EP2223320B1 - Circuit for a contact relay - Google Patents

Abstract

The invention relates to an electrical circuit comprising a power supply (Vsupply), a control means (3, 30) and a relay (1, 10) comprising a coil (2, 20) supplied by said power supply, the control means (3, 30) being capable of causing a contact of the relay to switch from a first position to a second position, characterized in that it includes current flow means capable of making a current flow through the contact in the first position, between the start of the controlling of the switching of the contact between a first position and a second position and its effective switch-over into the second position.

Description

The invention relates to the field of electromagnetic relays and aims in particular a circuit for relays used in motor vehicles.

A relay is an electrical device in which an electrical phenomenon (current or voltage) controls the On / Off switching of a mechanical element (electromechanical relay) or an electronic element (static relay), which acts as a switch that the we can operate from a distance. In an inverting relay, the current flowing in a rest or working contact may be insufficient to allow satisfactory cleaning of this contact. The relay can then clog up as and when there is no current flowing when the change of position of the mechanical element is requested.

To have a sufficient current in the resting contact or the working contact capable of allowing a satisfactory cleaning of this contact, one solution is to add a load resistance on the line between the rest point and the ground to reach the necessary current, called cleaning stream. Thus when the switchover command is requested, the current can flow directly into the load. But this solution leads to permanently dissipate a significant power in the resistance. Other solutions consisting of adding a network of resistor (s), capacitor (s), diode (s) or else using contact relays under vacuum or with mercury contact make it possible to avoid fouling of the resting contact. . However, these solutions are very expensive. In addition the use of mercury is being banned, and the use of a vacuum contact relay is limited in switching power.

The document WO96 / 41358 describes a device according to the preamble of claim 1.

An object of the present invention is to provide an improved circuit, simple and inexpensive, which allows the current to flow in the contact in a first position during the time between the start of the relay control and the effective switching of the contact in a second position and proceed thus to cleaning the contact.

For this purpose, the object of the invention is a circuit for contact relays comprising a power supply source, a control means, a relay comprising a coil supplied by said power supply source, the control means being adapted to control the switching of a contact of the relay from a first position to a second position, characterized in that it comprises means for circulating current capable of circulating a current in the contact in the first position, between the start of switching control of the contact between a first and a second position and its effective changeover in the second position.

• les moyens pour la circulation de courant peuvent être disposés en aval du contact de la première position et en amont de la commande relativement au sens de circulation du courant,
• les moyens pour la circulation de courant peuvent comporter une résistance en série avec une diode, une borne de ladite résistance étant disposée en aval du contact de la première position, l'autre borne de la résistance étant reliée à l'anode de la diode,
• la cathode de la diode peut être reliée à un point du circuit formant un noeud disposé en aval de la bobine et en amont de la commande relativement au sens de circulation du courant, le contact dans la première position étant le contact repos,
• un moyen inverseur peut être disposé entre la cathode de la diode et le point formant un noeud disposé en aval de la bobine et en amont de la commande relativement au sens de circulation du courant, le contact dans la première position étant le contact travail,
• la valeur de la résistance peut être telle que l'intensité du courant est sensiblement supérieure à l'intensité du courant circulant dans le contact de la première position,
• la résistance peut être un élément résistif à coefficient de température positif,
• le moyen inverseur peut être un transistor de faible puissance.

According to other characteristics,

• the means for the flow of current can be arranged downstream of the contact of the first position and upstream of the control relative to the flow direction of the current,
• the means for the current flow can comprise a resistor in series with a diode, a terminal of said resistor being disposed downstream of the contact of the first position, the other terminal of the resistor being connected to the anode of the diode,
• the cathode of the diode can be connected to a point of the circuit forming a node disposed downstream of the coil and upstream of the control relative to the flow direction of the current, the contact in the first position being the resting contact,
• an inverter means may be arranged between the cathode of the diode and the point forming a node disposed downstream of the coil and upstream of the control relative to the flow direction of the current, the contact in the first position being the working contact,
• the value of the resistance may be such that the intensity of the current is substantially greater than the intensity of the current flowing in the contact of the first position,
• the resistor can be a resistive element with a positive temperature coefficient,
• the inverter means may be a low power transistor.

• la figure 1 représente le schéma d'un circuit selon l'invention pour un contact dans une première position repos,
• la figure 2 représente le schéma d'un circuit selon l'invention pour un contact dans une première position travail.

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings, given by way of non-limiting examples and in which:

• the figure 1 represents the diagram of a circuit according to the invention for a contact in a first rest position,
• the figure 2 represents the diagram of a circuit according to the invention for a contact in a first work position.

To the figure 1 there is shown a circuit for preventing clogging of the idle contact, comprising an electromagnetic relay 1 for example with inverter contacts, powered by a power supply source.

The relay 1 has a coil 2 energized by a power source V _lim or battery provided for controlling a contact.

A command 3 makes it possible to control the beginning of the control of the relay to effect the switching from a first position to a second position. As shown, the contacts of the relay 1 can from a common point C, establish a contact R when the relay is at rest, then establish another contact T when the relay is at work.

In the remainder of the description, the flow direction of the current is represented by the arrows 7.

To the figure 1 , the control 3 is a MOSFET transistor, which makes it possible to control the start of the control of the relay in order to switch the first rest position R to the second work position T.

The coil 2 of the relay 1 powered by the power source is connected to the control 3. When the command 3 is triggered, the coil 2 is energized, and the voltage applied to the coil 2 creates a current. This current produces an electromagnetic field at the end of the coil 2 which acts as an electromagnet. The magnetic field created when it is sufficient can then effectively switch the contact from the rest position R to the working position T.

Means capable of circulating the current in the rest contact R during the time between the start of the control 3 of the relay 1 and the actual switching to the working contact T are arranged between the rest contact R and the coil 2.

The means comprise a resistor 5 placed in series with a diode 6 on a circuit portion disposed between the contact in the first rest position R and the coil 2.

A terminal of the resistor 5 is disposed downstream of the resting contact R relative to the flow direction of the current, the other terminal of the resistor 5 being connected to the anode of the diode 6. The cathode of the diode 6 is connected to a point of the circuit forming a node disposed downstream of the coil 2 and upstream of the control 3, relative to the direction of flow of the current. The node is disposed upstream of the drain of the transistor relative to the flow direction of the current.

est sensiblement supérieure à l'intensité du courant I_{contact_première_position} circulant dans le contact de la première position repos nécessaire pour nettoyer le contact, où V _{a limmin} représente la tension d'alimentation minimum du circuit.The value R _cleaning of the resistor 5 is such that the intensity of the current $\frac{V_{\mathrm{at}{\lim }_{\min }}}{R_{\mathit{cleaning}}}$

is substantially greater than the intensity of the current I flowing in the _{contact_première_position} contact with the first rest position necessary to clean the contact, where V _{lim min} represents the minimum supply voltage of the circuit.

The minimum cleaning current allowing the contacts not to become dirty is, for example, substantially 40 mA for relays used in a motor vehicle.

For example, for a supply voltage of substantially 12V, a switchover delay of the contact of a duration of substantially 20ms, a switching frequency of substantially 1HZ, and for a current flowing in the contact rest substantially 150 mA, the power dissipated is 5.5mW while the dissipated power would be 900mW with a simple load resistance. The resting contact does not become clogged and the dissipated power is minimum.

Once the command 3 is triggered, current flows instantaneously in the resistor 5 and the current in the coil 2 increases. The contact which was in a first position, switches as soon as the current in the coil 2 reaches a threshold value sufficient for the effective switching of the working contact T. Thus, when switching the relay from the rest position R to the working position T, there is substantially no current flowing in the resistor 5 while the current was sufficient at the moment of switching.

The diode 6 advantageously avoids current recirculation phenomena especially during intermediate switching phases.

The resistor 5 and the diode 6 thus make it possible to pass current into the rest contact R during the time separating the start of the relay control and the actual switching of the working contact T.

According to another embodiment not shown, the resistor 5 is a positive temperature coefficient resistive element such as a thermistor similar to that used for the protection of electric motors against an excessive rise in temperature, made for example based on barium titanate, or type "resettable fuse" made of polymer material. When the relay does not switch, that is to say if it is faulty or if there is a connection fault of the relay control, and if the cleaning current is important, for example substantially 100 mA approximately, the resistive element will heat up, its resistance increases, and therefore limit the power dissipated by the circuit. Such a resistive element makes it possible not to dissipate a significant power permanently. This resistive element provides protection against the risk of destruction of circuits in case of failure of the relay or its connection.

To the figure 2 , there is shown a circuit for preventing fouling of the working contact T, comprising an electromagnetic relay 10 for example with inverter contacts, powered by a power supply source.

The relay 10 has a coil 20 supplied directly by a power supply V _{a lim} or battery provided for the control of a contact. A control 30, such as a MOSFET transistor, makes it possible to control the start of the control of the relay in order to switch from a first working position T to a second rest position R. The coil 20 of the relay 10 powered by the source supply is connected to control 30. As figure 1 when the magnetic field created by the coil 20 is sufficiently weak, the contact can switch from the working position T to the rest position R.

Means capable of circulating the current in the working contact T during the time between the start of the relay control and the actual switching of the rest contact R are placed between the work contact T and the coil 20.

A resistor 50 is placed in series with a diode 60 on a circuit portion disposed between the working contact T and the coil 20. A terminal of the resistor 50 is disposed downstream of the working contact T relative to the direction of flow of the current. another terminal of the resistor 5 being connected to the anode of the diode 60.

The inverter means 40, such as a low power MOSFET transistor, is disposed between the cathode of the diode 60 and a point forming a node, disposed downstream of the coil 20 and upstream of the control 30 relative to the direction of circulation. current so that the current flowing in the resistor can be synchronized with the opening of the contact to be cleaned. The cathode of the diode 60 is connected to the drain of the transistor 40. The source of the transistor 40 is connected to a point of the circuit forming a node disposed downstream of the coil 20 and upstream of the control 30 relative to the flow direction of the current. This node is disposed upstream of the drain of the transistor 30 relative to the flow direction of the current.

The value of the resistor 50 is such that the intensity of the current is substantially greater than the intensity of the current I _{contact_première_position} flowing in the contact first working position necessary to clean the contact, the duration of the changeover being dependent on the conditions of demagnetization of the coil 20 of relay 10.

When switching the relay from the first work position T to the second rest position R, there is substantially no current flowing in the resistor 50 when there was enough at the time of switching.

The work contact does not get dirty and the dissipated power is minimum.

In another embodiment not shown, the circuit comprises both the means able to circulate the current in the rest contact R during the time between the start of the relay control and the actual switching of the working contact T, and the means capable of circulating the current in the work contact T during the time between the start of the relay control and the actual switching of the rest contact R. Such a circuit advantageously allows to prevent the rest contact and the work contact s' fouling depending on the position of the relay at the time of ordering. A sufficient cleaning current is able to flow when relay control in the corresponding contact.

It will be understood that the controls 3.30, and the inverter means 40 are given as non-limiting examples. Any other type of control whose switching times are sufficiently short of the order of 10 to 40 ms, with respect to the relay switching time, that is to say to support the extra current related to the resistance during the switching time of the relay, can be used. The controls 3.30 and the inverter means 40 may for example be a bipolar transistor or a SMART or other type circuit.

Such a circuit, simple to carry out, and inexpensive, makes it possible to pass the current in the resting contact R during the time separating the start of the control of the relay and the actual switching of the working contact T or in the working contact T during the time separating the start of the relay control and the actual switching of the R rest contact.

The cleaning current is sufficient and prevents clogging of the relay contacts and the dissipated power is minimum.

Claims (8)

1. Circuit for a contact relay comprising

   a. an electric power source (V _{a lim})

   b. a control means (3, 30)

   c. a relay (1, 10) comprising a coil (2, 20) powered by said electric power source, the control means (3, 30) being suitable for controlling the switching of a contact of said relay from a first position to a second position,

   characterized in that it comprises current circulation means suitable for circulating a current in the contact in the first position, between the start of control of the switching of the contact between a first and a second position and its actual switchover to the second position.
2. Circuit according to Claim 1, characterized in that the current circulation means are positioned downstream of the contact of the first position and upstream of the control (3, 30) relative to the current circulation direction.
3. Circuit according to Claim 1 or 2, characterized in that the current circulation means comprise a resistor (5) in series with a diode (6), a terminal of said resistor (5) being positioned downstream of the contact of the first position, the other terminal of the resistor being linked to the anode of the diode (6).
4. Circuit according to Claim 3, characterized in that the cathode of the diode (6) is linked to a point of the circuit forming a node positioned downstream of the coil (2) and upstream of the control (3) relative to the current circulation direction, the contact in the first position being the normally closed contact.
5. Circuit according to Claim 3, characterized in that a reversing means (40) is positioned between the cathode of the diode (60) and the point forming a node positioned downstream of the coil (20) and upstream of the control (30) relative to the current circulation direction, the contact in the first position being the normally open contact.
6. Circuit according to one of Claims 2 to 5, characterized in that the value of the resistor R_cleaning (5, 50) is such that the intensity of the current $\frac{V_{a{\lim }_{\min }}}{R_{\mathit{cleaning}}}$

   

   is substantially greater than the intensity of the current circulating in the contact of the first position I_{contact_first_position} , in which V _{a limmin} represents the minimum power supply voltage of the circuit.
7. Circuit according to one of Claims 3 to 6, characterized in that the resistor (5) is a positive temperature coefficient resistive element.
8. Circuit according to one of Claims 5 to 7, characterized in that the reversing means (40) is a low power transistor.

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