Method for controlling a simplified wheel unit belonging to a system for monitoring the pressure of the tyres of a motor vehicle

Abstract

The invention relates to a method for controlling a simplified wheel unit (16a) belonging to a system for monitoring the pressure of the tyres of a motor vehicle (10), characterised in that it controls the wheel unit (16a) at least in a first energy-saving mode in which the wheel unit (16a) acquires the raw pressure measured by the pressure sensor (32) at a first periodicity, which wheel unit (16a) then compares the raw pressure with a predefined threshold pressure range in order to detect a pressure variation, or in a second alert mode that is transient and in which the wheel unit (16a) switches when the raw pressure is measured outside the threshold pressure range.

Description

DESCRIPTION TITLE: Method for controlling a simplified wheel unit belonging to a tire pressure monitoring system for a motor vehicle [Technical field] [1] The present patent application relates to a method for controlling a simplified wheel unit belonging to a tire pressure monitoring system for a motor vehicle. [State of the prior art] [2] For safety purposes, it is known to equip a motor vehicle with a monitoring system known as “TPMS”, the English acronym for “Tyre Pressure Monitoring System”. [3] Such a monitoring system, which is for example described in document FR3045498, generally comprises a central computing unit mounted on the vehicle and wheel units which each equip an associated wheel of the vehicle. [4] The central unit includes an electronic calculator known as “ECU”, the English acronym for “Electronic Control Unit”. [5] Also, the vehicle's central unit is equipped with a radio frequency receiver adapted to communicate with each wheel unit. [6] Each wheel unit is responsible for regularly acquiring the physical quantities representative of the operating parameters of the associated wheel, in particular to detect an anomaly of the associated wheel. [7] Also, the wheel unit transmits, to the vehicle's central unit, messages containing pressure, temperature and acceleration data of the associated wheel, as well as an identification code of the transmitting wheel unit. [8] For this purpose, each wheel unit includes a tire inflation pressure sensor, a temperature sensor, an accelerometer and a radio frequency transmitter. [9] In addition, the wheel unit is equipped with a battery for power supply and a microcontroller comprising a data storage memory and a microprocessor.

[0010] Upon receipt of this data by the vehicle's central unit, in the event of a significant deviation in pressure from the pressure recommended by the manufacturer, the TPMS system will warn the driver of the vehicle that one of the wheels is under-inflated, for example by displaying an alert message on the vehicle's dashboard.

[0011] The alert message specifies the location of the affected wheel, for example the left front wheel.

[0012] Particular attention is paid to the life of the wheel unit battery, which is of the non-rechargeable battery type.

[0013] In fact, when the battery is discharged, the entire wheel unit must be replaced.

[0014] The commonly accepted state of the art for battery life requirement is ten years, or even seven years.

[0015] To achieve this level of lifespan, it is therefore essential to control energy consumption during each phase of use of the wheel unit.

[0016] A major energy consumer identified is the radio frequency communication between the wheel unit and the vehicle's central unit.

[0017] In fact, to ensure proper reception of data, the same radio frequency message is usually sent in bursts, three or four times.

[0018] Generally, to minimize the energy consumption of these TPMS systems, it is known to detect two main operating modes, namely a so-called "rolling" mode during which the vehicle is moving, and a so-called "non-rolling" mode during which the vehicle is stationary.

[0019] The wheel unit implements an automatic standby process during "non-driving" vehicle operating modes, so that the wheel unit does not communicate with the central unit.

[0020] This process thus proposes to concentrate the supervision of the pressure as well as the associated communications during the vehicle's rolling phases.

[0021] The most common way to determine whether the vehicle is drivable or not is to detect the movement of the vehicle using the accelerometer that is integrated into the wheel unit.

[0022] There are two categories of TPMS systems, namely direct systems and indirect systems.

[0023] Direct systems are of the type of TPMS system described previously, that is to say a TPMS system which comprises wheel units each inserted into a wheel of the vehicle, each wheel unit directly measuring the pressure inside the associated tire.

[0024] Conversely, indirect systems are based on analyzing the speed of each wheel using signals from the anti-lock braking system, better known by the acronym ABS.

[0025] To operate, the indirect system requires calibration which asks the driver to initialize the function via the vehicle's multimedia system when the wheels have just been correctly inflated.

[0026] The algorithm implemented by the vehicle's central unit compares the current wheel speed with the reference speed at recommended pressure.

[0027] An increased speed compared to this reference then indicates under-inflation of the wheel concerned.

[0028] The indirect TPMS system will then, if necessary, warn the driver of the vehicle through an alert which is not localized; the driver should check the pressure of each of his wheels.

[0029] Although this indirect TPMS system helps to limit costs by eliminating the need for wheel units, it has the disadvantage of requiring calibration.

[0030] In addition, the indirect TPMS system is less reliable than the direct TPMS system, since the tire pressure measurement is deduced indirectly and not measured directly by means of a sensor provided for this purpose.

[0031] For both types of indirect and direct TPMS systems, the same legislation applies.

[0032] To comply with them, the driver must be warned of under-inflation or of an interruption in monitoring of one or more of these wheels within a given time, for example ten minutes for Europe, or twenty minutes for the United States.

[0033] It should be noted that this requirement is only required during the vehicle's rolling phases. [Statement of the invention]

[0034] The present invention aims in particular to combine the advantages of the two types of direct and indirect TPMS systems, by proposing a direct TPMS system which has a limited cost, high pressure measurement accuracy, as well as high reliability, while offering a sufficient service life for the wheel units.

[0035] This objective, as well as others which will appear on reading the following description, is achieved with a method for controlling a simplified wheel unit belonging to a tire pressure monitoring system for a motor vehicle, said motor vehicle comprising at least: • a wheel equipped with a wheel unit, • a central computing unit, and • a radiofrequency receiver, and said wheel unit comprising at least: • a battery for power supply, • a pressure sensor, • a radiofrequency transmitter, and • a microcontroller equipped with a processor, the method being characterized in that it controls the wheel unit at least: • in a first energy saving mode in which the wheel unit acquires the raw pressure measured by the pressure sensor during an acquisition step, according to a first periodicity, then the wheel unit compares said raw pressure with a predefined range of threshold pressures to detect a pressure variation, during a comparison step, the energy saving mode being the mode adopted by default by the wheel unit, both when the vehicle equipped with said wheel unit is moving and stationary, or • in a second alert mode which is transient and in which the wheel unit switches when the raw pressure is measured outside the said threshold pressure range during the energy saving mode, the alert mode successively executing: - a pressure verification step consisting of measuring a pressure delta over time and assessing whether said pressure delta represents a pressure alert or not, and - a radiofrequency transmission step which is executed if said pressure delta represents a pressure alert, and which comprises the transmission of at least one data frame to the central unit of the associated motor vehicle, said data frame comprising at least one pressure alert information.

[0036] Thus, the wheel unit is driven by default in an energy-saving mode in which the wheel unit is limited to basic, non-energy-consuming operations, which helps preserve the wheel unit's battery.

[0037] In fact, in energy saving mode, the acquisition of raw pressure, i.e. uncompensated, is a value directly from the microcontroller's analog-to-digital converter which requires little energy.

[0038] This low power consumption allows the wheel unit to adopt this energy saving mode whether the vehicle is in "rolling" or "non-rolling" mode, which allows the wheel unit to do without a dedicated accelerometer for detecting vehicle movement.

[0039] According to other optional features of the invention, taken alone or in combination:

[0040] - in the alert mode the processor of the microcontroller adopts a high energy consumption state whereas in the energy saving mode, said processor adopts a low energy consumption state which is less energy-consuming than the high consumption state;

[0041] - in alert mode, the pressure verification step successively includes: • a first phase of measuring the raw pressure, • a second phase of calculating the current pressure which is obtained by compensating said raw pressure according to at least one compensation parameter, • a third phase of calculating said pressure delta which consists of calculating the difference between the current pressure and a reference pressure, the reference pressure being equal to the value of the current pressure calculated during the previous switch to alert mode, and • a fourth phase of comparing said pressure delta with a predefined threshold, the pressure delta representing a pressure alert if the pressure delta is higher than said threshold. This verification step allows a more precise measurement of the pressure than that carried out in the energy saving mode, but in return it requires more energy, which is why the wheel unit only transits into this alert state;

[0042] - said compensation parameter is determined at least as a function of a temperature value measured by a temperature sensor which equips the wheel unit;

[0043] - in the power saving mode, the wheel unit is in a low-frequency listening state in which the wheel unit can be activated by a low-frequency command issued by an external device;

[0044] - the wheel unit is switched from the energy saving mode to the alert mode when the wheel unit receives a low-frequency command which requests a radiofrequency transmission, the wheel unit then executing a step of radiofrequency transmission of at least one data frame to the central unit of the associated motor vehicle, said data frame comprising at least one item of information corresponding to said command;

[0045] - the wheel unit is switched from the energy saving mode to the alert mode according to a second predefined periodicity, the wheel unit then executing a step of radiofrequency transmission of at least one data frame to the central unit of the associated motor vehicle, to guarantee the transmission of at least one data frame regularly over time. This characteristic aims to show the central unit of the vehicle that the radiofrequency communication is working, in particular to avoid a signal of the “silent wheel” type;

[0046] - in the energy saving mode, the method executes a temperature acquisition step during which the wheel unit acquires the temperature measured by a temperature sensor which equips the wheel unit, according to a third periodicity, then during a comparison step the wheel unit compares said temperature with a predefined range of threshold temperatures, and the wheel unit switches from the energy saving mode to a third mode called non-functional when said temperature is measured outside said range of threshold temperatures, the non-functional mode performing a temperature verification step of measuring the temperature again to check whether it is still within said threshold temperature range. This feature is intended in particular to manage an overheating problem of the wheel unit;

[0047] - the wheel unit is switched from the energy saving mode to the non-functional mode according to a fourth predefined periodicity, the non-functional mode then executing a self-diagnostic step which aims to verify the integrity of the wheel unit;

[0048] - the method according to the invention is implemented without means of detecting the movement of the vehicle. Indeed, the implementation of the method according to the invention is independent of the movement of the vehicle, so that it can be implemented without means of detecting movement of the accelerometer type for example.

[0049] The invention also relates to a motor vehicle which comprises at least one central unit and one wheel unit duly programmed to implement the method of the type described above. [Description of the drawings]

[0050] Other characteristics, aims and advantages of the invention will appear on reading the detailed description which follows, for the understanding of which reference will be made to the appended drawings in which:

[0051] [Fig. 1] Figure 1 is a schematic top view of a motor vehicle which comprises a direct TPMS monitoring system which implements a method for controlling a simplified wheel unit according to the invention;

[0052] [Fig. 2] Figure 2 is a flowchart illustrating the method for controlling the wheel units of Figure 1, according to the invention. [Description of embodiments]

[0053] Figure 1 schematically shows a motor vehicle 10 which comprises a central unit 12 and four wheels 14a, 14b, 14c, 14d which are each equipped with a wheel unit 16a, 16b, 16c, 16d respectively.

[0054] In order not to make the description too long, only one wheel unit 16a is described below, the four wheel units 16a, 16b, 16c, 16d having a similar design and operation.

[0055] The wheel unit 16a belongs to a system for monitoring the tire pressure of a motor vehicle known by the English acronym "TPMS", for "Tyre Pressure Monitoring System" in English.

[0056] The central unit 12 of the motor vehicle 10 comprises an electronic calculator (not shown) known as “ECU” for “Electronic Control Unit” in English, and a memory (not shown).

[0057] Also, the central unit 12 includes a radio frequency receiver 20.

[0058] The wheel unit 16a comprises a housing which contains a microcontroller 22 equipped with a processor, a battery 24, a memory 26 and a radio frequency transmitter 28.

[0059] The transmitter 28 of the wheel unit 16a is adapted to communicate and transmit messages to the central unit 12 via the receiver 20 of the central unit 12.

[0060] In addition, the wheel unit 16a comprises a set of sensors dedicated to measuring operating parameters of the wheel unit 16a.

[0061] This set of sensors comprises a first temperature sensor 30 capable of measuring a temperature parameter and a second pressure sensor 32 capable of measuring the inflation pressure of the tire of the associated wheel 14a.

[0062] The measurements taken by the sensors can be transmitted to the central unit 12 of the motor vehicle 10 via messages sent by the transmitter 28 of the associated wheel unit 16a.

[0063] Note that the 16a wheel unit is a simplified 16a wheel unit that lacks an accelerometer.

[0064] Figure 2 shows a state machine which illustrates the method for controlling the simplified wheel unit 16a according to the invention.

[0065] A state machine is a mathematical model of computation capable of being in a finite number of modes, or states, but at any given time being in only one mode at a time.

[0066] The mode the state machine is in is called the "current mode," or "current state."

[0067] The transition, or switching, from one mode to another is activated by an event or condition.

[0068] In Figure 2, the boxes represent each possible mode and the arrows represent the transitions between modes.

[0069] The method according to the invention controls the wheel unit 16a in two main operating modes, a first energy saving mode M1 and a second alert mode M2.

[0070] The energy saving mode M1 is the mode adopted by default by the wheel unit 16a, whether the motor vehicle 10 is moving or stationary.

[0071] In the energy saving mode M1, the processor of the microcontroller 22 adopts a low energy consumption state which makes it possible to preserve the battery 24 of the wheel unit 16a.

[0072] Also, in the energy saving mode M1, the wheel unit 16a acquires the raw pressure Pb measured by the pressure sensor 32 during a first acquisition step E1M1.

[0073] The E1M1 pressure acquisition step is produced regularly, following a first periodicity T 1.

[0074] According to an exemplary implementation of the invention, the first periodicity T1 is sixteen seconds.

[0075] Following the acquisition step E1M1, the wheel unit 16a executes a second comparison step E2M1 which compares the measured raw pressure Pb with a predefined range of threshold pressures Ps, to detect a pressure variation outside the range.

[0076] If the measured raw pressure Pb is outside the threshold pressure range Ps, then the wheel unit 16a switches to alert mode M2 ​​transiently.

[0077] It should be noted that the E1 M1 pressure acquisition and E2M1 comparison steps have a low energy cost, because they involve measuring and comparing raw, so-called uncompensated, values ​​with a predefined range of values, which is sufficient to detect a pressure variation.

[0078] In fact, the raw measured pressure values ​​come directly from the analog-to-digital converter, and in return from the comparison step E2M1 the microcontroller 22 produces a boolean which translates an “alert” state or a “non-alert” state.

[0079] The M2 alert mode performs a pressure verification step E1M2 consisting of measuring a pressure delta dP over time and evaluating whether the pressure delta dP represents a pressure alert or not.

[0080] For this purpose, the pressure verification step E1 M2 comprises a first phase of measuring the raw pressure Pb by means of the pressure sensor 32 and measuring the temperature Tm by means of the temperature sensor 30, followed by a second phase of calculating the current pressure Pcurrent.

[0081] The second phase of calculating the current pressure Pcurrent is obtained by compensating the raw pressure Pb according to at least one compensation parameter.

[0082] According to an exemplary implementation of the invention, the compensation parameter is the temperature Tm measured previously during the phase of measuring the temperature Tm.

[0083] Indeed, the pressure inside a tire varies according to its internal temperature, it is therefore advantageous to compensate the measured raw pressure Pb to obtain a current pressure Pcurrent which is more precise than an uncompensated raw pressure

[0084] Also, the pressure verification step E1M2 includes a third phase of calculating the pressure delta dP which consists of calculating the difference between the current compensated pressure Pcurrent and a reference pressure P re t.

[0085] The reference pressure P ret is equal to the value of the current pressure Pcurrent calculated during the previous passage of the wheel unit 16a in alert mode M2.

[0086] In other words, the pressure delta dP calculation phase consists of calculating the difference between the current pressure Pcurrent during alert mode n, and the current pressure Pcurrent calculated during the previous alert mode n-1.

[0087] Finally, the pressure verification step E1M2 includes a fourth phase of comparison of the pressure delta dP with a predefined threshold S1.

[0088] The pressure delta dP is considered to represent a pressure alert if the pressure delta dP is greater than the threshold S1.

[0089] For example, the predefined threshold S1 is equal to 10 kPa.

[0090] Still during the M2 alert mode, a radiofrequency transmission step E2M2 is executed if the pressure delta dP calculated previously represents a pressure alert.

[0091] The E2M2 radiofrequency transmission step comprises the transmission of a burst of data frames to the central unit 12 of the motor vehicle 10.

[0092] Each data frame includes in particular pressure alert information, the central unit 12 thus informed will be able to display an alert message on the dashboard of the motor vehicle 10 to warn the driver of an inflation anomaly of a wheel of the vehicle.

[0093] Following the radiofrequency transmission step E2M2, the wheel unit 16a switches to its energy saving mode M1.

[0094] It will be noted that during the E2M2 radiofrequency transmission step, the data frames sent to the central unit 12 can do without transmitting a wake-up pattern from the central unit 12 aimed at informing of a start of communication.

[0095] Indeed, it is considered that the central unit 12 is necessarily awake during the driving phases of the vehicle 10, that is to say the phase where the regulation applies, and that if the central unit 12 is in the sleep phase during the stopping phases of the vehicle 10, the data frames carrying the pressure alert will be received from the next driving phase, which is sufficient.

[0096] We have seen that, according to a first scenario, the wheel unit 16a switches from its energy saving mode M1 to its alert mode M2 ​​when the measured raw pressure Pb is outside the threshold pressure range Ps.

[0097] According to a second scenario, the wheel unit 16a switches from the energy saving mode M1 to the alert mode M2 ​​when the wheel unit 16a receives a low frequency command by radio frequency provided for this purpose.

[0098] For this purpose, in energy saving mode M1, the wheel unit 16a is in a low frequency listening state, that is to say that the wheel unit 16a can be activated by a low frequency command which is a signal emitted by an external device, generally with the aim of forcing the wheel unit 16a to send back radio frequency messages.

[0099] Thus, when the wheel unit 16a receives a low-frequency command, the latter switches to alert mode M2 ​​and executes a radiofrequency transmission step E2M2 of at least one data frame to the central unit 12 of the motor vehicle 10, the data frame comprising at least one item of information corresponding to the low-frequency command received.

[0100] Following the radiofrequency transmission step E2M2, the wheel unit 16a switches to its energy saving mode M1.

[0101] Finally, according to a third scenario, the wheel unit 16a switches from the energy saving mode M1 to the alert mode M2 ​​according to a second predefined periodicity T2, to guarantee the transmission of at least one data frame by radio frequency regularly over time.

[0102] To this end, according to this third scenario, the wheel unit 16a executes a step of radiofrequency transmission E2M2 of at least one data frame to the central unit 12 of the motor vehicle 10.

[0103] Since the movement detection is not carried out by the TPMS system, since the wheel unit 16a does not have an accelerometer, this third scenario of regular radiofrequency emission is constantly maintained even during the stopping phases of the motor vehicle 10.

[0104] Thus, radiofrequency emissions are not limited to the driving phases of the motor vehicle 10.

[0105] According to an example of implementation, the second periodicity T2 is five minutes, so as to ensure at least two radiofrequency transmissions within a period of ten minutes, in order to meet the most restrictive regulatory deadlines.

[0106] Following the radiofrequency transmission step E2M2, the wheel unit 16a switches to its energy saving mode M1.

[0107] In the alert mode, the processor of the microcontroller 22 adopts a so-called high power consumption state while in the power saving mode, the processor adopts a low power consumption state which is less energy-consuming than the high power consumption state.

[0108] The current consumption ratio is approximately one to eight thousand between power saving mode and alert mode.

[0109] According to another aspect of the method according to the invention, the wheel unit 16a can switch to a third mode called “non-functional” M3.

[0110] Indeed, in the energy saving mode M1, the wheel unit 16a acquires the temperature Tm measured by the temperature sensor 30 during a third acquisition step E3M1.

[0111] The E3M1 temperature acquisition step is produced regularly, following a third periodicity T3.

[0112] According to an exemplary implementation of the invention, the third periodicity T3 is sixty-four seconds.

[0113] Following the temperature acquisition step E3M1, the wheel unit 16a executes a fourth comparison step E4M1 which compares the measured temperature Tm with a predefined temperature range Ts which corresponds to an operational temperature range in which the wheel unit 16a is suitable for operating.

[0114] If the measured temperature Tm is outside the temperature range Ts, then the wheel unit 16a switches to the non-functional mode M3 transiently.

[0115] The non-functional mode M3 performs a temperature verification step E1M3 which consists of measuring the temperature Tm again and checking whether the measured temperature Tm is outside the temperature range Ts.

[0116] If the temperature Tm is still outside the temperature range Ts, then the wheel unit 16a remains in the non-functional mode M3.

[0117] Conversely, if the temperature Tm is within the operational temperature range Ts, then the wheel unit 16a switches to the energy saving mode M1.

[0118] In addition, the wheel unit 16a switches from the energy saving mode M1 to the non-functional mode M3 according to a fourth predefined periodicity T4, the non-functional mode M3 then executing a self-diagnostic step E2M3 which aims to verify the integrity of the regular wheel unit.

[0119] The fourth periodicity T4 is for example set at one hour.

[0120] For example, the self-diagnostic step E2M3 may consist of a verification of the memory of the wheel unit 16a, and / or a verification of the state of the battery and / or a verification of the calibration of the clock signals of the wheel unit 16a and / or even a verification of a software error.

[0121] Also, in non-functional mode M3, the wheel unit 16a is in a low-frequency listening state, i.e. the wheel unit 16a can be requested to send the self-diagnostic data by radio frequency during a part return.

[0122] Apart from these radio frequency transmissions, no periodic radio frequency transmissions are permitted.

[0123] The transition from the non-functional mode M3 to the energy-saving mode M1 is the end of the activities of the non-functional mode M3 without the presence of an error and with a measured temperature Temp belonging to the operational temperature range Ts.

[0124] Also, apart from the three modes M1, M2, M3 described previously, and in order to guarantee specific provisions associated with different phases in the life of the unit wheel 16a, the wheel unit 16a is in a fast low frequency listening state, in the production phase, and any spontaneous radio frequency transmission during transport and / or storage of the wheel unit 16a is prevented, in order to preserve the battery of the wheel unit 16a.

[0125] For this purpose, the method according to the invention makes it possible to modify a phase variable which is stored in the flash memory of the wheel unit 16a, so as not to be lost in the event of resetting the wheel unit 16a.

[0126] Three phases are thus envisaged, following one another in a pre-established and unalterable order, namely a production phase, followed by a transport and storage phase, followed by an operational phase.

[0127] This phase variable is modified only by the use of an identified low frequency command.

[0128] Each time this low frequency command is received, we move on to the next phase by updating the phase variable.

[0129] When the third and final phase, i.e. the operational phase, is reached, a new low frequency reception will cause the restart in the production phase, and so on.

[0130] In the production phase, the wheel unit 16a is in a state of rapid low frequency listening, that is to say with a high recurrence assimilated to permanent listening.

[0131] Among the advantages offered by the present invention, it will be noted that the method according to the invention does not require measurement of the acceleration experienced by the wheel unit 16a, thanks to which the method according to the invention is suitable for being implemented by a wheel unit which is devoid of an accelerometer and which therefore has a reduced cost.

[0132] Also, given the simplification of the 16a wheel unit, it is possible to reduce the length of the standard radio frequency frame sent by the 16a wheel unit, by removing several fields that have become superfluous, such as acceleration (Sbits), location information (3bits), frame number (2bits) and finally the function code (reduction to 2bits rather than 4bits).

[0133] This change in length thus makes it possible to minimize the time required for the radiofrequency transmission of the frame between the wheel unit 16a and the central unit 12, from 10.52 milliseconds to 8.85 milliseconds.

[0134] The energy consumption of the 16a wheel unit is therefore optimized.

[0135] In addition, the method according to the invention offers increased accuracy and reliability of the underpressure alert compared to an indirect TPMS system.

[0136] Similarly, the method according to the invention offers an improvement in the user experience because no initialization of the TPMS system is required after re-inflation of the wheel, unlike the indirect TPMS system.

[0137] Finally, the method according to the invention simplifies the software embedded in the wheel unit 16a with the aim of reducing customer / user returns, thus minimizing the associated costs.

Claims

Claims

1. Method for controlling a simplified wheel unit (16a) belonging to a tire pressure monitoring system of a motor vehicle (10), said motor vehicle (10) comprising at least: • a wheel (14a) equipped with a wheel unit (16a), • a central computing unit (12), and • a radiofrequency receiver (20), and said wheel unit (16a) comprising at least: • a battery (24) for power supply, • a pressure sensor (32), • a radiofrequency transmitter (28), and • a microcontroller (22) equipped with a processor, the method being characterized in that it controls the wheel unit (16a) at least: • in a first energy saving mode (M1) in which the wheel unit (16a) acquires the raw pressure Pb measured by the pressure sensor (32) during an acquisition step (E1 M1), according to a first periodicity T1, then the wheel unit (16a) compares said raw pressure Pb with a predefined range of threshold pressures Ps to detect a pressure variation, during a comparison step (E2M1), the energy saving mode (M1) being the mode adopted by default by the wheel unit (16a), both when the vehicle equipped with said wheel unit (16a) is moving and stationary, or • in a second alert mode (M2) which is transient and in which the wheel unit (16a) switches when the raw pressure Pb is measured outside said threshold pressure range Ps during the energy saving mode (M1), the alert mode (M2) successively executing: - a pressure verification step (E1M2) consisting of measuring a pressure delta dP over time and evaluating whether said pressure delta dP represents a pressure alert or not, and - a radiofrequency transmission step (E2M2) which is executed if said pressure delta dP represents a pressure alert, and which comprises the transmission of at least one data frame to the central unit (12) of the associated motor vehicle (10), said data frame comprising at least one pressure alert information.

2. Method for controlling a simplified wheel unit (16a) according to claim 1, characterized in that in the alert mode (M2) the processor of the microcontroller (22) adopts a high power consumption state while in the power saving mode (M1), said processor adopts a low power consumption state which is less energy consuming than the high power consumption state.

3. Method for controlling a simplified wheel unit (16a) according to any one of the preceding claims, characterized in that in the alert mode (M2), the pressure verification step (E1M2) successively comprises: • a first phase of measurement of the raw pressure Pb, • a second phase of calculating the current pressure Pcurrent which is obtained by compensating said raw pressure Pb according to at least one compensation parameter, • a third phase of calculating said pressure delta dP which consists of calculating the difference between the current pressure Pcurrent and a reference pressure P re t, the reference pressure P re t being equal to the value of the current pressure Pcurrent calculated during the previous switch to alert mode (M2), and • a fourth phase of comparing said pressure delta dP with a predefined threshold S1, the pressure delta dP representing a pressure alert if the pressure delta dP is greater than said threshold S1.

4. Method for controlling a simplified wheel unit (16a) according to claim 3, characterized in that said compensation parameter is determined at least as a function of a temperature value measured by a temperature sensor (30) which equips the wheel unit (16a).

5. A method for controlling a simplified wheel unit (16a) according to any one of the preceding claims, characterized in that in the energy saving mode (M1), the wheel unit (16a) is in a low-frequency listening state in which the wheel unit (16a) can be activated by a low-frequency command issued by an external device.

6. Method for controlling a simplified wheel unit (16a) according to claim 5, characterized in that the wheel unit (16a) is switched from the energy saving mode (M1) to the alert mode (M2) when the wheel unit (16a) receives a low-frequency command which requests a radiofrequency transmission, the wheel unit (16a) then executing a step of radiofrequency transmission of at least one data frame to the central unit (12) of the associated motor vehicle (10), said data frame comprising at least one item of information corresponding to said command.

7. Method for controlling a simplified wheel unit (16a) according to any one of the preceding claims, characterized in that the wheel unit (16a) is switched from the energy saving mode (M1) to the alert mode (M2) following a second predefined periodicity T2, the wheel unit (16a) then executing a radiofrequency transmission step (E2M2) of at least one data frame to the central unit (12) of the associated motor vehicle (10), to guarantee the transmission of at least one data frame regularly over time.

8. Method for controlling a simplified wheel unit (16a) according to any one of the preceding claims, characterized in that in the energy saving mode (M1), the method executes a temperature acquisition step (E3M1) during which the wheel unit (16a) acquires the temperature Tm measured by a temperature sensor (30) which equips the wheel unit (16a), according to a third periodicity T3, then during a comparison step (E4M1) the wheel unit (16a) compares said temperature Tm with a predefined range of threshold temperatures Ts, and in that the wheel unit (16a) switches from the energy saving mode (M1) to a third so-called non-functional mode (M3) when said temperature Tm is measured outside said range of threshold temperatures Ts,the non-functional mode (M3) performing a temperature verification step (E1M3) consisting of measuring the temperature again to check whether it is still within said threshold temperature range Ts.,

9. Method for controlling a simplified wheel unit (16a) according to claim 8, characterized in that the wheel unit (16a) is switched from the energy saving mode (M1) to the non-functional mode (M3) according to a fourth predefined periodicity T4, the non-functional mode (M3) then executing a self-diagnostic step (E2M3) which aims to verify the integrity of the wheel unit (16a).

10. Method for controlling a simplified wheel unit (16a) according to any one of the preceding claims, characterized in that it is implemented without means for detecting movement of the vehicle.

11. A motor vehicle (10) which comprises at least one central unit (12) and one wheel unit (16a) duly programmed to implement the method according to any one of claims 1 to 10.

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