Method for diagnosing a communication link in a motor vehicle
A method for diagnosing the status of a communication link between an interior relay antenna and an exterior relay antenna of a motor vehicle. The method includes measuring a first voltage value defined between the midpoint of the electrical circuit and the second ground when the switch is in the open position, measuring a second voltage value defined between the midpoint of the electrical circuit and the second ground when the switch is in the closed position, calculating the value of the variable resistor from the first measured voltage value, from the second measured voltage value, from the value of the voltage defined across the terminals of the voltage source and from the values of the first resistor and of the second resistor, and diagnosing the status of the communication link on the basis of the calculated value of the variable resistor.
1. A method for diagnosing a status of a communication link between an interior relay antenna mounted in the passenger compartment of a motor vehicle and an exterior relay antenna mounted on a body of said motor vehicle, the status of said communication link being determined by a value of a voltage defined across terminals of a variable resistor that is connected both to an intermediate point of the communication link, located between the interior relay antenna and the exterior relay antenna, and to a first ground, said method being implemented by a diagnostic module comprising an electrical circuit including a midpoint that is connected to the interior relay antenna, a first resistor that is connected both to a voltage source and to said midpoint, and a capacitor that is connected both to the midpoint and to a second ground that is different from the first ground, the diagnostic module further comprising a second resistor that is linked to the midpoint of the electrical circuit and connected in series with a switch linked to the voltage source, the method comprising:
measuring a first voltage value defined between the midpoint of the electrical circuit and the second ground when the switch is in the open position;
measuring a second voltage value defined between the midpoint of the electrical circuit and the second ground when the switch is in a closed position;
calculating a value of the variable resistor from the first measured voltage value, from the second measured voltage value, from the value of a voltage defined across terminals of the voltage source and from the values of the first resistor and of the second resistor; and
diagnosing the status of the communication link on the basis of the calculated value of the variable resistor.
2. The method as claimed in claim 1 , wherein the value of the variable resistor is calculated by solving a system of equations with two unknowns, which are the value of the voltage defined across the terminals of the variable resistor and the value of the difference in voltage between the first ground and the second ground according to the following equations:
V
1
=
V
CC
×
RV
R
1
+
RV
+
(
M
1
-
M
2
)
V
2
=
V
CC
×
RV
R
1
×
R
2
R
1
+
R
2
+
RV
+
(
M
1
-
M
2
)
(
I
)
where:
RV is the value of the variable resistor,
Vcc is voltage of the voltage source,
V 1 is the first voltage value defined between the midpoint of the electrical circuit and the second ground M 2 ,
V 2 is the second voltage value defined between the midpoint of the electrical circuit and the second ground M 2 ,
R 1 is the value of the first resistor,
R 2 is the value of the second resistor,
M 1 is the first ground, and
M 2 is the second ground.
3. A diagnostic module configured to be mounted in a motor vehicle so as to diagnose a status of a communication link between an interior relay antenna mounted in the passenger compartment of said motor vehicle and an exterior relay antenna mounted on the body of said motor vehicle, the status of said communication link being determined by the value of a voltage defined across terminals of a variable resistor that is connected both to an intermediate point of the communication link, located between the interior relay antenna and the exterior relay antenna, and to a first ground, the diagnostic module comprising:
an electrical circuit including a midpoint that is configured to be linked to the interior relay antenna, a first resistor that is connected both to a voltage source and said midpoint, and a capacitor that is connected both to the midpoint and to a second ground that is different from the first ground;
an analog-to-digital converter, an input of which is connected to the midpoint of the electrical circuit; and
a microcontroller, an input of which is connected to an output of the analog-to-digital converter so as to receive a digital value corresponding to an analog voltage measured between the midpoint and the second ground,
a second resistor that is linked to the midpoint of the electrical circuit and connected in series with a switch linked to the voltage source; and
means for switching the switch between an open position and a closed position,
and wherein the microcontroller is configured to calculate the value of the variable resistor from a first digital value received from the analog-to-digital converter when the switch is in the open state, from a second digital value received from the analog-to-digital converter when the switch is in the closed state, from the value of the voltage defined across terminals of the voltage source and from the values of the first resistor and of the second resistor in order to diagnose the status of the communication link.
4. The diagnostic module as claimed in claim 3 , wherein the microcontroller is configured to calculate the value of the variable resistor by solving a system of equations with two unknowns, which are the value of the voltage defined across the terminals of the variable resistor and the value of the difference in voltage between the first ground and the second ground according to the following equations:
V
1
=
V
CC
×
RV
R
1
+
RV
+
(
M
1
-
M
2
)
V
2
=
V
CC
×
RV
R
1
×
R
2
R
1
+
R
2
+
RV
+
(
M
1
-
M
2
)
(
I
)
where:
RV is the value of the variable resistor,
Vcc is voltage of the voltage source,
V 1 is the first voltage value defined between the midpoint of the electrical circuit and the second ground M 2 ,
V 2 is the second voltage value defined between the midpoint of the electrical circuit and the second ground M 2 ,
R 1 is the value of the first resistor,
R 2 is the value of the second resistor,
M 1 is the first ground, and
M 2 is the second ground.
5. The diagnostic module as claimed in claim 3 , wherein the switch comprises a MOSFET transistor.
6. The diagnostic module as claimed in claim 5 , wherein the switch comprises two Zener diodes that are connected via a common cathode, and the anodes of which are connected to a source and to a gate, respectively, of the transistor.
7. The diagnostic module as claimed in claim 5 , wherein the switch comprises a diode, the anode of which is connected to a drain of a transistor and the cathode of which is connected to the source of the transistor.
8. The diagnostic module as claimed in claim 5 , wherein the means for switching the switch comprise an AC voltage source that is connected between a source and a drain of the transistor.
9. The diagnostic module as claimed in claim 3 , wherein the values of the first resistor and of the second resistor, and a maximum value of the variable resistor, are equal.
10. A motor vehicle comprising:
an interior relay antenna mounted in a passenger compartment of said motor vehicle;
an exterior relay antenna mounted on a body of said motor vehicle;
a communication link linking said interior relay antenna and said exterior relay antenna;
a variable resistor that is connected both to an intermediate point of a communication link, located between the interior relay antenna and the exterior relay antenna, and to a first ground, and a value of a voltage of which, defined across its terminals, allows a status of said communication link to be determined; and
the diagnostic module as claimed in claim 3 , the midpoint of which is linked to the interior relay antenna.
11. The diagnostic module as claimed in claim 4 , wherein the switch comprises a MOSFET transistor.
12. The diagnostic module as claimed in claim 6 , wherein the switch comprises a diode, the anode of which is connected to the drain of the transistor and the cathode of which is connected to the source of the transistor.