Low-frequency emission electronic unit emitting to a mobile wheel electronic unit of a vehicle and associated low-frequency signal transmission method

The present invention relates to an electronic unit emitting low-frequency waves to a mobile wheel electronic unit of a vehicle and to a method of transmitting low-frequency signals between said emission electronic unit (hereinafter called “emitting unit”) and the receiving wheel electronic unit (hereinafter called “wheel unit”).

The wheel electronic units (called “wheel units”) currently have the functionality of informing a centralized electronic control unit (hereinafter called “central unit”) concerning various parameters relating to the wheel, such as the tire pressure, the temperature of the gas inside of the tire or wheel temperature, the footprint of the tire, for example the length of this print along the plane of the wheel. These wheel units 13 (cf. FIG. 1 ) are generally fitted to each wheel 11 of the vehicle 10 (cf. FIG. 3 ) and are generally fixed inside the tire against its tread, and are provided with means that make it possible to record the moment when this tread comes into contact with the ground S and the moment when it leaves the ground S, by the induced radial displacement of the tread. These means are, for example, an accelerator or an impact sensor or similar associated with the wheel unit 13 , which measures, in the case of the accelerometer for example, the difference in radial acceleration when it enters into contact with the ground S and leaves this contact.

The wheel unit 13 is provided with at least one pressure sensor 17 (often also a temperature sensor), and also comprises (in a nonlimiting manner):

a microprocessor, an antenna 15 for receiving low-frequency LF signals, an antenna for emitting radiofrequency RF signals (not represented) (cf. FIG. 3 ), and a battery (not represented) powering all of these elements.

The wheel unit 13 can also comprise other sensors as cited above, for example an accelerometer.

The central unit 12 , mounted on the vehicle V, is for its part provided with at least:

a radiofrequency receiving antenna 16 (cf. FIG. 3 ), a computer with microprocessor,

and it is linked electrically to four low-frequency emission electronic units 20 (cf. FIG. 3 ), that is to say to four emitting units 20 .

This central unit 12 is powered by the battery of the vehicle V.

Each of the emitting units 20 is situated in a fixed manner on the vehicle V close to a wheel unit 13 .

Each emitting unit 20 comprises a low-frequency emission antenna, and a microcontroller linked electrically to said emission antenna. The emitting unit 20 can, in certain cases, comprise only the low-frequency emission antenna, linked electrically to the computer, situated in the central unit 12 .

At fixed frequency, the central unit 12 controls the sequential sending of low-frequency LF interrogation signals via the emitting units to each of the wheel units 13 .

Each wheel unit 13 then transmits sequentially, one after the other, radiofrequency RF signals (generally high frequency) to the central unit 12 in order for the latter to inform the driver of any abnormal measured parameters, and also in order for this central unit 12 to be able to locate the position of each wheel unit 13 on the vehicle V throughout the life of the tire associated with the wheel 11 , and do so even if the position of the wheel 11 is changed on the vehicle V.

During the rotation of a wheel 11 , and over one revolution of the wheel 11 , there are generally parts of trajectories of the wheel unit 13 in which the reception by the wheel unit 13 of the LF signals sent by the closest emitting unit 20 does not work, called low-frequency rupture zones Zo (cf. FIG. 1 ), which correspond to an RF signal reception rupture zone. This can be true for each wheel 11 of the same vehicle V in a different and unpredictable manner. There is, however, by convention, a limited acceptance of the number and the duration of the rupture zones Zo for a wheel 11 revolution. For example, a rupture zone Zo of approximately 1° maximum is generally accepted for each wheel 11 revolution. In certain particular cases, this number may be raised to two rupture zones Zo each of the order of 1° maximum for each wheel 11 revolution.

FIG. 2 illustrates an example of intensity RFi of the low-frequency LF signal received by the reception antenna 15 of the wheel unit 13 according to the angle of rotation θ of the wheel, over a complete wheel revolution (360°), also called reception pattern. In this example, the rupture zone Zo appears in the regions of 225°, the intensity RFi of the low-frequency LF signal is then insufficient for the wheel unit 13 to receive the LF signal.

A vehicle V without rupture zone Zo and in which the rate of LF reception by the wheel unit 13 reaches 100% is in fact not representative of the reality. In effect, the wheel unit 13 comprises a single low-frequency reception antenna 15 , and the emitting unit 20 , for its part, has a single low-frequency LF signal emitting antenna, generally in the form of a longitudinal copper coil surrounding a ferrite, which emits LF signals in a single direction. The rupture zone Zo corresponds to a momentary position of the wheel unit 13 on the wheel 11 , for which the orientation of the wheel unit 13 is such that the direction of reception of the receiving antenna 15 of said wheel unit 13 does not allow the reception of the low-frequency LF signals sent by the emitting unit 20 .

One prior art solution consists in equipping the emitting unit 20 with a second emission antenna, fixed at right angles to the emitting antenna already present in the emitting unit 20 . The two antennas have emission directions at right angles. This makes it possible to increase the probability of reception of the LF signals by the wheel unit 13 and reduce the rupture zone Zo. With a second antenna, the rate of reception of the LF signals by the wheel unit 13 comes close to 100%.

However, the addition of a second low-frequency antenna in the emitting unit 20 with its associated electronic control circuit represents a not-inconsiderable cost. The emitting unit 20 also becomes more bulky because of the additional space allocated for the second antenna, at right angles to the antenna already present, so its incorporation in the vehicle V becomes less easy.

Another prior art solution consists in equipping the wheel unit 13 with a second LF signal receiving antenna, at right angles to the receiving antenna 15 already present in the wheel unit 13 . However, this addition represents a real bulk drawback, and the incorporation of the wheel unit 13 in the tire 11 against the tread becomes difficult.

The present invention proposes an electronic unit emitting low-frequency waves 20 , fixed to a vehicle V, to a mobile wheel electronic unit of said vehicle V and a transmission method applicable to one or more low-frequency LF signals between said emission electronic unit 20 and the wheel unit 13 that makes it possible to improve the efficiency of reception of said low-frequency waves by the wheel unit 13 . Improving the receiving efficiency amounts to ensuring that the low-frequency LF signals transmitted can be statistically received by the wheel unit 13 within a defined minimum time period, and regardless of the speed of the vehicle up to a predefined maximum speed, for example 250 km/h.

The invention proposes a low-frequency emission electronic unit emitting to a mobile wheel electronic unit of a vehicle, fixed to said wheel, said low-frequency emission electronic unit comprising:

a microcontroller, a first low-frequency emission antenna, oriented along an axis, connected to the microcontroller, having a power supply voltage, and emitting a first low-frequency field,

said low-frequency emission electronic unit being noteworthy in that it further comprises:

a second passive low-frequency antenna arranged along the axis of the first antenna, situated in a zone of reception of the first low-frequency field, regardless of the power supply voltage of the first antenna, and comprising a first part and a second part, linked electrically together, separated by a gap having a length, the two parts being adapted to emit low-frequency fields of opposite directions, and directed toward one another, means for adapting a frequency of the second antenna to the frequency of the first antenna, means for regulating the power supply voltage of the first antenna; means for controlling the adaptation means and the regulation means.

Shrewdly, the first antenna and the second antenna are coaxial and wound around the same ferrite.

In a preferential embodiment, the voltage regulation means comprise:

a first two-way switch, connected on one side to a voltage generator incorporated in the microcontroller, and connected on the other side to: a first circuit of nominal voltage, comprising a first resistor, a second circuit of voltage lower than the nominal voltage, comprising a second resistor;

the first switch having a first position in which the first antenna is connected to the first circuit and a second position in which the first antenna is connected to the second circuit.

Also, the adaptation means comprise

a second switch, a frequency adaptation circuit comprising:

a capacitor, a third resistor,

the second switch having a closed position in which the second antenna is connected to the adaptation circuit and an open position in which the second antenna is disconnected from the adaptation circuit.

Preferentially, a length of the first part is equal to a length of the second part and the length of the gap is between ⅛ th and ⅝ th of the length of the first part or of the length of the second part.

The invention relates also to a method for transmitting low-frequency signals from a low-frequency emission electronic unit to a mobile wheel electronic unit of a vehicle, fixed to said wheel, said low-frequency emission electronic unit comprising:

a microcontroller, a first low-frequency emission antenna oriented along an axis, connected to the microcontroller, having a power supply voltage, and emitting a first low-frequency field,

the method being noteworthy in that, in a preliminary step, the low-frequency emission electronic unit is equipped:

with a second passive low-frequency antenna arranged along the axis of the first antenna, situated in a zone of reception of the first low-frequency field, regardless of the power supply voltage of the first antenna, and comprising a first part and a second part, linked electrically together, separated by a gap having a length, the two parts being adapted to emit low-frequency fields of opposite directions, and directed toward one another, means for adapting a frequency of the second antenna to the frequency of the first antenna, means for regulating the power supply voltage of the first antenna; making it possible to regulate the power supply voltage of the first antenna either to a nominal voltage or to a voltage lower than the nominal voltage, means for controlling the adaptation means and the regulation means,

said method comprising the following steps:

step 1: activation of the regulation means in order to power the first antenna with a nominal voltage for a first predetermined duration, step 2: deactivation of the regulation means, step 3: activation of the regulation means in order to power the first antenna with a voltage lower than the nominal voltage and activation of the adaptation means simultaneously for a second predetermined duration, step 4: deactivation of the regulation means and deactivation of the adaptation means simultaneously, step 5: repetition of the steps 1 to 4.

Preferentially:

step 1 consists in connecting the first switch to the circuit of nominal voltage, step 2 consists in disconnecting the first switch from the circuit of nominal voltage, step 3 consists in connecting the first switch to the circuit of voltage lower than the nominal voltage and in closing the second switch, step 4 consists in disconnecting the first switch from the circuit of voltage lower than the nominal voltage simultaneously with the opening of the second switch.

The invention applies also to any system for monitoring the pressure of the tires, comprising a central unit, at least one wheel electronic unit, and at least one low-frequency emission electronic unit according to any one of the features listed above.

Finally, the invention relates to any motor vehicle comprising a low-frequency emission electronic unit according to one of the features listed above.

Other features and advantages of the invention will become apparent on reading the following description and on studying the attached drawings in which:

FIG. 1 , explained previously, represents a schematic view of a wheel equipped with a wheel unit 13 , illustrating a rupture zone Zo, according to the prior art,

FIG. 2 , explained previously, represents a schematic view of the intensity of the low-frequency signal received by the wheel unit according to the angle of rotation of the wheel, according to the prior art,

FIG. 3 represents a schematic view of a vehicle equipped with wheel units and a central unit,

FIG. 4 represents a schematic view of a low-frequency emission electronic unit according to the invention,

FIG. 5 represents a schematic view of the first antenna and of the second antenna of the low-frequency emission electronic unit according to the invention,

FIG. 6 represents a schematic view of the intensity of the low-frequency signal received by the wheel unit, according to the invention.

According to the embodiment represented in FIG. 3 , a vehicle 10 is conventionally provided with four tires 11 . Each of these tires 11 is equipped with a wheel unit 13 . The vehicle 10 is also provided with a central unit 12 and four low-frequency emission electronic units 20 .

The central unit 12 , the wheel units 13 and the emitting units 20 belong to a system for monitoring the pressure of the tires 11 . This system is adapted to regularly measure the pressure (and the temperature) prevailing in the tires, so as to inform the driver of the vehicle 10 of any abnormality. Each wheel unit 13 comprises, for this purpose, a pressure sensor 17 and a temperature sensor (not represented). Since this system is known per se, it will not be detailed here.

The emitting units 20 each send, in turn, at the request of the central unit 12 , an interrogation method to the wheel unit 13 located closest. This interrogation method is sent by low-frequency waves.

Wheel units 13 then measure the temperature and the pressure prevailing in the tires 11 using the pressure 17 and temperature sensors and emit the measured values (possibly preprocessed) to the central unit 12 by RF (radiofrequency) signals of frequency f of the order of 433 MHz or 315 MHz, using their radiofrequency emission antenna 15 . The central unit 12 receives, using a radiofrequency antenna 16 , the RF signals emitted by the wheel units 13 , processes them and informs the driver of any abnormality.

It should be noted that the central unit 12 and the wheel units 13 are not connected together by a wired network. Similarly, the emitting units 20 and the wheel units 13 are not connected together by a wired network.

As explained previously, the wheel unit 13 of the prior art, equipped with just one antenna 15 has the drawback of having a rupture zone Zo (cf. FIG. 1 ) on the wheel 11 in which the low-frequency LF signals emitted by the antenna of the emitting unit 20 are not received by the wheel unit 13 .

To mitigate this drawback, the invention proposes an emitting unit 20 ′ as illustrated in FIG. 4 . The emitting unit 20 ′ comprises, as in the prior art:

a microcontroller 30 , a first low-frequency emission antenna B 1 of frequency f, in the form of a copper coil, surrounding a ferrite F′, extending along an axis Y. Said first antenna B 1 is powered on one side with alternating voltage Vdd by a voltage generator G incorporated in the microcontroller 30 and on the other side said first antenna B 1 is connected to a capacitor C 1 , which is in turn linked to the ground. The capacitor C 1 makes it possible to adjust the emission frequency f of said first antenna B 1 .

For explanatory purposes, it is considered in this example that the emitting unit 20 ′ comprises a microcontroller 30 which manages the emission of the low-frequency signals by the first antenna B 1 . Generally, the emitting unit 20 ′ comprises only one emitting antenna B 1 which is linked to the microcontroller of the central unit 12 , said microcontroller managing the emission of the low-frequency signals by the emitting unit 20 ′.

The first antenna B 1 generates a first low-frequency field D 1 directed along the axis Y (cf. FIG. 4 ).

According to the invention, the emitting unit 20 ′ further comprises:

a second low-frequency emission antenna B 2 of frequency f′, means M 1 for adapting the frequency f′ of the second antenna B 2 to the frequency f of the first antenna B 1 , means M 2 for regulating the power supply voltage Vdd of the first antenna B 1 , control means M 3 , adaptation means M 1 and regulation means M 2 , for example incorporated in the microcontroller 20 ′.

The second antenna B 2 is a passive antenna. It is not supplied with voltage. It, for example, takes the form of a copper winding.

The second antenna B 2 is situated in the zone of reception of the low-frequency field D 1 emitted by the first antenna B 1 , regardless of the power supply voltage Vdd of the first antenna B 1 .

The second antenna B 2 consists of a single copper wire. It comprises two parts B 2 a and B 2 b , for example two copper windings, linked electrically together by the copper wire and separated by a gap E of length l. The two parts, the first winding B 2 a and the second winding B 2 b are designed or adapted, when the second antenna B 2 emits low-frequency waves (the conditions of emission of the second antenna B 2 are explained below), to generate low-frequency fields C 2 a , C 2 b of opposite directions and directed toward one another.

For example, the first winding B 2 a of length l 1 is produced in a first direction of winding, and the second winding B 2 b of length l 2 is produced in the direction opposite the first direction of winding. The second winding B 2 b is separated from the first winding B 2 a by the gap E of length l, and linked electrically to the first winding by said copper wire along said gap E. More specifically, the copper wire is wound neither in the first direction nor in the opposite direction at the gap E. Preferentially, the lengths of the two windings B 2 a , B 2 b are equal to each other, l 1 equals l 2 , and the length l of the gap E is between ⅛ th and ⅝ th of the length l 1 of the first winding B 2 a , or of the length l 2 of the second winding B 2 b (cf. FIGS. 4 and 5 ).

As illustrated in FIG. 5 , the first winding B 2 a generates a first low-frequency field C 2 a directed along the axis Y, toward the gap E. The second winding B 2 b generates a second low-frequency field C 2 b , the direction of which, along the axis Y, is opposite that of the first low-frequency field C 2 a and directed toward the gap E.

The two low-frequency fields C 2 a , C 2 b are directed toward one another; they meet at the gap E and generate a second low-frequency field D 2 and a third low-frequency field D 2 ′ at right angles to the axis Y and oriented at 180° to one another (cf. FIG. 5 ).

Thus, the second antenna B 2 , through its geometry (two windings B 2 a , B 2 b producing fields directed toward one another), emits two low-frequency fields D 2 and D 2 ′ at right angles to the axis Y, that is to say at right angles to the first low-frequency field D 1 emitted by the first antenna B 1 .

The means M 2 for regulating the power supply voltage Vdd upstream of the first antenna B 1 consists of a first two-way switch S 1 linked on one side to the voltage generator G, and on the other side, depending on the position of said switch S 1 , to one of two circuits mounted in parallel, both linked to a first end of the first antenna B 1 (cf. FIG. 4 ):

a first circuit of nominal voltage, comprising a first resistor R 1 , a second circuit of voltage lower than the nominal voltage comprising a second resistor R 2 .

With R 2 <<R 1 .

In another embodiment, the means M 2 for regulating the power supply voltage Vdd can comprise a variable resistor making it possible to adjust the power supply voltage either to the nominal voltage or to the voltage lower than the nominal voltage.

Thus, when the first switch is connected to the first circuit of nominal voltage, the first antenna B 1 is powered by a nominal voltage. The first antenna B 1 emits the first low-frequency field D 1 to the central unit 12 , as in the prior art.

When the first switch S 1 is connected to the second circuit, the first antenna B 1 is powered by a voltage very much lower than the nominal voltage. In this case, the first antenna B 1 then emits a new low-frequency field D 1 ′ of short range, insufficient to be received by the wheel unit 13 , but of sufficient range to be received by the second antenna B 2 , situated in proximity to the first antenna B 1 . In effect, the second antenna B 2 is situated in the zone of reception of the new low-frequency field D 1 ′ emitted by the first antenna B 1 , regardless of the power supply voltage of the first antenna B 1 , even if the latter is lower than the nominal voltage. In a preferential embodiment, the first and second antennas B 1 , B 2 are coaxial and wound around the same ferrite F′ (cf. FIG. 5 ).

The ferrite F′ makes it possible to increase the intensity of the low-frequency fields D 1 , D 2 , D 2 ′ emitted by the first and the second antennas B 1 , B 2 .

The second antenna B 2 is therefore then electromagnetically coupled to the first antenna B 1 and it emits, by resonance, the second and third radiofrequency fields D 2 , D 2 ′.

To this end, the second antenna B 2 is connected to means for adapting its frequency f′ to the frequency f of the first antenna B 1 .

The means M 1 for adapting the frequency f′ of the second antenna B 2 comprise, for example:

a second switch S 2 , connected on one side to a first end of the second antenna B 2 , and on the other side to a frequency adaptation circuit comprising:

an adaptation element, for example a capacitor C 2 linked to the switch S 2 , a third resistor R 3 linked on one side to the capacitor C 2 and on the other side to a second end of the second antenna B 2 .

When the second switch S 2 is closed, the second antenna B 2 is linked to the frequency adaptation circuit, that is to say connected in series, to the capacitor C 2 and to the resistor R 3 .

The value of the capacitor C 2 is determined in order to adjust the frequency f′ of the second antenna B 2 to the frequency f of the first antenna B 1 . Thus, the second antenna B 2 is a resonant antenna, which, when the second switch S 2 is closed and the first switch S 1 is connected to the first circuit, receives a part of the new low-frequency field D 1 ′ emitted by the first antenna B 1 and in turn emits a second and third low-frequency field D 2 , D 2 ′ at the same frequency f.

The resistor R 3 is optional, it is of low value in order not to limit the voltage circuiting through the second antenna B 2 and not to limit the range of the second and third low-frequency fields D 2 , D 2 ′.

Thus, the second and third low-frequency fields D 2 , D 2 ′ are of sufficient range to be received by the central unit 12 .

The operation of the wheel 11 electronic unit 13 according to the invention is described below.

In a first step, the first switch S 1 is in a first position in which it electrically links the voltage generator G to the first circuit (in which the resistor R 1 is of low value). The second switch S 2 is open, the second antenna B 2 is not operating. The first antenna B 1 emits a first low-frequency field D 1 oriented along the axis Y.

In a second transition step, the first switch is disconnected from the first circuit.

In a third step, the first switch S 1 is in a second position in which it electrically links the voltage generator G to the second circuit (in which there is a resistor R 2 of higher value than the resistor R 1 ). The second switch S 2 is then closed simultaneously, and the second antenna B 2 operates as a resonant antenna. The first antenna B 1 emits a new low-frequency field D 1 ′ oriented along the axis Y but of very short range. The second antenna B 2 receives the new low-frequency field B 1 ′ emitted by the first antenna B 1 and in turn emits, by resonance, a second and third low-frequency field D 2 , D 2 ′, both at right angles to the axis Y, to the central unit 12 at the same frequency f.

In a fourth transition step, the first switch S 1 is disconnected from the second circuit and the second switch S 2 is open.

The steps 1 to 4 are repeated continuously over a wheel revolution.

The first and the third steps are of predetermined durations, t 1 , t 2 , which can be equal to one another, for example 20 ms.

The method for transmitting low-frequency waves from the emitting unit 20 ′ to the wheel unit 13 according to the invention therefore comprises the following steps:

step 1: activation of the regulation means M 2 in order to power the first antenna B 1 with a nominal voltage for a first predetermined duration t 1 , step 2: deactivation of the regulation means M 2 , step 3: activation of the regulation means M 2 in order to power the first antenna B 1 with a voltage lower than the nominal voltage and activation of the adaptation means M 1 simultaneously for a second predetermined duration t 2 , step 4: deactivation of the regulation means M 2 and deactivation of the adaptation means M 1 simultaneously. step 5: repetition of steps 1 to 4.

In step 1, “activation of the regulation means” should be understood to mean the connection between the first switch S 1 and the first circuit of nominal voltage in order to power the first antenna B 1 with a nominal voltage.

In step 2, the deactivation of the regulation means that the first switch S 1 is no longer linked electrically to any circuit.

In step 3, the activation of the regulation means that the first switch S 1 is linked electrically to said second circuit, thus powering the first antenna B 1 with a voltage lower than the nominal voltage. It is accompanied by the simultaneous activation of the adaptation means M 1 which means the closure of the second switch S 2 , to connect the second antenna B 2 to the frequency adaptation circuit, comprising the capacitor C 2 and the resistor R 3 .

The activation and the deactivation of the regulation means and of the adaptation means are controlled by the control means M 3 incorporated in the microcontroller 20 ′.

Thus, the wheel unit 13 ′ according to the invention sequentially emits a first low-frequency field D 1 oriented along the axis Y, then a second and third low-frequency field D 2 , D 2 ′ at right angles to the axis Y.

FIG. 6 shows the reception pattern of the wheel unit 13 according to the invention, that is to say the intensity Rfi of the low-frequency LF signals received over a wheel revolution. The first field D 1 , emitted by the first antenna B 1 , exhibits a rupture zone Zo at 225°, the second field D 2 , emitted by the second antenna B 2 , exhibits a second rupture zone Zo 2 at 270°. The field formed by the joining of said two low-frequency fields D, D 2 does not exhibit any rupture zone over a wheel revolution. By alternating the emission of the low-frequency LF waves from the emitting unit 20 ′, by the first antenna B 1 , then by the second antenna B 2 , there is no longer any rupture zone over a wheel revolution.

Thus, the probability of reception of the low-frequency LF signals by the wheel unit 13 over a wheel revolution is increased. The rupture zone Zo is considerably reduced, even eliminated. Since the second antenna B 2 is passive, it is inexpensive, and also as it is oriented along the same axis Y as that of the first antenna B 1 , and not at right angles to said first antenna B 1 , the bulk of the emitting unit 20 ′ according to the invention is reduced.

The invention therefore allows for the reliable transmission of low-frequency LF signals between the emitting unit and the wheel unit over a complete wheel revolution, without the presence of any rupture zone.