Abstract:
The pressure of a vehicle tire fitted on a vehicle wheel is measured and regulated, utilizing a source of compressed air, a check valve leading to an interior of the tire, and an air feed circuit connecting the air source to the check valve. Compressed air is fed from the air source into the circuit and against the check valve to tend to open the check valve. A pressure drop is imposed at a point in the circuit, wherein a resulting pressure drop in the circuit downstream of such point and upstream of the check valve is less than 10% of the pressure drop at the point. A measurement is made of the pressure in the circuit at a location downstream of the point, or in the tire itself. The evolution of the pressure measured in step D is analyzed as a function of time, to determine whether the check valve has been opened.

Description:
The present application claims priority under 35 U.S.C. § 119 to French Application No. 05/00827 filed on Jan. 27, 2005. 
   BACKGROUND 
   The present invention concerns a device and process for measuring and regulating the pressure of at least one tire fitted on a vehicle wheel. 
   From the prior art, in particular from the document EP-B1-0 671 998, a device is already known for measuring and regulating the pressure of a tire fitted on a vehicle wheel, of the type comprising a source of compressed air, an air feed circuit that connects the said source to the tire, and pressure measurement means in the circuit or in the tire. 
   In the remainder of this description the circuit will be regarded as extending from the air source towards the tire. Thus, “upstream” refers to a part of the circuit which is closer to the air source and “downstream” to a part of the circuit closer to the tire. 
   The feed circuit generally comprises a check valve which opens when the pressure in the circuit exceeds the pressure in the tire by a predetermined value. 
   When the tire is fed with air by a device of the above type, the pressure in the circuit or in the tire is generally unstable. Inasmuch as the pressure is unstable, it is difficult to measure the pressure in the circuit or in the tire exactly. To avoid this problem it has therefore been proposed to measure the pressure of a tire by the following procedure:
         the circuit is fed with compressed air so as to open the check valve and place the circuit and the inside of the tire in fluid communication,   the compressed air feed is stopped,   stabilization of the pressure in the circuit and tire is awaited, and   the pressure in the circuit or tire is measured.       

   This process enables a precise measurement of the pressure in the tire to be obtained during its inflation, but entails frequent stopping of the compressed air feed. The process is therefore particularly lengthy and restrictive. 
   Moreover, with this tire pressure measurement process, each time the pressure in the circuit is measured some air is injected into the tire, and this increases its pressure. Thus, too many pressure measurements risk increasing the tire pressure abnormally. 
   The purpose of the invention is to overcome pressure instability problems so as to enable more precise regulation of the pressure in the tire. 
   SUMMARY OF INVENTION 
   To that end, the object of the invention is a device of the above type for measuring and regulating the pressure of at least one tire fitted on a vehicle wheel, characterized in that the circuit comprises means interposed in the circuit, which are designed to bring about a forced pressure drop, the pressure drop of the circuit downstream from the pressure drop production means being less than 10% of the pressure drop produced by the pressure drop production means, and in that the pressure measurement means measure the pressure, whether in the tire or in the circuit, downstream from the pressure drop production means. 
   In what follows, “downstream part” and “upstream part” will be used to designate respectively the parts of the circuit downstream and upstream from the pressure drop production means. 
   The pressure drop production means in the circuit enable the pressure of the air injected into the downstream part of the circuit by the air source to be reduced and made more uniform. Thus, pressure instability problems in the circuit are overcome and this, in particular, allows the pressure in the tire to be estimated by measuring the pressure in the circuit before the circuit and tire are placed in communication. It also enables reliable pressure measurements to be made during inflation, without any need to await pressure stabilization in the tire and in the circuit. 
   A pressure regulation device according to the invention can also have one or more of the following characteristics:
         The pressure drop in the circuit downstream from the pressure drop production means is between 3% and 6% of the pressure drop of the pressure drop production means. Tests have shown that these values enable a particularly stable pressure to be obtained in the circuit.   The pressure drop production means comprise a constriction. A localized reduction of the circuit cross-section in effect enables a sufficient pressure drop to be obtained.   The constriction comprises at least one nozzle.   The downstream part of the circuit comprises a check valve which opens when the pressure in the said downstream part of the circuit exceeds the pressure in the tire by a predetermined value, preferably close to zero. For example, a one-way valve is used which, during inflation, allows air to be injected into the tire in a simple way by bringing the circuit to a pressure higher than that in the tire. As soon as the tire pressure exceeds the pressure in the circuit, the one-way valve closes and this prevents the tire from deflating.   The downstream part of the circuit comprises a solenoid valve interposed upstream from the valve. The presence of solenoid valves enables the pressure of a tire to be regulated independently of the vehicle&#39;s other tires.   The device regulates the pressure of two tires, and comprises a solenoid valve common to the two air feed circuits of the two tires, the parts of the circuits downstream from the said solenoid valve being in fluid communication. This configuration of the pressure regulation device enables the pressure to be equilibrated between the two tires. This is particularly advantageous for ensuring that the two tires on the front or on the rear axle of the vehicle are inflated to an identical pressure.   The device is designed to regulate the pressure of two tires, each feed circuit comprising a solenoid valve, the said solenoid valve being arranged so as to allow fluid communication between the parts of the circuits located upstream from the solenoid valves. Thanks to this configuration it is possible to re-use the compressed air from the downstream part of the circuit of a tire that has just been inflated, to increase in advance the pressure in the downstream part of the circuit of another tire which it is desired to inflate.   The check valve is carried by the wheel.   The device comprises means for analyzing the evolution of the pressure measured by the pressure measurement means as a function of time. These analysis means can detect a variation of the pressure evolution due to the opening of the check valve. A measurement of the circuit pressure at the moment when the check valve opens enables the tire pressure to be estimated.   The circuit comprises several elements whose junctions with one another, with the air source or with the tire are designed to allow an air leak at a flow rate much smaller than the flow rate coming from the source. This property enables the circuit to return to atmospheric pressure after having been pressurized, but without this air leak disturbing the regulation of the tire pressure.   The pressure measurement means consist of a pressure sensor placed in fluid communication with the upstream branch of the feed circuit and downstream from the pressure drop production means.   The pressure measurement means consist of a pressure sensor in fluid communication with the internal cavity of the tire.       

   The device according to the invention can advantageously be associated with a device for measuring the pressure of a vehicle&#39;s tires, of the type comprising means for comparing the rotation speeds of at least two tires. 
   A tire pressure measurement device comprising means for comparing the rotation speeds of at least two tires is known from the prior art. This device uses the following property: when a tire loses pressure, it collapses under the effect of the vehicle&#39;s load, and this modifies its circumference. Consequently, for a given linear speed a less inflated tire has a rotation speed different from that of a correctly inflated tire. 
   By comparing the rotation speeds of the vehicle&#39;s tires, it therefore becomes possible to determine the relative pressures of the different tires. 
   However, when rounding a curve an external tire always rotates faster than an internal tire. Consequently, in certain conditions of the vehicle&#39;s use such as on winding mountain roads, the rotation speed differences of the tires are not due solely to differences of their pressures. In certain situations the comparison of tire rotation speeds is therefore not effective for determining the different tire pressures of the vehicle. It is thus advantageous to couple means for comparing the tire rotation speeds with a device for regulating the pressure of a tire as described earlier, so as to obtain a tire pressure measurement device that works regardless of the tire&#39;s conditions of use. 
   According to a particular embodiment, the device comprises means for estimating the pressure in a tire from comparison means and/or pressure measurement means. Thanks to this special form the pressure in the tire is estimated either from comparison means when the tire&#39;s conditions of use allow this, or from the pressure sensor in the downstream part of the circuit in the remaining cases. Since the comparison means are software means, they are simpler to use and consume less energy than the device for regulating the pressure in a tire according to the invention, while also enabling quasi-continuous monitoring. It is therefore advantageous to use the comparison means as often as possible to estimate the tire pressure. 
   Since the invention enables pressure instability problems in the air feed circuit or in the tire to be overcome, it is conceivable to measure or at least estimate the pressure in the tire as often as possible by implementing a process of type different from that described above, which in particular avoids the risk of abnormal tire inflation. 
   Thus, another object of the invention is a process for measuring and regulating the pressure of an automobile vehicle tire by means of a measurement and regulation device such as that defined earlier, in which the pressure measurement means measure the pressure in the circuit, characterized in that:
         the circuit is fed with compressed air,   the pressure in the circuit is measured,   the evolution of the pressure measured is analyzed as a function of time,   Thanks to the invention, monitoring the evolution of the measured pressure makes it possible to obtain a lower value estimate of the tire pressure based on measurement of the pressure in the circuit before it is placed in communication with the tire. Consequently, the tire pressure measurement does not necessarily introduce air into the tire.       

   A process for measuring and regulating the pressure according to the invention can also comprise one or more of the following characteristics:
         The evolution of the measured pressure is analyzed so as to detect an event chosen from between an event that characterizes the opening of the check valve, and an event showing that a given pressure threshold has been exceeded. These two events are particularly interesting for estimating the pressure inside the tire. In effect, the first event demonstrates that the pressure in the circuit is essentially equal to the pressure in the tire. The second event shows that the tire pressure is at least equal to the predetermined pressure.   When the first event detected is the opening of the check valve, the air feed to the circuit is maintained so as to inflate the tire. For the tire to be inflated, the check valve must first be open. Once the check valve is known to be open, i.e. when the first event is detected, the tire is inflated by maintaining the air feed.   When the first event detected is that the predetermined pressure threshold has been exceeded, the air feed to the circuit is stopped and the pressure in the tire is estimated as a function of the threshold. This enables a lower value estimate of the tire pressure to be obtained.   When the predetermined threshold is exceeded before the check valve is opened, the air feed to the circuit is stopped and the tire pressure is assimilated to the pressure indicated by the sensor. In certain situations it is desired to know the exact pressure in the tire even if that pressure is higher than a predetermined minimum threshold pressure. Then, the feed is stopped only when the opening of the check valve has been detected.   The process is intended for measuring and regulating the pressure in a first and a second tire by means of a regulation device as defined earlier, in which, after having measured or regulated the pressure in the first tire, the solenoid valve of the second tire&#39;s feed circuit is opened so that the pressure in the first tire&#39;s feed circuit is reduced abruptly, to close the check valve of the first tire&#39;s circuit. This stage is applicable in any variant of the device according to the invention.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood on reading the description presented below, which is given solely as an example and which refers to the attached drawings, showing: 
       FIG. 1 : Schematic illustration of a device for regulating the pressures of the tires of an automobile vehicle, according to a first embodiment of the invention 
       FIG. 2 : Schematic illustration of a second embodiment of a regulation device according to the invention 
       FIGS. 3 to 6 : Graphs representing the pressure evolution in the air feed circuit of the device illustrated in  FIG. 1 , as a function of time, in four different configurations, and 
       FIG. 7 : Schematic illustration of a pressure regulation device according to a third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a schematic representation of four tires of an automobile vehicle. These four tires are denoted by the general indices  10   a ,  10   b ,  10   c  and  410   d . The tires  10   a  and  10   b  are part of a front axle of the vehicle, as distinct from the tires  10   c  and  10   d  which are part of a rear axle of the vehicle. Each tire  10   a ,  10   b ,  10   c ,  10   d  is fitted on a vehicle wheel  12   a ,  12   b ,  12   c ,  12   d.    
   Each wheel  12   a ,  12   b ,  12   c ,  12   d  is connected to a sensor  14   a ,  14   b ,  14   c ,  14   d  that detects the rotation speed of the wheel. Such sensors  14   a ,  14   b ,  14   c ,  14   d  are classically used in wheel anti-blocking systems of the ABS (Anti-Blocking System) type. Each of the sensors  14   a ,  14   b ,  14   c ,  14   d  is connected to a vehicle computer  16  by means of electric cables  18 . 
   The measurements furnished by the sensors  14   a ,  14   b ,  14   c ,  14   d  are treated by wheel rotation speed comparison means  20  integrated in the computer  16 . 
   The computer  16  also comprises means  22  for estimating the pressure in the tires  10   a ,  10   b ,  10   c ,  10   d , capable of using data furnished by the tire rotation speed comparison means  20  for estimating the tire pressures. The estimate of tire pressures provided by the means  22  is correct in most cases, but it can happen, particularly on winding roads, that this pressure estimate is incorrect. 
   Consequently, the automobile vehicle comprises a device  19  for measuring and regulating the tire pressures, which besides the tire rotation speed comparison means  20 , also comprises a device  23  for measuring and regulating the pressure according to the invention connected to the pressure estimation means  22 . Thus, the means  22  estimate the tire pressures from the comparison means  20  and/or from pressure measurements furnished by the device  23 . 
   The tire pressure regulation device  23  comprises a source  24  of compressed air that can be controlled by the computer  16 . This air source  24  is for example a compressor or a bottle of compressed air, whose means of operation or of being connected in communication are not shown. 
   The air source  24  is connected to the four tires  10   a ,  10   b    10   c ,  10   d  by a feed circuit  25 . According to a first embodiment, the feed circuit  25  comprises an upstream branch  26  connected to four downstream branches  27   a ,  27   b ,  27   c ,  27   d . The upstream branch  26  is connected to the air source  24  and each downstream branch  27   a ,  27   b ,  27   c ,  27   d  is connected to a tire by means of a bearing  28   a ,  28   b ,  28   c ,  28   d  with an air passage and a check valve  30   a ,  30   b ,  30   c ,  30   d . Note that in  FIG. 1  the four bearings illustrated correspond to bearings for drive axles. 
   The check valves  30   a ,  30   b ,  30   c ,  30   d  are classical one-way valves which open when the pressure in the downstream branch  27   a ,  27   b ,  27   c ,  27   d  exceeds the pressure in the tire  10   a ,  10   b ,  10   c ,  10   d  by a predetermined value, preferably close to zero. Generally, the predetermined value is small and of the order of 10 millibars for a valve of good quality. Since this value is virtually constant throughout the life of the valve, it is easily modelled and taken into account when measuring the pressure in the tire. 
   A solenoid valve  32   a ,  32   b ,  32   c ,  32   d  is interposed in each downstream branch  27   a ,  27   b ,  27   c ,  27   d  between the tire and the air source  24 . The solenoid valves  32   a    32   b ,  32   c ,  32   d  are electrically connected to control means  34  of the computer  16  by electric cables  36 . The control means  34  enable the opening or closing of the downstream branches  27   a ,  27   b ,  27   c ,  27   d  of the feed circuit  25  to be controlled independently. 
   An outlet circuit  38  comprising a solenoid outlet valve  40  connected to the control means  34 , is connected to the upstream branch  26  of the feed circuit  25 . 
   The upstream branch  26  of the circuit  25  has a constriction  42  which constitutes means for producing a pressure drop. The dimensions of the constriction  42  are such that the pressure drop in the part  46  of the circuit downstream from the constriction, more simply called the downstream part  46 , is less than 10% of the pressure drop in the constriction  42 . Thus, when the solenoid valve  32   a  is open and the other four are closed, the downstream part  46  comprises the part of the upstream branch  26  located downstream from the constriction  42  and the downstream branch  27   a  of the circuit  25  connected to the tire. It will be remembered that the pressure drop undergone by a fluid circulating in a circuit corresponds to the difference between the pressure of the fluid when it enters the circuit and its pressures when it emerges therefrom. It is generally accepted that the pressure drop is proportional to the length of the circuit, the square of the fluid&#39;s propagation speed in the circuit, and inversely proportional to the diameter of the circuit. 
   The pressure drop in a circuit can be estimated either by direct measurement in the circuit  1  itself, or in a reproduction of the circuit, or by mathematical modelling. 
   The constriction  42  gives rise to most of the pressure drop in the feed circuit  25 . Consequently, the air pressure in the downstream part  46  is essentially uniform, even during inflation phases. A constriction producing such a pressure drop can be obtained, in a pipe of nominal diameter larger than 2 mm, by means of a nozzle of reduced cross-section, for example of diameter 1 mm. 
   The pressure regulation device  23  according to the invention also comprises means  48  for measuring the air pressure in the downstream part  46  of the circuit. These means  48  consist of a classical pressure sensor  48 . The pressure sensor  48  is connected to means  49  for analyzing the evolution of the pressure measured by the sensor  48 . The analysis means  49  are part of the computer  16  and are connected to the tire pressure estimation means  22 . Below, the operation of the device  23  for measuring and regulating the pressure of the vehicle&#39;s tires will be described with reference to  FIGS. 3 to 6 . As mentioned earlier, in most cases the tire pressure is estimated by the means  22  from the comparison means  20 . In the remaining cases the tire pressure estimation means  22  use the pressure regulation device  23  according to the invention. 
   Below, a more detailed description is given of the process for pressure measurement and regulation by means of the first embodiment of the regulation device  23  according to the invention. This process makes it possible to:
         check that the pressure in the tire is at least equal to a predetermined pressure threshold P 0 ;   measure the pressure in the tire; or   inflate the tire.       

   The regulation device  23  according to the first embodiment of the invention enables independent action on any of the vehicle&#39;s tires. Consider for example the tire  10   a.    
   To measure and/or regulate the pressure of tire  10   a , the control means  34  of the computer  16  first cause the solenoid valve  32   a  to open and the other solenoid valves  32   b ,  32   c ,  32   d  and if necessary  40  to close. 
   Then, the computer actuates the beginning of the compressed air feed into the circuit  25 . Thanks to the solenoid valves only the downstream branch  27   a  is supplied with air. 
   During the air feed into the circuit  25 , the computer measures the pressure in the circuit by means of the pressure sensor  48 . Thanks to the constriction  42 , it is known that the pressure measured is essentially equal to the pressure exerted upstream from the check valve  30   a , which is therefore subjected on one side to the pressure in the tire  10   a  and on the other side to the pressure in the downstream branch  27   a  measured by the sensor  48 . The relative values of these two pressures determine whether the check valve is open or closed. 
   The evolution of the pressure measured as a function of time is analyzed by the analysis means  49  so as to detect the opening of the check valve  30   a  and/or whether the predetermined pressure threshold P 0  has been exceeded. 
   It is easy to detect the opening of the check valve  30   a  by analyzing the evolution of the slope of the curve giving the pressure measured as a function of time. In effect, when the valve is closed the air source  24  feeds a small volume consisting only of the circuit  25 . The pressure in the circuit  25  measured by the sensor  48  therefore increases very rapidly with time. In contrast, when the check valve is open the air source  24  feeds a large volume comprising both the circuit  25  and the tire  10   a . Since the air source then has to fill a larger volume than when the check valve is closed, the pressure measured by the sensor  48  increases more slowly. Consequently, the means  49  analyze the slope of the curve expressing measured pressure as a function of time to detect the opening of the check valve. 
   Depending on the times when the two events defined earlier are detected, the following four configurations can be encountered. 
   In the case of  FIG. 3 , the first event detected by the analysis means  49 , at time t s , is that the predetermined pressure value P 0  has been exceeded. In this case, since the opening of the check valve has not yet been detected, it is known that the actual pressure P r  in the tire is at least equal to the value P 0 . If this value P 0  is regulated as a minimum admissible pressure value, the air feed into the circuit is stopped. The pressure in the tire is thus estimated without having injected air into the tire. The solenoid outlet valve  40  is then used to depressurize the circuit. 
   In the case of  FIG. 4  the first event detected by the analysis means  49 , at time t s , is also that the predetermined pressure value P 0  has been exceeded. However, if the computer wants to know the exact value of the tire pressure (although it is above the minimum admissible value), it maintains the air feed until, at time t c , the opening of the check valve is detected. The pressure P r  measured at the time t c  is equal to the actual pressure in the tire. The solenoid outlet valve  40  is then used to depressurize the circuit. 
   In the case of  FIG. 5  the first event detected by the analysis means  49  is the opening of the check valve at time t c , before the pressure value P 0  has been reached. If the computer  16  wants to measure the actual pressure in the tire without inflating it, it stops the air source. The pressure P r  measured at time t c  is equal to the pressure in the tire. The solenoid outlet valve  40  is then used to depressurize the circuit. 
   Finally, in the case of  FIG. 6  the first event detected by the analysis means  49  is the opening of the check valve at time t c . The pressure value P rt  measured then is lower than P 0 . The air feed is maintained and the pressure in the tire increases with time.  FIG. 6  shows that during inflation, the pressure measured (represented by a thick curve) is slightly higher than the actual pressure in the tire (represented by a thin curve). This difference is due to the air flow. 
   At a time t s  the pressure measured exceeds the threshold value P 0 . The computer then stops the air feed and the pressure in the circuit and in the tire settles at a value P r2 . Measurement of this equilibrium pressure by the pressure sensor  48  indicates the exact value of the tire pressure. Once this pressure has been measured, the computer actuates the solenoid outlet valve  40  with the result that the pressure in the circuit decreases very rapidly. The pressure difference between the circuit and the tire automatically closes the check valve  30   a.    
   The process just described can be applied to each of the vehicle&#39;s tires by actuating the solenoid valves in succession In particular, to reduce the energy consumed by the air source  24 , the solenoid valves can be acted upon as follows. 
   Assume that the tire  10   a  has been acted upon. The downstream branch  27   a  is therefore pressurized. Rather than reducing the pressure in the downstream branch  27   a  by means of the solenoid outlet valve  40 , the solenoid valve of another tire can be opened, for example solenoid valve  32   b , so as to transfer the pressure from one branch to the other. The abrupt pressure drop of the order of several hundred millibars is enough to close the check valve  30   a . The pressure in the downstream branch  27   b  of tire  10   b  is then increased even before beginning to feed the circuit with air from the air source  24 . This also enables the time during which the downstream branch  27   b  is pressurized to be decreased. 
   According to a second embodiment illustrated in  FIG. 2 , the upstream branch  26  of the feed circuit  25  is connected to two downstream branches  50  and  51 . The downstream branch  50  is connected to the two tires  10   a  and  10   b , and the downstream branch  51  is connected to the two tires  10   c  and  10   d . The solenoid valves  52  and  53  are interposed respectively in the downstream branches  50  and  51 . This special configuration of the regulation device  55  enables the number of solenoid valves in the device to be reduced and consequently reduces its cost. It also enables the pressure of the two tires on a given axis to be equilibrated, as described earlier. In the embodiment shown, the air-passage bearings  28   a  and  28   b  correspond to a drive axle and the bearings  28   c  and  28   d  to a driven axle. 
   Since the tires are connected in pairs to a downstream branch of the feed circuit, opening the electric valve  52  and feeding the circuit from the air source  24  pressurizes both of the check valves  30   a  and  30   b.    
   The analysis means  49  can detect whether neither of the two check valves  30   a  and  30   b  is open, or only one of them is open, or they are both open. Consequently, the means  49  analyze the evolution of the pressure measured by the sensor  48  as a function of time in such manner as to detect the opening of one check valve, the opening of both check valves, or the fact that a predetermined pressure threshold has been exceeded. 
   It is particularly interesting to detect the opening of both check valves, since it is then known that the two tires  10   a  and  10   b  are at the same pressure. 
   Suppose that during the feeding of air, the check valve  30   a  is the first to open. This means that tire  10   a  is less inflated than tire  10   b . Continuing the air feed thus inflates only tire  10   a  until the opening of the check valve  30   b  is detected. The simultaneous inflation of both tires can then continue until the predetermined pressure threshold is reached. 
   The pressure regulation device  55  illustrated in  FIG. 2  does not have a solenoid outlet valve. Closure of a check valve in a downstream branch is thus obtained by diverting the compressed air to another branch. The feed circuit is then depressurized to atmospheric pressure by virtue of a calibrated leak or incomplete air-tightness at the level of the joints between the various elements of the circuit, for example at the hub/transmission link, at the contact face between the wheel and the disc brake, or at the outer diameter of the bearing. Incomplete air-tightness at the level of these joints can be obtained by placing metallic components in close contact, which does not enable perfectly air-tight joints to be obtained. Tests have shown that such leaks amount for example to 2 L/min per wheel, a low value compared with the flow rate from the air source which is perhaps of the order of 20 L/min. 
   This pressure measurement and regulation device  55  shown in  FIG. 2  can of course be associated with means for comparing the rotation speeds of the wheels of a vehicle, as described and illustrated in  FIG. 1 . 
   According to a variant not illustrated, the size of the constriction is such that the pressure drop in the downstream part is less than 10% of the total pressure drop created by the circuit between the air source and the tire, and more preferably is between 3% and 6% of the total pressure drop. 
   Finally, another variant  60  is shown in  FIG. 7 . This figure shows a tire pressure measurement device  70  in which each tire  10   a ,  10   b ,  10   c ,  10   d  comprises a sensor  61   a ,  61   b ,  61   c ,  61   d  measuring its pressure and associated with a regulation device  60 . The sensors are of the usual type comprising means for the radio transmission of the pressure values to a computer in the vehicle; the said computer can be the computer  16 . The regulation device is similar to that illustrated in  FIG. 2 , the only difference being that it has no pressure sensor in the upstream branch of the feed circuit. Neither are any associated analysis means  49  necessary. As before, the constriction in the feed circuit enables the pressure downstream from the constriction to be stable and essentially equal to the pressure in the tire during its inflation. 
   In this variant the inflation phases are advantageously initiated by the measurement of an insufficient pressure in one of the vehicle&#39;s tires. It is therefore of no use to increase the emission frequency of the sensor. The regulation device can be controlled by a given, fixed or variable inflation duration. In particular, that duration can be determined as a function of the increase in pressure to be expected.