation. As a variant, the local computer 31a, 32a, 33a, 34a performs additional processing on this number of threshold crossings in order to deliver another numerical value indicative of the speed such as the value of the angular speed itself of the wheel.
The threshold crossings described and detected here are threshold crossings on the rise, but the calculator can just as well be programmed to detect threshold crossings downward, upwards and downwards. An alternative is to count a number of crossings of several threshold values in order to obtain a number of occurrences of the crossings that is higher for a given observation period. The observation time can then be chosen shorter while allowing to effectively discriminate between the different wheels. The correlation between the indicative speed value of a wheel, obtained on one side by the ABS sensor and on the other hand by the onboard computer on the wheel, is then implemented in the same way as in the embodiment previous. Thus, the indicative speed values of the ABS system being correlated to a localized wheel ab initio, and the speed indicative values obtained by the on-board computers on the wheels being correlated with an ab initio pressure sensor, the correlation speeds allows to correlate a pressure sensor with a location.