FR2966642A1 - Electromechanical relay e.g. monostable electromechanical relay, for use in engine servo unit for automobile, has control circuit with current adjusting unit for adjusting current passing through electromagnet - Google Patents

Abstract

The relay has an electromagnet that is controlled by a control circuit i.e. micro controller (11), where the electromagnet is formed of a coil (13). The electromagnet transmits force to a switching circuit i.e. switch (12), when the electromagnet is supplied with power for assuring the output switching of a power circuit. The control circuit includes a current adjusting unit for adjusting the current passing through the electromagnet. A current measuring unit i.e. shunt resistor (22), measures the current passing through the electromagnet. An independent claim is also included for a method for switching an electromechanical relay.

Description

TECHNICAL FIELD The present invention relates generally to an electromechanical relay for switching electrical connections and more particularly to the control device of the electromagnet or coil of such a device. relay. These relays are used in particular in vehicle switching systems. TECHNOLOGICAL BACKGROUND 10 The electrical architectures of vehicles integrate more and more functions so that the electronic modules integrating these functions must manage and concentrate more and more power in a more and more limited volume. It emerges that some electronic boxes, in particular under the bonnet, have reached their technological and thermal limit. An example of a standard electromechanical relay structure contained in such housings is provided in FIG. 1. A microcontroller or control circuit 1 makes it possible to control the activation of a switch 2 through an electromagnet typically formed of a coil 3 wound around a magnetic circuit. In the context of an application in the field of the automobile, the source of energy comes from the battery 4 of the vehicle. With such a structure, it will be noted that the control of the coils is carried out continuously without servocontrol. -2

Such a standard structure has a number of disadvantages. Thus, in a vehicle, the battery coupled to the alternator can deliver a wide range of supply voltage (typically 5.6V to 18V). Some relays must be functional throughout this range. However, from a functional point of view, it is difficult to control or maintain the control of a high temperature relay during low voltage phases of the battery, such as at startup or in case of battery under charge. High battery voltage can cause damage to the relay, such as a rise in temperature, which can deteriorate. Moreover, from an energy consumption point of view, it is necessary to reduce more and more CO2 emissions from the vehicle, in particular to comply with current and future legislation in this area. If recent studies on the subject are taken into account, (TCS 2010 Consumer Catalog, page 4, http://www.bfe.admin.ch/energieetikette/00886/index.html?lang=en), one liter of diesel fuel is produced with a production of 2.61 Kg of CO2, which amounts to a consumption per I / 100km for a production of 26.1g CO2 / km. In addition another study (www.elsevier.com) shows that the consumption of 100 W of power requires 0.151 on 100km. It is therefore important to limit the dissipated power as much as possible. However the power dissipated by a standard relay can be quickly significant. Indeed, the contact of the relay is bonded through the magnetic field created by the current flowing in the coil. This current is dependent on the battery level and the resistance value of the coil which itself depends on the ambient temperature. Considering, for example, a maximum battery voltage (Ubat) in nominal operation of 16V and a coil resistance (Rbob) of the automotive standard electromagnet of 1200, the power dissipated in the coil is given by the formula next: Pbob = Ubat2 / Rbob = 162/120 = 2.13W -3

Without regulation, the current can vary by a factor greater than 3 because of the wide voltage range and the car temperature. However, the power dissipated by the relay is directly related to the current flowing through the coil and can reach a level too important for the component (relay) as for the product (calculator). It is therefore understood that a standard relay structure has deficiencies in terms of quality and safety in the diagnosis and detection of failure of relay coils to the extent that prevention means are not provided. aggravated warm-ups. Indeed, this dissipated power can be one of the main causes of heating of the product may cause thermal runaway and failures with impact on the operation and safety of the vehicle. SUMMARY OF THE INVENTION An object of the present invention is to overcome the drawbacks mentioned above by providing an electromagnetic relay coil control structure whose power dissipation is limited so as to minimize the risk of overheating and failures. while reducing energy consumption. For this purpose, a first aspect of the present invention relates to an electromechanical relay comprising an electromagnet controlled at the input by a control circuit and able to transmit when energized, a force to a switching circuit for switching output. of a power circuit, characterized in that the control circuit comprises means for regulating the current flowing through the electromagnet. The introduction of regulating means makes it possible to reduce the current flowing through the coil of the electromagnet and thus to improve the performance, in particular in terms of consumption by limiting the current consumed by the relay. The application of this principle to all relays of a

vehicle allows to multiply the effects obtained and to lower the global CO2 emission by the vehicle and thus to limit the penalties to the manufacturers. Such a relay structure with current regulation through the coil also improves the quality and safety by preventing aggravated heating. Finally, it allows a simplification of the design of the module under the engine hood due to less constraints on the choice of components due to the overall decline in temperature of the product. According to an advantageous embodiment, the regulation means are switching control means made by controlling the average current flowing through the electromagnet to a setpoint current by means of pulse width modulation control. Such regulation means have many advantages including functional by controlling or maintaining the control of the relays during low voltage phases of the battery, e.g. at startup, or for a battery under load ... This solution also improves the input of regulators (pre-regulation) of the product during low voltage phases; in accordance with the principle of switching power supplies using relay coils as inductors.

According to another advantageous embodiment, means are provided for measuring the current flowing through the electromagnet and regulating means which adjust the duty cycle of the pulse width modulation control as a function of the reference current and the current. current measurement.

According to another advantageous embodiment, a control signal of the electromagnet comprises a first switching phase, a second holding phase during which the pulse width modulation control is applied and a third release phase.

According to another advantageous embodiment, there is provided means for slow demagnetization of the electromagnet during the second holding phase in order to maintain a stable current. According to another advantageous embodiment, the slow demagnetization means consist of a diode connected in parallel with the electromagnet during the holding phase. According to another advantageous embodiment, there are provided means for rapid demagnetization of the electromagnet during the third release phase so as not to damage the contact by a slow opening. According to another advantageous embodiment, the rapid demagnetization means are constituted by a Zener diode connected in parallel with the electromagnet during the release phase. According to another advantageous embodiment, the frequency of pulse width modulation control is selected to be substantially less than the switching frequency of the control circuit. According to another advantageous embodiment, the frequency of the pulse width modulation control is selected to be higher than the audible frequencies for the animals. According to another advantageous embodiment, the electromechanical relay is a monostable electromechanical relay designed for the automobile. The invention according to a second aspect relates to a motor vehicle service unit comprising a plurality of electromechanical relays according to the first aspect. The invention according to a third aspect relates to a method of switching an electromechanical relay of a motor vehicle service unit comprising the steps of (i) controlling an electromagnet (13) input by a control circuit

(11), (ii) regulating by servocontrolling the average current (Ibob) passing through the solenoid to a setpoint current through a pulse width modulation control, (iii) transmitting a force to a control circuit. switching (12), and (iv) switching a power circuit output, BRIEF DESCRIPTION OF THE FIGURES Other features and advantages of the present invention will become more apparent upon reading the following detailed description of embodiments of the present invention. invention given by way of non-limiting examples and illustrated by the accompanying drawings, in which: - Figure 1, already described, shows a standard electromechanical relay structure; Figure 2 shows an electromechanical relay structure according to an embodiment of the present invention; FIG. 3 represents an activation timing diagram of a relay according to one embodiment of the present invention; - Figure 4 shows schematically the servo structure of an electromechanical relay; Figure 5 shows the current curve passing through the relay; FIG. 6 represents the evolution of the switching losses with respect to the control signal. DETAILED DESCRIPTION OF THE INVENTION The invention will be described hereinafter solely by way of non-limiting examples in relation to FIGS. 2 to 6. The calculation assumptions will be given for information only to illustrate the invention. As mentioned in the introduction, one of the main objectives of the present invention is to limit the power dissipated by the electromechanical components, for example of the monostable relay type, switching power supplies for the bodies of a vehicle. This dissipated power can be one of the main causes of heating of the product which can cause thermal runaway and failure with impact on the operation and safety of the vehicle. FIG. 2 shows an electromechanical relay structure according to a preferred embodiment of the present invention in which the power limitation is achieved by relay coil control in PWM mode, i.e. Width Modulation. pulse, with a servo of the average current flowing through the relay coil. In FIG. 2, there is a microcontroller or control circuit 11 making it possible to control the activation of a switch 12 to ensure the output switching of a power circuit (not shown) through an electromagnet formed typically a coil 13 wound around a magnetic circuit. The switch 12 or relay contact is bonded through the magnetic field created by the current flowing in the coil 13. In the context of an application in the field of the automobile, the energy source comes from the battery 14 of the vehicle. A control stage 15 is placed at the output of the control circuit 11 to ensure the transmission of a setpoint to the rest of the relay. This control stage 15 comprises an adaptation resistor and a control transistor 16. In PWM mode, an RC filter 17 filters the pulse width modulated signal, storing a DC component across the capacitor C and controlling the current. output a switch, for example a transistor 18 of the NPN type. Transistor 18 in turn controls another switch, a PNP transistor 19 in this example.

So that the equivalent circuit of the relay structure is to have the diodes 20 and 23 in parallel with the coil 13. The diodes 20 and 23 are maintained in parallel with the coil 13 as the transistor 19 remains conductive. Thus, when the pulse width modulation signal is in the low state, the relay structure allows slow demagnetization through the diodes 20 and 23 (slope = Vdiode / L). When the pulse width modulation signal is high, the relay structure magnetizes the coil through transistor 16. When the pulse width modulation signal remains low for at least 3 periods, the capacitor C of the filter 17 is discharged, which causes the opening of the transistor 18 which in turn drives the transistor opening 19 so that the equivalent circuit of the structure is to have the coil in parallel with the voltage drop between the battery 4 and the Zener diode 21. Thus, the relay structure allows rapid demagnetization through the diodes 23 and Zener 21 (slope = (Vbat - Vzenerg) - Note that the demagnetization must be advantageously slow, what is represented in the figure by the arrow A, to maintain a stable current in the coil during the MLI mode but must be fast, which is represented in the figure by the arrow B, when opening the contact to avoid damaging it quickly. The effect of this demagnetization is visible in FIG. 5 on which is represented the current curve passing through the relay coil. The first part shows that during the PWM mode the demagnetization of the coil takes place slowly while after a stop of the function (see Figure 4), the demagnetization becomes fast.

Referring again to FIG. 2, a shunt-type resistor 22 is inserted into the ground-referenced loop to measure the current image. The voltage drop in the resistor must be small enough to limit its impact on the saturation current of the transistor 16 but must nevertheless be sufficiently high to measure a fairly precise voltage level by the analog-digital converter of the microcontroller / control circuit 11 For example, the following criteria for the choice of resistance can be used. First, the value of the resistor will be limited to a voltage drop of the order of volt, typically 1V to 2V maximum for a control voltage of 5V of the transistor 16, while being high enough to be significant (from preferably of the order of 25%) facing the measuring range of the analog-digital converter (typically from 0 to 5V), or advantageously a maximum voltage drop of the order of 1.2V.

Then, a tolerance (initial + temperature drift) of the order of one percent will preferably be selected to limit measurement errors (1% to 2% max). We can still choose a resistor whose power dissipated will be low, preferably well below the Watt. The current flowing through the coil 13 is dependent on the battery level 14 and the value of the resistance of the coil which itself depends on the ambient temperature. The resistance value of the coil can be specifically selected according to the capabilities of the supplier to ensure proper operation of the relay at a minimum voltage level and at maximum temperature. The choice of having a current measurement resistor for each coil of the various relays that can comprise a vehicle, makes it possible to adjust to an optimum current and individually relay relay, and this without considering the battery level or the temperature of the coil. If we consider the same conditions as those taken for the example with a standard structure, we see that the power to be dissipated for a relay whose current through the coil is regulated at -10-

0.e optimal holding value. at 67mA in this example), is significantly lower: Pbob = Ibob2 X Rbob = 0.0672 x 120 = 0.54W; Let in this example a decrease of 1.59W of the power to be dissipated in the coil. Knowing that in most products, several relays coexist, the decrease in power will be all the more important that there will be a large number of relays. In the case of control by switching, the control unit must also dissipate the switching losses considered, these losses being of the order of 10% to 20% maximum of the power supplied. This gives a total power dissipated of the order of 0.59 to 0.65W against 2.13W for a standard structure as shown in Figure 1, an overall saving of the order of 1.38W. FIG. 3 represents a chronogram of activation of a relay in PWM mode. The control signal for pulse width modulated switching control comprises three phases P1 to P3. A first switching phase P1_Com during which the control signal is maintained at a high level for a period of time determined to allow the switching of the relay before the start of the control PWM mode itself. It is indeed necessary to provide sufficient control energy to move the contact mechanically from its open position to its closed position. For this, a continuous command of 100ms can be made to allow switching of the relay before the MLI command. A second maintenance phase P2_MLI during which the control signal is in PWM mode to allow the maintenance of the control even when the battery voltage is low or when starting. In fact, once the mechanical transition is ensured during the first phase, it is no longer necessary to maintain this energy level, hence the operation in PWM control. Finally, the control signal comprises a third release phase P3_Rel during which the signal is at a low level to stop the contact of the switch. The PWM signal frequency should preferably be higher than the audible frequencies (ie 35kHz for domestic animals), and also sufficiently lower than the control stage transition frequency so as to limit switching losses and delay effects. between control and control of the coil (see Figure 6) and to be compatible with the resources of the microcontroller. According to the recommendations of the relay suppliers and the automotive / component constraints, the frequency should advantageously be in a range from 40 kHz to 60 kHz. As indicated above, FIG. 6 represents the evolution of the switching losses with respect to the control signal. The first timing diagram represents an example of the control signal V ~ m of the control transistor 16. The second timing diagram represents the evolution of the current (IT) and of the voltage (VT) at the terminals of this same control transistor and in particular the point of intersection between the two. Finally, the third chronogram represents the losses due to the division in PWM mode. There is a loss of switching during transistor close and open commands and conduction losses during MLI mode. It should be noted for this purpose that the higher the frequency, the greater the loss of switching (invariable) becomes significant face loss in conduction. Indeed, when the frequency increases the time (Ton) during which the transistor is conductive decreases. FIG. 4 schematically represents the servocontrol structure of an electromechanical relay. The control is performed by the microcontroller from the measurement of the voltage across the shunt resistor, which provides an image of the current (Ibob) through the coil. According to the setpoint (Cons_i) desired for a type of relay, the microcontroller adjusts the duty cycle of the PWM signal. For this purpose, the -12-

microcontroller Calculates the necessary duty cycle of the PWM signal to make the measured coil current move towards the setpoint. If the measured current is too low compared to the fixed setpoint, the duty cycle increases and vice versa.

It will be understood that various modifications and / or improvements obvious to those skilled in the art can be made to the various embodiments of the invention described in the present description without departing from the scope of the invention defined by the appended claims. In particular, it is possible to provide a simplified version of the assembly without measuring the current flowing through the coil. This alternative is to use only the information received at the battery for all relays to adjust the duty cycle. Such a version, although economical, is not optimal insofar as it consists in measuring only the battery level through a resistor splitter bridge for adaptation to the voltage range of an analog-to-digital converter. digital, to calculate the duty cycle PWM control signal, cyclic report then common to all relays for example. It will also be noted that the electromechanical relay structure applies more particularly to monostable relays, that is to say of which ~ e3 defl ects switch when the coil is energized and whose return to the ruptured state is done when the coil is no longer excited.

Claims (13)

REVENDICATIONS1. Electromechanical relay designed for the automobile comprising an electromagnet (13) input-controlled by a control circuit (11) and adapted to transmit when energized, a force to a switching circuit (12) for switching output of a power circuit, characterized in that the control circuit comprises means for regulating the current flowing through the electromagnet. 2. Electromechanical relay according to claim 1, characterized in that the regulating means are switching control means made by servocontrolling the average current (Ibob) passing through the electromagnet to a setpoint current by means of a control device. pulse width modulation. 3. electromechanical relay according to claim 2, characterized in that it comprises means for measuring the current (22) passing through the electromagnet (13) and in that the regulating means adjust the duty cycle of the control in modulation of pulse width as a function of the setpoint current and the current measurement. 4. Electromechanical relay according to claim 2 or 3, characterized in that a control signal of the electromagnet comprises a first switching phase (P1_Com), a second holding phase (P2_MLI) during which the modulation control is applied. pulse width and a third release phase (P3_Rel). 5. Electromechanical relay according to claim 4, characterized in that it comprises means for slow demagnetization (20) of the electromagnet during the second holding phase. 6. Electromechanical relay according to claim 5, characterized in that the means of slow demagnetization are constituted by two diodes connected in parallel with the electromagnet during the holding phase. 7. Electromechanical relay according to claim 5 or 6, characterized in that it comprises means for rapid demagnetization (21) of the electromagnet during the third release phase. 8. Electromechanical relay according to claim 7, characterized in that the fast demagnetization means are constituted by a Zener diode paralleling the electromagnet during the release phase. 9. Electromechanical relay according to one of claims 1 to 8, characterized in that the frequency of the control pulse width modulation is selected to be substantially less than the frequency of the transitions of the control circuit. 10. Electromechanical relay according to claim 9, characterized in that the frequency of the pulse width modulation control is selected to be higher than the audible frequencies for the animals. 11. Electromechanical relay according to one of claims 1 to 10, characterized in that the electromechanical relay is a monostable electromechanical relay designed for automotive applications. A motor vehicle motor housing 20 comprising a plurality of electromechanical relays according to any one of the preceding claims. 13. A method of switching an electromechanical relay of a motor vehicle service housing comprising the steps of: - controlling an electromagnet (13) input by a control circuit (11); regulating by slaving the average current (Ibob) passing through the electromagnet to a setpoint current by means of pulse width modulation control; transmitting a force to a switching circuit (12); to output a power circuit,