Safety control devices for electric actuators

Abstract

A pulse width modulated voltage conversion control device for an electric actuator (2) such as a motor comprises at least one power electronic circuit (3) having a first insulated gate field effect transistor (6) electrically connected to an output conductor (7) supplying power to the electric actuator (2) via a first connection device (11a). The first connection device (11a) comprises a first weld and a first device (13) for thermal connection by conduction between the first weld and the body of the first insulated gate field effect transistor (6). The first weld is arranged so that when the body of the first insulated gate field effect transistor (6) exceeds a predetermined temperature threshold, the first weld melts and disconnects the electrical connection between the first insulated gate field effect transistor (6) and the electric actuator (2).

Description

Technical Field

[0001] The invention relates to a control device which allows controlling the speed of movement of an electric actuator, in particular the speed of rotation of a DC motor used to blow air into the exchanger and engine of a motor vehicle in order to cool them. Background Art

[0002] In motor vehicles, the heat exchangers associated with cooling the water used to conduct the heat generated by the internal combustion engine are usually connected to the exchangers used to remove the heat generated by the compression of the gas used for air conditioning by placing them in series in a given cooling air flow. In front of or behind these exchangers, a cooling fan driven in rotation by a DC motor is placed to generate a cooling air flow that must pass through it, thus facilitating the heat exchange. This cooling air flow is then directed to the engine of the vehicle.

[0003] The airflow requirements associated with the pair of "engine cooling exchanger" and "air conditioning exchanger" may range from gentle airflow to maximum airflow:

[0004] - Soft airflow: The vehicle's engine temperature is low, the air conditioning requirement is moderate, and the vehicle is moving, so that its speed already generates airflow.

[0005] - Maximum airflow conditions: The vehicle has come to a stop after a long load ramp, the vehicle's engine has heated up to a higher temperature than normal, and the high outside temperature creates a significant demand on the air conditioning.

[0006] In most cases, this difference in demand can be accounted for by varying the speed of the cooling fan, using a control device that produces a variable voltage at the DC motor's power terminals.

[0007] A first known variable voltage control device uses a series resistor in the power supply circuit of an electric actuator (i.e. a DC motor) which reduces the current and the voltage between the motor terminals for low speed rotation. To rotate the motor at its maximum speed, the resistor is short-circuited. Such a series resistor control device is described, for example, in document FR 2 826 199 A1.

[0008] A second known variable voltage control device uses a pulse width modulation (PWM) voltage conversion electronic device that generates an output voltage that is equal to the input voltage during the conduction step or equal to zero during the non-conduction step, and changes the average value of the output voltage by modifying the ratio of the duration of the conduction step to the non-conduction step. Thus, the rotation speed of the motor can be adjusted more finely and gradually than with the series resistor technique. Such an electronic pulse width modulation control device is described, for example, in document US 6 369533 B1.

[0009] Motor vehicle manufacturers are currently seeking to extend the service life of their vehicles, reduce electrical losses (reducing fuel consumption or extending battery life in electric vehicles), reduce production costs and reduce noise.

[0010] The series resistor technology, which is particularly beneficial from an economic point of view, is not very compatible with extending the life of the vehicle, since, since the series resistor technology is almost entirely based on electromechanical relays, the number of switchings that can occur before failure is limited. Its greatest disadvantage lies in the electrical power losses generated by the series resistor. In particular, the losses can often reach 100% of the power required to drive the fan at the most frequently used operating point.

[0011] PWM voltage conversion technology appears to be a more advantageous solution, although its cost is much higher than the series resistor technology. In this case, in order to perform the conduction step and the non-conduction step, the current supplied to the DC motor is converted by a power electronic circuit including electronic components such as insulated gate field effect transistors (MOSFETs) and power diodes. These electronic components are subjected to non-negligible heating during their operation, and the temperature of their junctions may be as high as about 150°C or 175°C without interrupting their operation. The life of these electronic components is much longer than that of relay-based systems. However, due to the reduction in engine size for ecological reasons, there is currently a trend for the engines of motor vehicles to operate in increasingly hotter atmospheres and increasingly limited spaces (especially in the case of hybrid vehicles). This temperature increase shortens the life of electronic components, especially the life of insulated gate field effect transistors (MOSFETs). In addition, above certain temperatures, electronic components such as insulated gate field effect transistors (MOSFETs) may fail, resulting in the risk of vehicle fire.

[0012] Overvoltages in the vehicle power network can also damage MOSFETs. MOSFETs are also susceptible to damage due to processing errors when incorporating them into circuits. MOSFETs also run the risk of failure due to poor manufacturing.

[0013] Document DE 10 2010 003241 A1 describes a three-phase inverter comprising a power switch for powering a brushless motor of an electromechanical motor vehicle steering device. In order to prevent the power switch from being damaged in the event of an overload or a fault, the document teaches providing at least one safety switch which is connected in series between the power supply and the inverter input and whose disconnection is controlled by a fault or overload detection circuit. The safety switch comprises an elastic conductor, one end of which is fixed by a soldering portion which will melt when a high temperature is generated by a heat source controlled by the fault or overload detection circuit. The accompanying drawings show that the heat source and the soldering portion are arranged at a short distance from each other on respective conductive paths provided on an insulating substrate for a printed circuit. No information is provided about possible specific properties of the insulating substrate of the printed circuit, or about its possible use for conducting heat between the heat source and the soldering portion.

[0014] Document US 2012 / 268854 A1 describes an electronic component provided with an integrated protection device which interrupts the current flowing through the component in the event of overheating of the component. The protection device consists of an electrical conductor of the component, one end of which is attached to a conductive path under elastic load by a soldering portion, which melts and disconnects the circuit in the event of high temperatures due to heat from the component or from the outside. The component and the soldering portion are arranged on corresponding conductive paths provided on an insulating substrate for a printed circuit. No information is provided about possible specific properties of the insulating substrate of the printed circuit, or about its possible use for conducting heat between the component and the soldering portion.

[0015] Document US 2011 / 211284 A1 describes a protection element, which includes a power circuit between two main terminals, the power circuit including a preloaded elastic conductor, which connects two conductive paths connected to the two main terminals to each other through two fusible soldering parts respectively. A resistor powered by an external control circuit allows the fusible soldering part to be heated and melted, thereby disconnecting the power circuit between the two main terminals. An insulating layer (14) is arranged between the resistor and the conductive path. No information is provided about the possible specific properties of the insulating layer, or about its possible use for conducting heat between the resistor and the soldering part. An electrically insulating heat-conducting substrate (11) carries the main terminals and the resistor, but is at a certain distance from the soldering part so that it is not used to conduct heat between the resistor and the soldering part. Summary of the invention

[0016] One problem to be solved by the invention is to limit the risk of damage to electronic components such as insulated gate field effect transistors (MOSFETs) in pulse width modulated voltage conversion electronics for controlling electric actuators, for example by controlling the rotation speed of the motor. An advantageous application is in particular the control of direct current motors for blowing air into the exchanger and engine of a motor vehicle for cooling it.

[0017] At the same time, the present invention aims to effectively limit the risk of fire in such an electronic control device for an electric actuator due to a failure of an electronic component such as an insulated gate field effect transistor (MOSFET).

[0018] To achieve these and other objects, the present invention provides a control device for an electric actuator such as a motor, comprising:

[0019] - a power electronic circuit having a power supply input intended to be connected to a DC power supply, having a power supply output intended to be connected to an electric actuator, comprising a first insulated gate field effect transistor, one side of a source-drain circuit of the first insulated gate field effect transistor being electrically connected to the power supply input, and the other side of the source-drain circuit of the first insulated gate field effect transistor being electrically connected to the power supply output via an output conductor so as to be connected in series with the electric actuator, the power electronic circuit comprising a flyback diode connected to the power supply output in a reverse biased configuration so as to allow a current generated by an inductive element of the electric actuator to flow when the first insulated gate field effect transistor is turned off;

[0020] - a switch controller capable of generating a substantially square wave width modulated control signal on the gate of said first insulated gate field effect transistor,

[0021] The source-drain circuit of the first insulated gate field effect transistor is electrically connected to a heat source via a first connecting device including a first welding portion (soldering portion), and the first connecting device and the heat source are arranged on the same electrically insulating substrate.

[0022] and wherein the first welding portion is arranged so that when the heat emitted by the heat source exceeds a predetermined threshold value, the first welding portion melts and disconnects the electrical connection achieved by the first connecting device;

[0023] According to the present invention:

[0024] - a first connection device capable of disconnecting the electrical connection is arranged between the first insulated gate field effect transistor and the output conductor;

[0025] - the heat source is the first insulated gate field effect transistor itself;

[0026] - the first soldering portion is arranged so that when the temperature of the body of the first insulated gate field effect transistor exceeds a predetermined temperature threshold, the first soldering portion melts and disconnects the electrical connection between the first insulated gate field effect transistor and the electric actuator;

[0027] - the first insulated gate field effect transistor is a SMC (surface mounted component) and is mounted by contact between its body and the substrate;

[0028] - a first soldering portion is arranged in contact with said substrate;

[0029] - The thermal conductivity of the substrate is greater than or equal to 5 W / mK.

[0030] Since the first IGFET is a SMC, its body is in close contact with an electrically insulating substrate made of a material selected for its good thermal conductivity to achieve good heat conduction by conduction, thereby conducting heat generated by the first IGFET to the first soldering portion.

[0031] In fact, the first welding portion contacts the electrical insulation layer of the substrate via a first conductive path of the substrate, and the first conductive path is connected to the source-drain circuit of the first insulated-gate field-effect transistor, while the main body of the first insulated-gate field-effect transistor can be in direct contact with the electrical insulation layer, or in contact with the electrical insulation layer via another conductive path of the substrate.

[0032] In this way, the electrically insulating substrate constitutes a first device for thermally connecting by conduction between the first insulated gate field effect transistor and the first welding portion, thereby enhancing the responsiveness of current interruption when the temperature of the first insulated gate field effect transistor rises, and ensuring that the temperature of the insulated gate field effect transistor that interrupts the current has good accuracy.

[0033] When the temperature of the body of the first insulated gate field effect transistor exceeds a predetermined temperature threshold, the heat conducted by the first thermal coupling device melts the first soldering portion, thereby disconnecting the circuit and interrupting the current flowing through the first insulated gate field effect transistor. The first insulated gate field effect transistor thus stops working before its temperature causes it to fail and / or possibly catch fire. In this way, the first insulated gate field effect transistor is protected and the risk of fire is limited.

[0034] Advantageously, this allows:

[0035] - the first connection means comprises a first terminal lug electrically connected to the source-drain circuit of the first insulated gate field effect transistor through a first soldering portion and electrically connected to the output conductor;

[0036] When the first soldering portion melts, the free end of the first terminal piece moves away from the source-drain circuit of the first insulated gate field effect transistor by elastic recovery or by shape memory.

[0037] The use of a spring-return or shape memory tab can ensure a good degree of separation at the first weld.

[0038] Preferably, when the first terminal tab is connected via the first soldering portion, it may have a non-linear longitudinal profile between the first soldering portion and the output conductor.

[0039] Due to the temperature variations to which the control device is subjected, expansion and contraction effects may occur which cause dimensional changes in the distance between the power electronics circuit and the output conductors. The non-rectilinear longitudinal profile of the lug enables it to deform in the longitudinal direction with low mechanical resistance, allowing these dimensional changes to be absorbed without generating excessive mechanical stresses in the substrate carrying the components of the control device:

[0040] - if the distance between the power electronics circuit and the output conductor is reduced, the lug is further deformed away from the rectilinear longitudinal profile;

[0041] If the distance between the power electronics and the output conductor increases, the lug deforms to more closely approximate a rectilinear longitudinal profile.

[0042] Advantageously, it may be provided that the substrate comprises a ceramic layer.

[0043] The ceramic may be, for example, aluminum oxide (Al2O3) or aluminum nitride (AlN). Since the first insulated gate field effect transistor is an SMC, its body is in close contact with a substrate having a ceramic layer to achieve good heat conduction by conduction in the ceramic layer, the ceramic layer being made of a material selected for its good thermal conductivity, thereby conducting the heat emitted by the first insulated gate field effect transistor to the first welding portion. In practice, the first welding portion is in contact with the ceramic layer via a first conductive path of the substrate, which is connected to a source-drain circuit of the first insulated gate field effect transistor, and the body of the first insulated gate field effect transistor may be in direct contact with the ceramic layer, or in contact with the ceramic layer via another conductive path.

[0044] As an alternative, the substrate may include a metal layer associated with the electrical insulating layer. The material of the metal layer of the substrate is also selected for its good thermal conductivity to conduct the heat emitted by the first insulated gate field effect transistor from the body of the transistor to the first soldering portion. The metal layer may be made of aluminum or an aluminum alloy, or of copper or a copper alloy, for example.

[0045] Advantageously, this allows:

[0046] - In the power electronic circuit, the freewheeling diode is formed by a structured diode of a second insulated gate field effect transistor;

[0047] - the driving means is configured to switch the second insulated gate field effect transistor into a conducting state when the first transistor is in a non-conducting state;

[0048] - a second insulated gate field effect transistor is electrically connected to the output conductor via a second connecting means;

[0049] - the second connection means comprises a second soldering portion and second means for thermal coupling by conduction between the second soldering portion and the body of the second IGFET;

[0050] The second soldering portion is arranged such that when the body of the second insulated gate field effect transistor exceeds a predetermined temperature threshold, the second soldering portion melts and disconnects the electrical connection between the second insulated gate field effect transistor and the electric actuator.

[0051] The second insulated gate field effect transistor exhibits a very low residual resistance in the on-state, which generates much less losses than the junction voltage of a "standard" freewheeling diode in the on-state. In this way, converting the second insulated gate field effect transistor into the on-state allows limiting the losses during the phase in which the freewheeling current flows. However, it must also be noted that the second insulated gate field effect transistor itself does not heat up to a limit that could cause it to fail or even catch fire. Specifically, in the event of a failure of the second insulated gate field effect transistor, the second insulated gate field effect transistor remains in the on-state: when the first insulated gate field effect transistor is converted to the on-state, the DC power supply will be short-circuited. In the case of a motor vehicle, this stops the vehicle battery from working. Therefore, it most advantageously limits the risk of failure of the second insulated gate field effect transistor.

[0052] To this end, when the temperature of the body of the second insulated gate field effect transistor exceeds a predetermined temperature threshold, the heat conducted by the second thermal coupling device melts the second soldering portion, which disconnects the circuit and interrupts the current flowing through the second insulated gate field effect transistor. The second insulated gate field effect transistor thus stops working before its temperature causes it to fail and / or possibly catch fire. In this way, the second insulated gate field effect transistor is protected and the risk of fire is limited.

[0053] For reasons similar to those given above in connection with the first insulated gate field effect transistor, it is also possible that:

[0054] - the connection means comprises a second terminal lug electrically connected to the source-drain circuit of the second insulated gate field effect transistor through a second soldering portion and electrically connected to the output conductor;

[0055] When the second soldering portion melts, the free end of the second terminal piece moves away from the source-drain circuit of the second insulated gate field effect transistor by elastic recovery or by shape memory.

[0056] For reasons similar to those given above in connection with the first insulated gate field effect transistor, it is also possible that the second tab, when connected via the second soldering portion, has a non-linear longitudinal profile between the second soldering portion and the output conductor.

[0057] For reasons similar to those given above in connection with the first insulated gate field effect transistor, it is also possible that:

[0058] - the second insulated gate field effect transistor is a SMC (surface mounted component) and is mounted by contact between its body and a substrate having a thermal conductivity greater than or equal to 5 W / mK;

[0059] - The second soldering portion is arranged in contact with the substrate.

[0060] For reasons similar to those given above in connection with the first insulated gate field effect transistor, it is also possible that:

[0061] - the second insulated gate field effect transistor is an SMC (surface mount component) and is mounted by contact between its body and a substrate including a ceramic layer;

[0062] - The second soldering portion is arranged in contact with the substrate comprising the ceramic layer.

[0063] As an alternative, you can make:

[0064] - the second insulated gate field effect transistor is a SMC (surface mounted component) and is mounted by contact between its body and a substrate comprising a metal layer associated with an electrically insulating layer;

[0065] - A second soldering portion is arranged in contact with a substrate comprising a metal layer associated with an electrically insulating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Other objects, features and advantages of the present invention will become apparent from the following description of specific embodiments with reference to the accompanying drawings, in which:

[0067] Figure 1 is a schematic diagram of a circuit of a first embodiment of a control device for an electric actuator according to the present invention;

[0068] Figure 2 is used to Figure 1 A schematic side view of a specific embodiment of a first arrangement of a control device connected to an output conductor in a closed state;

[0069] Figure 3yes Figure 2 Another schematic side view of the first connecting device in an open state;

[0070] Figure 4 is used to Figure 1 A schematic side view of a specific embodiment of a control device connected to the second device of the output conductor in a closed state;

[0071] Figure 5 yes Figure 4 Another schematic side view of the second connecting device in an open state; and

[0072] Figure 6 is a schematic diagram of a circuit of a second embodiment of a control device for an electric actuator according to the present invention. DETAILED DESCRIPTION

[0073] Figure 1 The circuit diagram of a specific embodiment of the device 1 according to the present invention for controlling an electric actuator 2 is schematically shown. The electric actuator 2 is here an electric motor (also referred to herein as "motor"), but this is by no means a limitation of the present invention.

[0074] The control device 1 comprises a power electronic circuit 3 having a power supply input 4 for connection to a DC power supply and having a power supply output 5 for connection to an electric machine 2. In this case, the DC electric machine 2 is used to blow air into the exchanger and the engine of a motor vehicle in order to cool them. The DC power supply is therefore constituted by the battery of the vehicle.

[0075] The power electronic circuit 3 includes a first insulated gate field effect transistor 6, one side of the source-drain circuit of which is connected to the power input terminal 4, and the other side is connected to the power output terminal 5 through an output conductor 7, so as to be connected in series with the motor 2. The power electronic circuit 3 includes a freewheeling diode 8, which is connected to the power output terminal 5 in a reverse biased configuration. When the first insulated gate field effect transistor 6 is turned off (i.e., in a non-conducting state), the freewheeling diode 8 allows the current generated by the inductive element of the motor 2 to flow.

[0076] The first insulated gate field effect transistor 6 is controlled in this way to allow a pulse width modulated (PWM) voltage conversion, which generates an output voltage between the terminals of the motor 2 that is either equal to the input voltage during the steps in which the first insulated gate field effect transistor 6 is turned on, or equal to zero during the steps in which the first insulated gate field effect transistor 6 is turned off, and the average value of this output voltage is varied by modifying the ratio of the duration of the steps in which the first insulated gate field effect transistor 6 is turned on and off. Thus, the speed of the motor 2 is controlled so as to gradually adapt it to the vehicle's needs regarding cooling.

[0077] exist Figure 1In the embodiment shown, the freewheeling diode 8 is actually formed by the structure diode of the second insulated gate field effect transistor 16 .

[0078] The control device 1 comprises a microcontroller 10 or a switch controller 9 which is capable of generating a substantially square-wave pulse width modulated control signal at the gate of the first insulated gate field effect transistor 6 .

[0079] The microcontroller 10 also constitutes a driving means configured to switch the second insulated gate field effect transistor 16 into a conducting state during certain steps in which the first transistor 6 is in a non-conducting state.

[0080] The first insulated gate field effect transistor 6 is electrically connected to the output conductor 7 via a first connecting means 11 a .

[0081] The second insulated gate field effect transistor 16 is electrically connected to the output conductor 7 via a second connecting means 11 b.

[0082] exist Figure 2 , the first connection means 11a is shown in more detail with respect to the first insulated gate field effect transistor 6, which in this case comprises a first soldering portion 12 and a first device 13 for thermal connection by conduction between the first soldering portion 12 and the body 6a of the first insulated gate field effect transistor 6. In practice, the first device 13 for thermal connection by conduction is constituted by an electrically insulating substrate 15 and exhibits good thermal conductivity. The first soldering portion 12 is in contact with the electrically insulating layer of the substrate 15 via a first conductive path (not shown in the figure) of the substrate 15, which is connected to the source-drain circuit of the first insulated gate field effect transistor 6. The body 6a of the first insulated gate field effect transistor 6 is an SMC, which can be in direct contact with the electrically insulating layer or in contact with the electrically insulating layer via another conductive path of the substrate 15. The first soldering portion 12 is arranged and configured so that: when the temperature of the body 6a of the first insulated gate field effect transistor 6 exceeds a predetermined temperature threshold, the first soldering portion 12 melts and disconnects the electrical connection between the first insulated gate field effect transistor 6 and the output conductor 7 (thereby interrupting the electrical connection between the first insulated gate field effect transistor 6 and the motor 2). For example, the first soldering portion 12 may be a soldering portion made of a lead-free tin alloy, the melting point of which is approximately 210°C.

[0083] Advantageously, the first connection means 11a may comprise a first terminal tab 14, which is electrically connected to the source-drain circuit of the first insulated gate field effect transistor 6 and to the output conductor 7 via the first soldering portion 12. More specifically, the first terminal tab 14 extends between a first end 14a held in the first soldering portion 12 and a second end 14b electrically connected to the output conductor 7. In practice, the electrical connection between the second end 14b and the output conductor 7 may be formed, for example, by a connection that is not easily broken under the breaking conditions of the first soldering portion 12. For example, a soldering portion made of a metal having a higher melting point than the metal used in the first soldering portion 12 may be used. Electric welding or laser welding may also be used.

[0084] exist Figure 4 1 shows the second connection means 11b in more detail with respect to the second insulated gate field effect transistor 16, which in this case comprises a second soldering portion 17 and a second device 18 for thermal coupling by conduction between the second soldering portion 17 and the body 16a of the second insulated gate field effect transistor 16. The second soldering portion 17 is arranged and constructed so that: when the temperature of the body 16a of the second insulated gate field effect transistor 16 exceeds a predetermined temperature threshold, the second soldering portion 17 melts and disconnects the electrical connection between the second insulated gate field effect transistor 16 and the output conductor 7 (thereby interrupting the electrical connection between the second insulated gate field effect transistor 16 and the motor 2). For example, the second soldering portion 17 can be a soldering portion made of a lead-free tin alloy, whose melting point is about 210°C.

[0085] Advantageously, the second connection means 11b may include a second shape memory tab 19, which is electrically connected to the source-drain circuit of the second insulated gate field effect transistor 16 through the second welding portion 17 and is electrically connected to the output conductor 7. More specifically, the second shape memory tab 19 extends between a first end 19a held in the second welding portion 17 and a second end 19b electrically connected to the output conductor 7. In practice, the electrical connection between the second end 19b and the output conductor 7 may be formed, for example, by a connection that is not easily broken under the breaking conditions of the second welding portion 17. For example, a welding portion made of a metal having a higher melting point than the melting point of the metal used in the first welding portion 12 may be used. Electric welding or laser welding may also be used.

[0086] If the temperature of the body 6a of the first IGFET 6 rises above a predetermined threshold, the first soldering portion 12 melts, and the first free end 14a of the first terminal 14 moves away from the first soldering portion 12 (and thus away from the source-drain circuit of the first IGFET 6) by elastic recovery or by the shape memory of the first terminal 14, as shown in FIG. Figure 3Accordingly, if the temperature of the body 16a of the second IGFET 16 rises above a predetermined threshold, the second soldering portion 17 melts, and the first free end 19a of the second terminal tab 19 moves away from the second soldering portion 17 (and thereby away from the source-drain circuit of the second IGFET 16) by elastic recovery or by shape memory of the second terminal tab 19, as shown in FIG. Figure 5 shown.

[0087] It should be noted that when the first terminal piece 14 and the second terminal piece 19 are connected to the first welding portion 12 and the second welding portion 17, respectively ( Figure 2 and Figure 4 ), they have a non-linear longitudinal profile (along the length direction II) between the first welding portion 12 or the second welding portion 17 and the output conductor 7. In this case, the first terminal piece 14 and the second terminal piece 19 are bent.

[0088] The shapes of the first terminal lug 14 and the second terminal lug 19 are as follows:

[0089] If the distance between the power electronic circuit 3 and the output conductor 7 is reduced, the first lug 14 and the second lug 19 are allowed to exhibit even greater deformations, which thus tend to increase the non-rectilinear nature of the longitudinal profiles of the lugs 14 and 19;

[0090] If the distance between the power electronic circuit 3 and the output conductor 7 increases, the non-rectilinear nature of the longitudinal profile of the lugs 14 and 19 is allowed to decrease, the lugs 14 and 19 thus deforming towards a more rectilinear longitudinal profile.

[0091] exist Figure 2 and 3 As can be seen in the figure, in order to provide an effective thermal connection between the first soldering portion 12 and the first insulated gate field effect transistor 6, the first means 13 for thermal connection by conduction comprises a substrate 15 comprising a layer made of ceramic having high thermal conductivity, to which the body 6a of the first insulated gate field effect transistor 6 is fixed (the first insulated gate field effect transistor 6 is an SMC-surface mount component), and the first soldering portion 12 is in contact with the conductive path of the substrate 15 comprising the ceramic layer. The good inherent thermal conductivity of the ceramic thus selected provides a good degree of thermal connection between the body 6a of the first insulated gate field effect transistor 6 and the first soldering portion 12.

[0092] Similarly, in Figure 4 and 5It can be seen that in order to provide effective thermal connection between the second welding portion 17 and the second insulated gate field effect transistor 16, the second device 18 for thermal connection by conduction includes a substrate 15, which includes a layer made of ceramic with high thermal conductivity, the body 16a of the second insulated gate field effect transistor 16 is fixed to the layer (the second insulated gate field effect transistor 16 is an SMC-surface mount component), and the second welding portion 17 is in contact with the conductive path of the substrate 15 including the ceramic layer.

[0093] Among ceramics exhibiting good thermal conductivity, the following ceramics can be selected, for example, to produce the ceramic layer of the substrate 15 carrying the insulated gate field effect transistors 6 and 16: aluminum oxide (AL2O3) allowing a substrate 15 with a thermal conductivity of approximately 30 W / mK to be obtained, or aluminum nitride (AlN) allowing a substrate 15 with a thermal conductivity of approximately 200 W / mK to be obtained.

[0094] As an alternative to a substrate 15 comprising a ceramic layer, a substrate 15 comprising a metal layer associated with an electrically insulating layer may be used. The electrically insulating layer may consist of a thermally conductive dielectric.

[0095] The metal layer is made of a metal or metal alloy with high thermal conductivity. For example, the following materials can be selected to produce the metal layer of the substrate 15 carrying the insulated gate field effect transistors 6 and 16: aluminum with a thermal conductivity of about 30W / mK, or copper with a thermal conductivity of about 200W / mK. The metal layer is covered with a thermally conductive dielectric layer, whose thermal conductivity is about 8W / mK. In comparison, a substrate made of glass fiber reinforced epoxy resin generally has a thermal conductivity of about 0.8W / mK.

[0096] In any case, in order to ensure effective thermal coupling between the first soldering portion 12 (or the second soldering portion 17) and the first SMC insulated gate field effect transistor 6 (or the second transistor 16), the first means 13 for thermal coupling by conduction (or the second means 18 for thermal coupling by conduction) comprises a substrate 15 having a thermal conductivity greater than or equal to 5 W / mK. The first soldering head 12 (or the second soldering head 17) is arranged in contact with the substrate 15.

[0097] exist Figure 1 In the first embodiment shown, the first insulated gate field effect transistor 6 is subjected to the greatest stress during operation due to the full load current flowing through it. This first embodiment allows the use of an N-type MOSFET as the first transistor 6. This is particularly advantageous in terms of cost: for an equivalent internal resistance, an N-type MOSFET is significantly cheaper than a P-type MOSFET.

[0098] Figure 6A second embodiment is shown which is very similar to the first embodiment: those elements denoted by the same reference numerals as used in the context of the first embodiment are the same elements as those described in the context of the first embodiment.

[0099] This second embodiment differs from the first embodiment in that the electric actuator (motor) 2 is connected between the output conductor 7 and ground potential.

[0100] This second embodiment is less advantageous in terms of cost: one side of the source-drain circuit of the first insulated gate field effect transistor 6 is connected to the power input terminal 4, and the other side is connected to the power output terminal 5 through the output conductor 7 to be connected in series with the electric actuator 2. The first insulated gate field effect transistor 6 is a P-type MOSFET in this case, so it is more expensive for equivalent internal resistance. However, since the electric actuator (motor) 2 is arranged between the output conductor 7 and the ground potential, and since the housing of most motors (electric actuators) is electrically connected to the ground potential, this second embodiment is more advantageous than the first embodiment in terms of electromagnetic compatibility.

[0101] In the two embodiments that have been explicitly described, the freewheeling diode 8 is constituted by the structural diode of the second insulated gate field effect transistor 16. These two embodiments allow the energy losses generated during the freewheeling operation to be reduced by the low internal resistance of the second insulated gate field effect transistor in its on state. However, in certain applications, in particular if the conditions of use (ambient temperature, current magnitude in the electric actuator) permit, it may be advantageous to use a simple power diode as the freewheeling diode 8, which is cheaper than an insulated gate field effect transistor, without departing from the context of the present invention.

[0102] The invention is not limited to the embodiment that has been explicitly described, but encompasses modifications and extensions of this embodiment that are covered by the scope of the appended claims.

Claims

1. A control device (1) for an electric actuator (2), comprising: - a power electronic circuit (3) having a power supply input (4) intended to be connected to a DC power supply, having a power supply output (5) intended to be connected to the electric actuator (2), and comprising a first insulated gate field effect transistor (6), one side of the source-drain circuit of the first insulated gate field effect transistor being electrically connected to the power supply input (4) and the other side being electrically connected to the power supply output (5) via an output conductor (7) so as to be connected in series with the electric actuator (2), the power electronic circuit (3) comprising a freewheeling diode (8) connected to the power supply output (5) in a reverse biased configuration so as to allow the current generated by the inductive element of the electric actuator (2) to flow when the first insulated gate field effect transistor (6) is turned off; - a switch controller (9) capable of generating a substantially square-wave width modulated control signal at the gate of the first insulated gate field effect transistor (6), The source-drain circuit of the first insulated gate field effect transistor (6) is electrically connected to a heat source (6) via a first connecting device (11a), the first connecting device comprising a first welding portion (12), the first connecting device and the heat source being arranged on the same electrically insulating substrate (15), and wherein the first welding portion (12) is arranged such that: when the heat emitted by the heat source (6) exceeds a predetermined threshold, the first welding portion (12) melts and disconnects the electrical connection achieved by the first connecting device, in: The first connection device (11a) capable of disconnecting the electrical connection is arranged between the first insulated gate field effect transistor (6) and the output conductor (7); - the heat source is the first insulated gate field effect transistor (6) itself; - the first soldering portion (12) is arranged so that: when the temperature of the body (6a) of the first insulated gate field effect transistor (6) exceeds a predetermined temperature threshold, the first soldering portion (12) melts and disconnects the electrical connection between the first insulated gate field effect transistor (6) and the electric actuator (2); - the first insulated gate field effect transistor (6) is a surface mounted component and is mounted by contact between its body (6a) and the substrate (15); - the first welding portion (12) is arranged to be in contact with the substrate (15); - The thermal conductivity of the substrate is greater than or equal to 5 W / mK.

2. The control device (1) according to claim 1, wherein: - the first connection device (11a) comprises a first terminal lug (14), the first terminal lug being electrically connected to the source-drain circuit of the first insulated gate field effect transistor (6) through the first soldering portion (12) and electrically connected to the output conductor (7); - When the first soldering portion (12) melts, the free end (14a) of the first terminal piece (14) moves away from the source-drain circuit of the first insulated gate field effect transistor (6) by elastic recovery or shape memory.

3. The control device (1) according to claim 2, wherein: When the first terminal lug (14) is connected via the first welding portion (12), the first terminal lug has a non-linear longitudinal profile between the first welding portion (12) and the output conductor (7).

4. The control device (1) according to claim 1 or 2, wherein: The substrate (15) comprises a ceramic layer.

5. The control device (1) according to claim 1 or 2, wherein: The substrate (15) comprises a metal layer associated with an electrically insulating layer.

6. The control device (1) according to claim 1 or 2, wherein: - In the power electronic circuit (3), the freewheeling diode (8) is formed by a structured diode of a second insulated gate field effect transistor (16); - a driving device configured to switch the second insulated gate field effect transistor (16) into a conducting state when the first insulated gate field effect transistor (6) is in a non-conducting state; - the source-drain circuit of the second insulated gate field effect transistor (16) is electrically connected to the output conductor (7) via a second connecting means (11b); - the second connection means (11b) comprises a second soldering portion (17) and second means (18) for thermal coupling by conduction between the second soldering portion (17) and the body (16a) of the second insulated gate field effect transistor (16); - the second soldering portion (17) is arranged so that: when the temperature of the body (16a) of the second insulated gate field effect transistor (16) exceeds a predetermined temperature threshold, the second soldering portion (17) melts and disconnects the electrical connection between the second insulated gate field effect transistor (16) and the electric actuator (2).

7. The control device (1) according to claim 6, wherein: - the second connection device (11b) comprises a second terminal lug (19), the second terminal lug being electrically connected to the source-drain circuit of the second insulated gate field effect transistor (16) through the second soldering portion (17) and electrically connected to the output conductor (7); - When the second soldering portion (17) melts, the free end (19a) of the second terminal piece (19) moves away from the source-drain circuit of the second insulated gate field effect transistor (16) by elastic recovery or shape memory.

8. The control device (1) according to claim 7, wherein: When the second terminal lug (19) is connected via the second soldering portion (17), the second terminal lug has a non-linear longitudinal profile between the second soldering portion (17) and the output conductor (7).

9. The control device (1) according to claim 6, wherein: - the second insulated gate field effect transistor (16) is a surface mounted component and is mounted by contacting its body (16a) with a substrate (15) having a thermal conductivity greater than or equal to 5 W / mK; - The second soldering portion (17) is arranged in contact with the substrate (15).

10. The control device (1) according to claim 6, wherein: - the second insulated gate field effect transistor (16) is a surface mounted component and is mounted by contact between its body (16a) and a substrate (15) comprising a ceramic layer; - The second soldering portion (17) is arranged in contact with the substrate (15) comprising a ceramic layer.

11. The control device (1) according to claim 6, wherein: - the second insulated gate field effect transistor (16) is a surface mounted component and is mounted by contact between its body (16a) and a substrate (15) comprising a metal layer associated with an electrically insulating layer; - said second soldering portion (17) is arranged in contact with said substrate (15) comprising a metal layer associated with an electrically insulating layer.

12. The control device (1) according to any one of claims 1 to 3, wherein: The electric actuator (2) is an electric motor.

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