FR3074402A1 - MASS LOOP SYSTEM INTEGRATING AN ELECTRIC COUPLING DEVICE ACTING ON A PARASITIC CURRENT - Google Patents

Abstract

A system (S) comprises two electrical equipments (EE1-EE2) each comprising an electric circuit (CE1, CE2) associated with a ground and an electric coupling device (DC). The masses associated with the electrical circuits (CE1, CE2) are coupled to each other by at least one electrical wire (BC) and to an element (EM1) defining a reference ground via a ground connection (LM) or at least one parasitic coupling (CP1, CP2), and the associated masses, the electric wire (BC), the element (EM1), each ground connection (LM) and / or each parasitic coupling (CPk) respectively constituting parts of a loop of mass in which circulates a parasitic current resonating with a resonant frequency. The electrical coupling device (DC) interconnects two parts of the ground loop to induce an offset of the resonant frequency and / or an attenuation of the parasitic current intensity.

Description

MASS LOOP SYSTEM INCLUDING AN ELECTRIC COUPLING DEVICE ACTING ON A SURFACE CURRENT

The invention relates to systems comprising electrical (or electronic) equipment comprising electrical circuits associated with masses participating in a ground loop.

Certain systems, such as for example certain vehicles (possibly motor vehicles), comprise at least two electrical (or electronic) pieces of equipment which each comprise at least one electrical circuit associated with ground. It will be noted that the latter may possibly be a ground plane forming part of the electrical circuit.

It often happens that the masses associated with the electrical circuits of this electrical equipment are coupled together by at least one electrical wire (possibly the shielding of an electrical cable shielding) and to at least one element which defines a reference ground via a link. mass or at least one parasitic coupling. It will be noted that the aforementioned electric wire may possibly consist of at least two subparties which extend mutually, for example at a splice.

In what follows, “parasitic coupling” means both a parasitic capacitance at low frequencies and an electromagnetic coupling at high frequencies.

It should be noted that the possible electric cable provided with a shielding can constitute, for example and without limitation, an LVDS interface (“Low Voltage Differential Signaling”), or Ethernet.

In the presence of the arrangement described above, the masses associated with the electrical circuits, the electric wire, the element defining a reference mass, each ground connection and / or each parasitic coupling may respectively constitute parts of a loop mass in which a parasitic current flows having a frequency which can enter into resonance with at least one frequency called resonance.

As those skilled in the art know, the circulation of this parasitic current in the ground loop generates radiation which induces electromagnetic disturbances which are penalizing for certain functions, such as for example the reception of radio waves.

The aforementioned resonant frequency can vary according to different parameters of the system considered, such as for example the lengths of the electric wire and the possible electrical ground connection, the geometrical layout of the electric wire and the possible electrical ground connection. , and the dimensions and impedance of the ground loop. Consequently, certain frequency bands (for example critical for the reception of radio waves) can be more or less impacted from one system to another or from one variation of a system to another variation of this same system.

This drawback is particularly annoying when it is difficult, if not impossible, to modify the environment of electrical equipment, and / or to move electrical equipment, and / or to change the length of the electrical wire and / or d '' an electrical ground connection, and / or modify an electronic card.

At least three solutions have been proposed to reduce the influence of the ground loop.

A first solution consists in installing outside electrical equipment, on existing electrical connections, filtering components such as for example ferrite cores (with inductive and resistive behavior), which allow the resonance frequency to be slightly shifted and reduce the amplitude of the stray current. However, this only induces resistive and resistive effects on the existing mass network, and therefore only allows limited modifications. In addition, the efficiency of this first solution is limited to a frequency band which is relatively narrow and depends on the characteristics of the ferrite core, and therefore when one is in the presence of several resonant frequencies one is forced to associate several ferrite cores with complementary characteristics to cover a wide frequency band. In addition, this first solution can sometimes prove to be difficult to integrate into a system due to the size of the ferrite core (s) and the method used for this integration.

A second solution consists in installing outside of the electrical equipment wired elements adapting the impedance according to their length, and often called "stubs". This makes it possible to offset each resonant frequency of the ground loop but without reducing the intensities of the stray currents due to the absence of electrical energy consumption. In addition, the length of the impedance matching wire depends on the architecture of the ground network and the resonant frequencies of the ground loop. In addition, the fact of acting on all the resonance frequencies simultaneously, without discrimination, can induce a simple transposition of the disturbance problem and therefore the appearance of new resonance frequencies in another frequency band. Furthermore, this second solution is mainly based on an electromagnetic effect which is sensitive to the environment of the impedance matching wire, which makes it very dependent on its environment, and in particular on the distance separating the wire. impedance matching of neighboring conductors, which frequently varies from one electrical architecture to another and from one system to another.

A third solution consists in installing electrical components inside the electrical equipment, resistive, inductive and / or capacitive. This makes it possible to offset each resonance frequency of the ground loop and to reduce the intensities of the stray currents, but this requires choosing the values of each of the electrical components added according to the electrical architecture of each system considered, which s 'proves difficult to achieve in practice as soon as the number of variants of electrical architecture becomes significant. In addition, these added electrical components modify the electrical behavior of the input / output interfaces of electrical equipment, which often leads to an unfavorable modification of other electrical performance or of electromagnetic compatibility.

The invention therefore aims in particular to improve the situation.

To this end, it proposes in particular a system comprising at least two electrical (or electronic) equipment items each comprising at least one electrical circuit associated with a ground, the masses associated with the electrical circuits being coupled together by at least one electric wire and one element. defining a reference mass via a ground link or at least one parasitic coupling, and the associated masses, the electric wire, the element, each ground link and / or each parasitic coupling respectively constituting parts of a ground loop in which a parasitic current circulating resonates with at least one resonant frequency.

This system is characterized by the fact that it also comprises at least one electrical coupling device interconnecting, via electrical connections, at least two parts of the ground loop in order to induce a shift in the resonant frequency in a band of selected frequencies and / or an attenuation of a stray current intensity for this resonant frequency.

Each electrical coupling device thus participates in the ground loop and therefore induces a modification of its characteristics which results in an offset in a chosen frequency band of the / each resonant frequency which it presents in its absence and / or by an attenuation of the intensity which the stray current exhibits in its absence for the / each resonant frequency.

The system according to the invention may include other characteristics which can be taken separately or in combination, and in particular:

- In a first embodiment, the (or at least one) electrical coupling device can interconnect, via electrical connections, at least the masses which are associated with the electrical equipment;

- It can also include another element defining a reference mass and coupled to one of the electrical equipment via parasitic couplings respectively. In this case, in a second embodiment, the (or at least one) electrical coupling device can interconnect, via electrical connections, at least this other element to ground which is associated with the electrical equipment which is coupled to this other element via parasitic coupling. Alternatively (third embodiment), the (or at least one) electrical coupling device can interconnect, via electrical connections, at least the two elements;

each electrical coupling device can comprise at least one linear electrical component and / or at least one non-linear electrical component;

> each linear electrical component can be chosen from a resistive component, an inductive component, and a capacitive component;

> each non-linear electrical component can be chosen from a varistor and a semiconductor component;

> the (or at least one) electrical coupling device may comprise at least two electrical components mounted in series and / or in parallel;

- at least one of the electrical circuits of the electrical equipment can be printed on an electronic card;

- it can constitute a vehicle, possibly a motor vehicle.

Other characteristics and advantages of the invention will appear on examining the detailed description below, and the attached drawings, in which:

FIG. 1 diagrammatically and functionally illustrates a first embodiment of a system according to the invention,

FIG. 2 diagrammatically and functionally illustrates a second embodiment of a system according to the invention, and

- Figure 3 illustrates schematically and functionally a third embodiment of a system according to the invention.

The object of the invention is in particular to propose a system S comprising at least two electrical (or electronic) items of equipment EEj comprising electrical circuits CEj associated with masses Mj participating in a ground loop inducing electromagnetic disturbances less troublesome than those of the prior art.

It is considered in what follows, by way of nonlimiting example, that the system S is a motor vehicle, such as for example a car. However, the invention is not limited to this type of system. It indeed relates to any system comprising electrical equipment comprising electrical circuits associated with masses participating in a ground loop. Consequently, it relates in particular to vehicles (land, sea (or river) or air), satellites, installations (possibly of industrial type), multifunction devices (possibly general public), and buildings.

There are schematically and functionally illustrated in Figures 1 to 3 three different embodiments of a system S according to the invention.

As illustrated, a system S, according to the invention, comprises at least two electrical (or electronic) equipment EEj, at least one first element EM1 defining a first reference mass, and at least one electrical coupling device DC.

In the three examples illustrated without limitation in FIGS. 1 to 3, the system S only comprises first EE1 (j = 1) and second EE2 (j = 2) electrical equipment EEj. But it could include more than two EEj electrical equipment. For example, when the system S is a motor vehicle, the first electrical equipment EE1 can be an electronic computer or a receiver of radio waves (possibly a car radio), and the second electrical equipment EE2 can be another electronic computer or a display screen or a sensor or even an actuator.

Furthermore, in the three examples illustrated without limitation in FIGS. 1 to 3, the system S comprises first EM1 and second EM2 elements respectively defining two reference masses. But it could include a single element defining a reference mass, or even more than two elements each defining a reference mass. For example, when the system S is a motor vehicle, the first EM1 and second EM2 elements can be two parts of the structure. Thus, the first element EM1 can, for example, be a part of the metal frame, and the second element EM2 can, for example, be the metal cross member which in particular supports the dashboard.

Each of the electrical equipment EEj comprises at least one electrical circuit CEj associated with a mass Mj.

For example, at least one of the electrical circuits CEj can be printed on an electronic card.

Also for example, the mass Mj associated with an electrical circuit CEj may be the mass of the electrical equipment EEj, for example defined on a metal part of its housing, or else, as illustrated, may be part of this electrical circuit CEj or any electronic card to which the latter belongs (CEj). In the latter case, the mass Mj may possibly be a ground plane.

The masses Mj which are associated with the electrical circuits CEj are coupled together by at least one electrical wire BC and by an element EM1 which defines a reference mass via a ground link LM or at least one parasitic coupling CPk.

It will be noted that the electrical wire BC can possibly consist of at least two sub-parts which extend mutually, for example at a splice.

The electric wire BC can be part of a shield of an electric cable CA coupling between them the electric circuits CEj, as illustrated without limitation in FIGS. 1 to 3, or else can be part of an unshielded electric cable and comprising possibly at least one other electrical wire for the transport of signals (possibly power).

The possible shielded AC electrical cable can constitute, for example and without limitation, an LVDS, Ethernet or A2B® interface. It depends on the functions provided by the EEj electrical equipment.

In the three examples illustrated without limitation in FIGS. 1 to 3, the system S comprises first EM1 and second EM2 elements, the first mass M1 is coupled to the first element EM1 via a ground link LM, and the second mass M2 is coupled to the second element EM2 via a parasitic coupling CP1. However, the first mass M1 could be coupled to the first element EM1 via a parasitic coupling and / or the second mass M2 could be coupled to the second element EM2 via another ground connection.

Each possible LM ground link can, for example, be an electric wire possibly fitted with an insulating sheath, or a small metal rod provided with screws. It will be noted that this electrical wire may possibly consist of at least two sub-parts which extend mutually, for example at a splice.

In the first example illustrated without limitation in FIG. 1, the second mass M2 is coupled to the second element EM2 via a first parasitic coupling CP1 (k = 1), and the second element EM2 is coupled to the first element EM1 via a second parasitic coupling CP2 (k = 2). Consequently, the second mass M2 is coupled to the first element EM1 via the first parasitic coupling CP1, the second element EM2 and the second parasitic coupling CP2. The second electrical equipment EE2 is therefore here "floating" (that is to say that its second mass M2 is not directly connected to that of an element EM1 or EM2).

In the second example illustrated without limitation in FIG. 2, the second mass M2 is coupled to the second element EM2 via an electrical coupling device DC to which we will return later, and the second element EM2 is coupled to the first element EM1 via a second parasitic coupling CP2 (k = 2). Consequently, the second mass M2 is coupled to the first element EM1 via the electrical coupling device DC, the second element EM2 and the second parasitic coupling CP2. Furthermore, there is also a third parasitic coupling CP3 between the first M1 and second M2 masses.

In the third example illustrated without limitation in FIG. 3, the second mass M2 is coupled to the second element EM2 via a first parasitic coupling CP1 (k = 1), and the second element EM2 is coupled to the first element EM1 via a coupling device electric DC. Consequently, the second mass M2 is coupled to the first element EM1 via the first parasitic coupling CP1, the second element EM2 and an electrical coupling device DC. The second electrical equipment EE2 is therefore floating here. Furthermore, there is also a third parasitic coupling CP3 between the first M1 and second M2 masses.

The masses Mj (associated respectively with the electrical circuits CEj), the electric wire BC, each element EM1, EM2, each possible ground connection LM and / or each parasitic coupling CPk respectively constitute parts of a ground loop in which a stray current entering into resonance with at least one resonant frequency.

Each DC electrical coupling device interconnects, via LEm electrical connections, at least two parts of the ground loop in order to induce a shift of the / each resonance frequency in a chosen frequency band and / or an attenuation of the intensity of the stray current for the / each resonant frequency. In other words, each DC electrical coupling device is a user of electrical current who participates in the ground loop in order to modify its characteristics and thus shift in / in a selected frequency band the / each resonant frequency which it presents in its absence and / or attenuate the intensity that the stray current exhibits in its absence for the / each resonant frequency.

The frequency offset is intended to protect as much as possible at least one frequency band to be protected. By way of example, a frequency band to be protected can be a band comprising a radio frequency which has been selected by the user of a radiocommunication receiver.

It will be understood that as a function of the needs, and more precisely of the frequency band (s) to be protected, the DC electrical coupling device (s) will:

- either only induce a shift in the (each) resonant frequency in a frequency band different from the frequency band (s) to be protected,

- either only induce a reduction in the intensity of the stray current so that the (each) resonant frequency does not disturb the frequency band (s) to be protected,

- either induce not only a shift of the (each) resonant frequency in a frequency band different from the frequency band (s) to be protected, but also an attenuation of the intensity of the stray current so that the ( each) resonant frequency does not disturb the frequency band (s) to be protected.

With each offset and / or each attenuation, the electromagnetic disturbances become minimal for each frequency band to be protected, and therefore the function which uses the latter is not, or almost not, penalized.

It will be noted that in the three examples illustrated without limitation in FIGS. 1 to 3, the system S only comprises a single DC electrical coupling device. But it could include several (at least two). Furthermore, in the three examples illustrated without limitation in Figures 1 to 3, the DC electrical coupling device interconnects two parts of the ground loop via two electrical connections LE1 (m = 1) and LE2 (m = 2). However, a DC electrical coupling device can interconnect M parts of the ground loop via M electrical connections LEm, with m = 1 to M and M> 2. Thus, it could, for example, interconnect three parts of the ground loop via three LEm electrical connections.

It is important to note that in Figures 1 to 3, the DC electrical coupling device and the two electrical connections LE1 and LE2 vary, a priori, from one system to another.

Each LEm electrical connection can be an electrical wire or cable, optionally provided with an insulating sheath, or a welded or screwed metal rod.

As mentioned above, a DC electrical coupling device can provide at least three different interconnections.

Thus, the electrical coupling device DC can interconnect, via electrical connections LEm, at least the masses Mj which are associated with the electrical equipment EEj, as illustrated in FIG. 1. Here, the electrical coupling device DC interconnects, via two connections LE1 and LE2, the first M1 and second M2 masses which are respectively associated with the first EE1 and second EE2 electrical equipment.

In a first variant, the electrical coupling device DC can interconnect, via electrical connections LEm, at least the second element EM2 to the second ground M2 which is associated with the second electrical equipment EE2 (which is here coupled to the second element EM2 via the first parasitic coupling CP1, and therefore is not connected to the ground link LM), as illustrated in FIG. 2.

In a second variant, the electrical coupling device DC can interconnect, via electrical connections LEm, at least the first EM1 and second EM2 elements, as illustrated in FIG. 3.

It will be noted that each DC electrical coupling device can comprise at least one linear electrical component and / or at least one non-linear electrical component. In other words, each DC electrical coupling device can include one or more electrical components. When a DC electrical coupling device comprises at least two electrical components, these can be connected in series and / or in parallel.

It will also be noted that a DC electrical coupling device can possibly be distributed (or distributed) into at least two parts interconnecting possibly different parts of the ground loop.

Each linear electrical component can, for example, be chosen from a resistive component, an inductive component, and a capacitive component. Generally speaking, it is an impedance.

Each non-linear electrical component can, for example, be chosen from a varistor and a semiconductor component (such as a diode for example). However, non-linearity could result from frequency behavior or hysteresis (as in the case of a ferrite core).

As examples, a DC electrical coupling device can include:

- resistance or varistor,

- a resistor connected in series with a capacitor to form an RC circuit,

- a resistor connected in series with an inductor to form an RL circuit,

- a capacitor mounted in parallel with an inductor to form an LC circuit,

- two diodes mounted head to tail,

- a varistor connected in series with a capacitor,

- a varistor mounted in parallel with an inductor.

It will be understood that the choice and the characteristics of the electrical (or electronic) components of a DC electrical coupling device are made as a function of the desired frequency offset and / or of the desired intensity attenuation, and therefore as a function of the system S considered.

The invention offers several advantages, including:

- it does not require modification of the electrical equipment because each electrical coupling device is external to the latter, which allows its use in very many different electrical architecture systems,

- it acts on the electrical behavior and not on the electromagnetic behavior, which makes it much less sensitive to the proximity of other conductors of the system whose distances can vary notably from one electrical architecture to another,

- it makes it possible to act when necessary both on the resonant frequencies and on the intensities of the stray currents,

- it allows selectivity in the resonance frequencies to be shifted,

- it does not need to rely on the existing mass network, which offers more possibilities for integration and adaptation.

Claims (10)

1. System comprising at least two electrical items of equipment (EEj) each comprising at least one electrical circuit (CEj) associated with a mass (Mj), said masses (Mj) associated with said electrical circuits (CEj) being coupled together by at least one electric wire (BC) and to an element (EM1) defining a reference mass via a ground link (LM) or at least a parasitic coupling (CPk), and said associated masses, said electric wire (BC), said element ( EM1), each ground link (LM) and / or each parasitic coupling (CPk) respectively constituting parts of a ground loop in which circulates a parasitic current entering into resonance with at least one resonant frequency, characterized in that '' it further comprises at least one electrical coupling device (DC) interconnecting via electrical links (LEm) at least two parts of said ground loop in order to induce an offset of said resonant frequency e in a selected frequency band and / or an attenuation of an intensity of said stray current for said resonant frequency. 2. System according to claim 1, characterized in that said electrical coupling device (DC) interconnects, via electrical connections (LEm), at least said masses (Mj) associated with said electrical equipment (EEj). 3. System according to claim 1, characterized in that it comprises another element (EM2) defining a reference mass and coupled to said element (EM1) and to one of said electrical equipment (EE2) via parasitic couplings respectively ( CPk), and in that said electrical coupling device (DC) interconnects, via electrical connections (LEm), at least said other element (EM2) to said ground (M2) associated with said electrical equipment (EE2) which is coupled to said other element (EM2) via parasitic coupling (CPk). 4. System according to claim 1, characterized in that it comprises another element (EM2) defining a reference mass and coupled to said element (EM1) and to one of said electrical equipment (EE2) via parasitic couplings respectively ( CPk), and in that said electrical coupling device (DC) interconnects, via electrical links (LEm), at least said element (EM1) to said other element (EM2). 5. System according to one of claims 1 to 4, characterized in that said electrical coupling device (DC) comprises at least one linear electrical component and / or at least one non-linear electrical component. 6. System according to claim 5, characterized in that each linear electrical component is chosen from a resistive component, an inductive component, and a capacitive component. 7. System according to claim 5 or 6, characterized in that each non-linear electrical component is chosen from a varistor and a semiconductor component. 8. System according to one of claims 5 to 7, characterized in that said electrical coupling device (DC) comprises at least two electrical components connected in series and / or in parallel. 9. System according to one of claims 1 to 8, characterized in that at least one of said electrical circuits (CEj) is printed on an electronic card. 10. System according to one of claims 1 to 9, characterized in that it constitutes a vehicle.