FR2802361A1 - Increasing vehicle alternator starting power by feeding rotor winding at high initial voltage which reduces to normal voltage then reverses polarity to give rapid demagnetization and avoid stalling - Google Patents

Abstract

The starting power of a vehicle alternator is increased by applying an increased initial voltage for example 20 V instead of 12 V to the rotor winding. A high starting torque is obtained and to avoid overheating the voltage is reduced to normal during the latter part of the starting phase. On moving to use as an alternator the polarity of the rotor winding voltage is reversed to give rapid demagnetization and avoid engine stalling.

Description

Improvement in devices and methods for controlling the supply of a rotor winding of an electric machine such as a vehicle alternator-starter, in particular automobile. The present invention relates to controlling the power supply to the rotor winding of a rotary electric machine such as an alternator-starter of a vehicle, in particular a motor vehicle.

Such a machine is described for example in documents FR-A-2 745 444 and FR-A-2 745 445 to which we can refer for more details.

This machine operates, on the one hand, as an electric current generator and, on the other hand, as an electric motor. This machine of the polyphase and reversible type therefore operates as an alternator in particular for charging the vehicle battery and as a starter for driving the internal combustion engine, also called heat engine, of the motor vehicle for starting it.

For this purpose the rectifier bridge at the output of the armature the alternator also serves as a bridge for controlling the phases of the alternator.

In known manner, this rotating machine forming an alternator comprises a wound rotor constituting the inductor conventionally associated with two slip rings and two brushes by which the excitation current is brought; - polyphase stator carrying several coils or windings, constituting the armature, which are connected in star or in triangle in the most frequent case of a three-phase structure which deliver towards the rectifier bridge, in alternator operation, the converted electrical power.

The bridge is connected to the different phases of the armature and is mounted between earth and a battery supply terminal. bridge has for example diodes associated with MOSFET type transistors. The operation in engine mode of such an alternator is effected by imposing for example a direct current in the inductor and by delivering synchronously on the stator phases signals phase shifted by 120, ideally sinusoidal but possibly trapezoidal or square.

This rectifier and control bridge is controlled by an electronic control module. The bridge and the control module belong to a unit, known as the control unit, most often located outside the machine.

I1 is further provided means for monitoring the angular position of the rotor to, in electric motor mode, .ect at the right time electric current in the relevant winding of the stator.

These means, advantageously of the magnetic type, send information to the electronic control module and are described for example in documents FR-00 14927 filed on November 20, 2000 and FR-00 03131 filed on March 10, 2000.

These means therefore comprise a target locked in rotation on the rotor or the pulley of the machine and at least one sensor of the Hall effect or magneto-resistive type detecting the passage of the target advantageously of the magnetic type.

Preferably at least three sensors are provided, these being carried by the front or rear bearing that comprises the rotary electrical machine for fixedly supporting the stator and rotating the rotor.

In some cases, it is desired to improve the starting performance of an alternator-starter.

An object of the invention is to respond to this wish.

More particularly, the invention provides a device for supplying the winding of a rotor of an alternator-starter of a vehicle, especially an automobile, suitable for operating as an electric generator in an alternator mode and for operating the engine in a starter mode, characterized in that it comprises means for overexciting the rotor winding to maximize the starting torque of the alternator-starter. Thanks to the invention, it is possible to maximize the starting torque of the alternator-starter when it is operating in starter mode, that is to say in electric motor, which makes it possible to increase the power.

alternator-starter can therefore start an internal combustion engine of a more powerful motor vehicle and / or start said engine under low temperatures.

This overexcitation can be achieved by an overvoltage at the terminals of the excitation winding and / or an overcurrent in the excitation winding with respect to a conventional alternator.

This can be achieved by using an electronic booster or by acting on the number of turns of the excitation winding and on its resistance in order to obtain a higher number of amperes under the same supply voltage.

In one embodiment, the cross section of the conducting wire of the excitation coil is increased. You can play on the number of turns of the excitation coil.

In one embodiment, the rotor winding is overexcited only in start-up mode.

In another embodiment, the rotor winding is also excited in alternator mode.

Such a device is advantageously supplemented by the following different characteristics taken alone or in all their possible combinations - comprises a means for supplying the rotor consisting of a voltage booster circuit.

- Has a means for supplying the rotor consisting of a rotor winding having a low resistance to obtain, under the same supply voltage, a higher number of ampere-turns.

- includes a fast demagnetization circuit, to avoid stalling of the heat engine during the transition from the start function to the alternator function, and to protect, in alternator mode, the clipping diodes against high energy overvoltages produced during load-dump.

- It comprises an inductor mounted between a point for supplying voltage to said device and a switch which is also connected to ground, a branch mounted in parallel to said switch and which comprises in series a capacitor (CB) and a diode ( DB), the anode of this diode (DB) being connected to the inductance (LB), its cathode being connected to the capacitor (CB), the capacitor (CB) being mounted between this diode (DB) and the ground, a point between the cathode of the diode (DB) and the capacitor (CB) being connected to said winding (LEXC) via a switch (T2), a switch (T1) being mounted with a diode (D1) between the positive supply line of the network and the ground, the diode (D1) passing from ground to the switch (T1), its anode being connected to ground, a point between the switch (T1) and the diode ( D1) being connected to a point between the rotor winding LEXC and the switch (T2) by a diode (D2) q ui is passing from the switch (T1) to the rotor winding (LEXC), the rotor winding (LEXC) being connected by a diode (D3) to the power supply of the on-board network, this diode (D3) being conducting from the rotor winding to said mains voltage line, the point common to the rotor winding and the diode. (D3) being connected to ground by a switch (TDMG) which controls rapid demagnetization.

- It includes an inductor mounted between switch (T2) connected to a point for supplying voltage to said device and a switch (TB) which is also connected to 1a branch branch mounted in parallel to said switch and which includes in series a capacitor (CB) and diode (DB), the anode this diode (DB) being connected to the inductor (LB), its cathode being connected to the capacitor (CB), the capacitor (CB) being mounted between this diode (DB ) and ground, point common to said diode (DB) and to the capacitor (CB) being connected to said winding LEXC), a switch (T1) being mounted with a diode (D1) between the positive supply line of the network and the ground, the diode (Dl) passing from ground to the switch (Tl), its anode being connected to ground, a point between the switch (T1) and the diode (D1) being connected to the end of the rotor winding (LEXC) opposite the inductance (LB).

- It includes an inductor (LB) mounted between the positive supply line and ground, a diode (DB) mounted between the end of said inductor (LB) which is opposite to ground and a capacitor (CB) which is connected to ground at its opposite end to said diode (DB), the point common to the diode (DB) and to the capacitor (CB) being connected to the negative potential of the rotor winding (LEXC), the opposite end of said winding being as for it connected by a switch (TDMG) to the earth of the on-board network, a switch (T1) being mounted between the point common to the inductance (LB) and the diode (DB) and a power supply terminal to the battery voltage, the switch (TDMG) connected to the rotor winding being a MOSFET transistor, a Zener diode (DZ) being mounted between the gate of said transistor and its drain connected to the earth of the on-board network), being bandwidth in Zener mode from ground to grid.

- it includes inductor (LB) mounted between the positive supply line and ground, a diode (DB) mounted between the end of said inductor (LB) which is opposite to ground and a capacitor (CB) is connected to the mass at its end opposite to said diode (DB), the point common to the diode (DB) and to the capacitor (CB) being connected to the negative potential of the rotor winding (LEXC), the opposite end of said winding being it connected to the earth of the on-board network, a switch (T1) being mounted between the point common to the inductance (LB) and to the diode (DB) and a supply terminal at the battery voltage.

- it includes a switch (T1) mounted between the input of the excitation winding (LEXC) and the supply line (B +) of the battery, a switch (T2) mounted between earth and the output of the winding (LEXC ), a demagnetization diode (DDMG), mounted between the input of the excitation coil (LEXC) and ground, the anode of the diode (DDMG) being connected to ground, and a diode (DRL) mounted between the terminal (B +) and the output of the excitation coil (LEXC), the cathode of the diode (DRL) being connected to the supply line (B +).

it includes an excitation winding (LEXC) having its output connected to ground, and its input connected to the power supply terminal (B +) via a transistor (T1) mounted in parallel with the diode (Dl) whose cathode is connected to the power supply terminal (B +), the input of the excitation winding (LEXC) is connected to ground via a diode (D3) connected in series with a switch (T2) on the side of its anode, said transistor (T2) being mounted in parallel with a diode (D2) whose cathode is connected to ground.

The invention also relates to a method for controlling the supply of a rotor winding of an alternator-starter of a vehicle, especially automobile, characterized in that said winding is overexcited for a first period after closure of the vehicle's contact switch and in that the voltage level is reduced after a given period before the vehicle's engine starts.

Advantageously - for controlling the supply of a rotor winding of a generator-starter, the excitation voltage is reversed for a given period when the start of the vehicle's heat engine is detected.

- a parameter is controlled which is a function of the voltage at the terminals of the excitation winding and / or of the current in this excitation winding to maintain this parameter permanently on the same side with a threshold value which corresponds to a maximum temperature admissible for the electric machine and its components.

- the temperature of a characteristic component is determined and the control parameter is controlled so that this temperature is permanently equal to or lower than a maximum admissible temperature for the electric machine and its components. - The angular speed of the rotating part of the machine is measured and in that the control parameter is compared with a threshold value which is a function of the angular speed of the rotor.

- the control parameter is a function of voltage or current at the output of a circuit generating overexcitation voltage and this circuit is controlled to maintain the control parameter with respect to the threshold value.

- Checking the duty cycle of a pulse width modulation signal which controls a switch itself controls the supply of the excitation winding, to maintain this duty cycle less than or equal to a threshold duty cycle.

- the temperature control is activated by measuring the temperature of the hottest component and comparing it to a reference voltage.

- The control is implemented by estimating the temperature of the hottest component from a temperature easy to measure.

Thanks to these characteristics, a device is provided for controlling the supply of the excitation winding (that is to say the rotor winding) in starter mode, making it possible to quickly install the starting torque, to increase it and to minimize heat dissipation and maximize starting power.

It is easier to stop the internal combustion engine of the motor vehicle at a red light and then restart. During this stop at red light, the machine, in one embodiment, operates as an electric motor and can lead, thanks to the overexcitation, to a greater number of consumers, such as the air conditioning compressor, the power steering, etc.

This machine then operates as an auxiliary motor as described for example in document EP-0 715 979. Advantageously, rapid demagnetization, that is to say rapid deactivation of the excitation winding by stopping the excitation current, is carried out at the end of starter mode so that the engine of the vehicle which has just started - idle speed - does not stall when switching to alternator mode.

Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and not limiting and should be read with reference to the appended drawings in which - Figure 1 is a schematic representation illustrating a supply circuit conforms to a possible implementation mode for the invention; - Figure 2 is a graph on which a curve has been plotted illustrating the pace in alternator mode, as a function of angular speed of the rotor of the starter alternator, of the temperature of the hottest component of the machine on the one hand in the case of an air-cooled alternator-starter and on the other hand in the case of an alternator cooled by a water circuit; it can be seen that in certain speed zones, the maximum admissible temperature is not reached, hence one of the objects of the invention, namely to control the temperature of a representative component at the maximum admissible temperature.

- Figure 3 is a graph on which a curve has been plotted illustrating the shape, as a function of the angular speed of the rotor of the alternator-starter, of the voltage or of the maximum admissible current at the terminals of the excitation winding alternator-starter, in the case of a command according to possible implementation mode of the invention; - Figure 4 is a graph on which a curve has been plotted illustrating the shape, as a function of the rotor angular speed of the alternator-starter, of the maximum admissible duty cycle at the terminals of the excitation winding of the alternator-starter in the case of an order conforming to a possible embodiment of the invention; - Figure 5 is a schematic representation illustrating a possible embodiment for a circuit for controlling the supply of a rotor winding, comprising a voltage rise or electronic boost assembly; - Figure 6 illustrates the shape of the voltage across the excitation winding in motor vehicle starter mode in accordance with a preferred start command sequence; - Figures 7 to 9 are schematic representations similar to that of Figure 5 illustrating other possible embodiments; - Figures 10 and 11 are schematic representations similar to those of Figure 5 for still other embodiments; - Figure 12 is a graph showing a flow curve (intensity of the current delivered) in alternator mode depending on the number (nb) of revolutions per minute of the rotor for yet another embodiment.

In the figures the rotary electric machine of the polyphase type is an alternator-starter of the above-mentioned type is described for example in the documents FR-00 14927 FR-00 03131 mentioned above.

This machine has here the structure of a conventional alternator, example of the type described in document EP-A-0 515 to which reference will be made for more details.

This machine is therefore internally ventilated (air cooled), its rotor carrying at least one of its axial ends a fan. As a variant, the machine is cooled by water.

More precisely, the rotor is a claw rotor with polar wheels carrying on their outer periphery teeth of axial orientation and trapezoidal shape. The teeth of one pole wheel are directed towards the teeth of the other pole wheel, said teeth of generally trapezoidal shape being distributed in a nested fashion from one pole wheel to another.

Of course, as described for example in document FR-A-2 085, permanent magnets can be inserted between the teeth of the pole wheels to increase the magnetic field.

The rotor carries an excitation winding between the flanges of its pole wheels. This winding comprises an electrically conductive element which is wound with the formation of turns. This winding is an excitation winding which, when activated, magnetizes the rotor to create, using the teeth, magnetic poles. The ends of the rotor winding are each connected to a slip ring on each of which rubs a brush. The brushes are carried by a brush holder secured to the rear bearing of the machine centrally carrying a ball bearing rotatably supporting the rear end of the shaft carrying the rotor to join.

The front end of the shaft is rotatably supported by a ball bearing carried by the front bearing of the machine. The front end of the shaft carries outside the machine a pulley belonging to a movement transmission device comprising at least one belt engaged with the pulley. The motion transmission device establishes a connection between the pulley and a member, such as another pulley, driven in rotation by the internal combustion engine of the vehicle.

When the machine - here an alternator-starter operates in alternator mode, that is to say as an electric generator, the pulley is rotated by the internal combustion engine of the vehicle via at least the aforementioned belt. When the machine operates in starter mode, that is to say in electric motor, the pulley rotates the vehicle engine via the belt.

The front and rear bearings are perforated for internal ventilation of the machine, are connected between, for example using tie rods, and belong to the support of the machine intended to be fixed on a fixed part of the vehicle. This support carries in a fixed manner at its external periphery stator usually constituted by a pack of sheets provided with notches for mounting the coils or more generally the stator windings whose outputs are connected to the aforementioned control rectifier bridge.

The stator coils or windings are formed by wires or bar windings as described for example in document WO92 / 06527; the bars can be of rectangular section ...

The stator surrounds the rotor, the brushes of which are connected to an alternator regulator to maintain the alternator voltage at a desired voltage here of the order of 14V, for a 12V battery.

The rectifier bridge, the electronic rectifier bridge control unit and the regulator are here mounted in an electronic box located outside the machine. This housing carries (FIG. 1) switching means 2, here comprising power switches, a control unit 3 and overexcitation circuit 1.

The assembly which is represented in FIG. 1 comprises a starter alternator whose stator windings and the rectifier bridge, referenced by ALT, are mounted in parallel with a battery B of a vehicle and whose excitation winding EXC brought to be secured by the rotor is supplied via an overexcitation circuit 1.

This overexcitation circuit is active in start-up mode (alternator-starter operating with an electric motor) in order, according to the invention, to maximize the start-up torque of the alternator-starter and to more easily start the internal combustion engine, also called thermal engine, of the motor vehicle, either during a cold start, or during a restart after, for example, a stop at a red light: the engine having been switched off to reduce fuel consumption and thus perform a so-called Stop and GO.

This overexcitation circuit 1 receives as input the on-board network voltage delivered by the battery and / or the alternator and delivers at the terminals of the excitation winding EXC a voltage greater than this on-board network voltage. The assembly shown in FIG. 1 furthermore includes switching means 2 (power switch for example) controlled by a control unit 3.

This control unit 3 is for example constituted by the regulator of the alternator and controls the switch 2 by signal with pulse width modulation.

 Also, the control unit 3 may include means which make it possible, in the case where the alternator-starter is discharged on the on-board network while being disconnected relative to the battery (case of load dump according to English terminology generally used by those skilled in the art), to immediately control the opening of the power switch 2, in order to achieve rapid demagnetization of the alternator, in particular of its rotor.

The overexcitation circuit 1 also acts when the machine is operating in alternator mode.

The overexcitation circuit 1 is controlled so that the overexcitation voltage or current which it delivers is always less than a voltage or a current corresponds to the maximum admissible temperature for the alternator-starter and the components which are associated with it. ci, especially when the machine works in alternator mode.

In a first mode of implementation, there is provided on the machine at least one thermal sensor which allows to know with precision the temperature of the hottest element.

A control loop makes it possible to maintain the voltage and / or the overexcitation current delivered by the excitation circuit 1 at values which permanently require the machine, in particular in alternator mode, to be at a temperature below the maximum admissible temperature for this one and components.

According to a characteristic of this embodiment, when the machine operates in starter mode, in particular to start the motor vehicle, the overexcitation (voltage and / or current delivered by the overexcitation circuit) is greater than the overexcitation in alternator mode in order to maximize the starting torque (and therefore the power) of the alternator-starter.

According to the invention, the rotor current is magnetized, that is to say the current of the excitation winding, with a current greater than that required in alternator mode.

As a variant, it is possible to act on the excitation voltage and increase it relative to the alternator mode.

In another mode of implementation, which is a preferred mode of implementation, the overexcitation circuit 1 is controlled so that the voltage or the current which it delivers is always less than a voltage or a current which , for a given angular speed for the rotor, in particular in alternator mode, would correspond to a maximum temperature predetermined by tests or another means.

In particular, it is known that the temperature of an alternator and of components - that is to say of the parts which constitute it varies, as a function of the angular speed of the rotor, according to curves of the type of those represented in the figure in the case an air cooled machine (solid line curve) or a water cooled machine (dashed line curve). In addition, the maximum permissible temperature (shown in 2-point dashed line) is a horizontal straight line cutting the temperature curves of the machine or its components to their maximum (speed of approximately 3000 rpm).

It is of course possible to reverse these curves for. deduce therefrom a maximum overexcitation voltage Vs as a function of the angular speed of the rotor.

Curves in this direction are illustrated in Figure 3.

The overexcitation circuit 1 is controlled, as a function of the angular speed of the rotor, so that the voltage Vs or the overexcitation current that the circuit 1 delivers is always less than the voltage or the maximum current which corresponds to this angular speed.

The machine is thus used in alternator mode to the maximum of its possibilities. In another variant, as illustrated in the figure, it can be foreseen that it is the duty cycle of the pulse width modulation signal which controls the switch 2 which is controlled, either as a function of the temperature or as a function of the angular speed of the rotor, so that the temperature of the hottest component of the machine is always lower than the maximum admissible temperature.

starter mode, a higher duty cycle is used here than in alternator mode. For example, the duty cycle is 100s in starter mode and 75% in alternator mode.

implementation of this temperature control can be achieved by measuring the temperature of the hottest component and comparing it to a reference voltage.

servo-control can also be achieved by estimating the temperature of the hottest component from an easily measured temperature (typically in the regulator and by deducing said temperature of the hottest component.

example of a circuit for supplying the rotor winding of an alternator-starter has been shown in FIG. 5. This excitation circuit 1 is a voltage-raising chopper circuit which comprises an inductance LB mounted between a supply line at the positive network voltage a TB switch which is also connected to ground.

The excitation circuit 1 is therefore an electronic booster according to a characteristic of the invention. Advantageously, the boost is more important in starter mode than in alternator mode.

switch TB mounted between ground and inductance LB is mounted in parallel with a branch which comprises in series a capacitor CB and a diode DB, the anode of this diode DB being connected to the inductance LB, its cathode being connected to the capacitor CB, the capacitor CB being mounted between this diode DB and the ground. The point between the cathode of the diode DB and the capacitor CB is that which supplies the winding of the LEXC rotor.

To this end, this point is connected to said LEXC winding via a switch T2.

In addition, a switch T1 is mounted with a diode D1 between the positive supply line of the network and the ground. Diode D1 is conducting from ground to switch T1, its anode being connected to ground.

A point between the switch T1 and the diode D1 is connected to a point between the rotor winding LEXC and the switch T2 by a diode D2 which is passed from the transistor T1 towards the excitation winding of the rotor LEXC.

The assembly constituted by the transistor T1 and the diode Dl corresponds to the switching means referenced 2 in FIG. 1 (this assembly 2 can for example be a regulator designated under the terminology "high side" by the person skilled in the art and used on the machines currently).

At an opposite end to the transistor T2, the rotor winding LEXC is connected by a diode D3 to the supply line at the mains voltage. This diode D3 is passed from the rotor winding to said network voltage line.

The point common to the rotor winding and to the diode D3 is connected to earth by a TDMG switch which controls the rapid demagnetization of the rotor.

Such an arrangement allows the operation which will now be described.

In alternator mode, the T2 switch is open and the TDMG quick demagnetization switch is closed.

Regulation takes place via switch T1.

In the event that the electrical connection between the alternator and the battery is accidentally cut ("load dump"), rapid demagnetization is implemented by opening the switch T1 and the switch TDMG. current then flows through the LEXC rotor winding as shown in Figure 5.

starter mode, switch T2 is closed. the same is true for the TDMG switch.

As illustrated in FIG. 6, when the contact switch is closed, the excitation winding is advantageously supplied with a high voltage or current, for example a voltage of the order of 20 V and current of 10 A, knowing that the nominal voltage is normally 14V.

This is obtained thanks to the overexcitation circuit 1 in which the switch TB is controlled with a pulse width modulated signal (TWM according to English terminology) with a frequency of the order of 100 to 150 KHZ.

The large voltage or current thus generated makes it possible to quickly install a large starting torque.

For example, the overexcitation circuit 1 makes it possible to impose a voltage at the terminals of the rotor of 18 V instead of a voltage 8 V.

supply voltage of the rotor winding LEXC is then reduced in a second phase to be passed for example '12V or 6A at the end of a given time, which avoids excessively heating the excitation winding of the alternator-starter.

Then, the voltage becomes negative when starting is detected, so as not to overload the heat engine in the starting phase and prevent it from stalling when switching to alternator mode.

This voltage reversal is obtained for example by means of the fast demagnetization switch TDMG, which is then kept open, at the same time as the switch T1.

The TMG switch therefore makes it possible to quickly deactivate the excitation winding by stopping the current in it. Thanks to its provisions the starting torque - and therefore the power - of the alternator-starter is increased to the maximum. The rotor is therefore magnetized with a current flowing in the excitation winding greater than that required in alternator mode.

now refers to FIG. 7 in which another possible embodiment of the invention has been illustrated. In this embodiment, the overexcitation circuit 1 is identical to that described with reference to FIG. 5, except that the switch T2 is mounted between the inductance LB and the supply line.

The point common to the capacitor CB and to the diode DB is directly connected to the LEXC excitation winding.

At its opposite end, this LEXC excitation winding is connected to ground by the switch T1 to the supply line by the diode Dl, which is passed from said LEXC excitation winding to the positive supply line.

operation of such a circuit is as follows.

alternator mode, the TB switch open, while the T2 switch is closed.

supply of the winding of the rotor LEXC is regulated by the switch Tl, which is controlled for example by a voltage "PWM", by means of a commercial regulator designated under the terminology "low side" by the person skilled in the art.

In starter mode, the switches T1 and T2 are closed.

The overexcitation of the LEXC winding is controlled by the TB switch and in particular by the duty cycle of the signal which opens and closes this switch.

When it is desired to reverse the voltage at the terminals of the excitation winding LEC, in particular at the end of the start-up period or to achieve rapid demagnetization, the three switches T1, T2 and TB are opened.

The fast demagnetization current then flows as indicated in FIG. 7 and in particular through the diode which is mounted in parallel with the transistor TB and which can be the intrinsic diode of a MOSFET transistor.

Reference is now made to FIG. 8. The circuit shown in this figure a circuit with step-down or “buck-boost” mounting according to the terminology of a person skilled in the art.

I1 comprises an inductor LB mounted between the positive supply line and ground, a diode mounted between the end of said inductor LB which is opposite to ground and a capacitor CB which is connected to ground at its end opposite to said DB diode.

The point common to the diode DB and to the capacitor CB is connected negative potential of the rotor winding LEXC, the opposite end of said winding being connected by a switch TDMG to the earth of the on-board network.

switch T1 is mounted between the point common to the inductance LB and the diode DB and a supply terminal at the battery voltage.

TDMG fast demagnetization switch is a MOSFET transistor. A Zener DZ diode is mounted between the gate of said transistor and its drain (the earth of the on-board network), while being conducting in Zener mode from ground to the gate.

operation of such an assembly is as follows.

In alternator mode and in starter mode, the TDMG switch is closed and the machine is regulated by switch T1. The demagnetization voltage is obtained by opening the switch T1 and by opening the switch TDMG. The TDMG switch then operates in linear mode with a source drain voltage equal to the Zener voltage.

The rotor winding then discharges as illustrated in FIG. 8, the potential of the point common to the capacitor CB and the diode DB becoming just above ground.

Finally, we refer to Figure 9.

The assembly which is represented in this figure is identical to that of FIG. 8, except that the switch TDMG is not mounted between the rotor winding LEXC and the ground, but between the inductance LB and the ground.

The operation of such an arrangement is as follows. In alternator mode, the switch TDMG is closed and the supply of the rotor winding LEXC is controlled by the switch Tl.

In starter mode, regulation is done through switch T1, the TDMG switch being closed.

To reverse the voltage across the rotor winding, in particular where a "load dump" is detected or at the end of the start-up period, as illustrated in FIG. 6, the TDMG switch is opened at the same time time as the switch Tl, so that the excitation coil discharges quickly into the on-board network.

Of course overexcitation of the excitation winding can be achieved in another way. For example, one can act on the number of turns of the excitation coil of the rotor and on its resistance in order to obtain a higher number of amperes on the same supply voltage. For example, by considering an excitation winding of a rotor of a conventional alternator comprising N turns of section A corresponding to a resistor R, one embodiment of the invention consists in providing this excitation winding with N / 2 turns of section 2A which corresponds to a resistance R / 4.

The current therefore becomes 4 times higher than that of the conventional alternator for the same voltage. The number of ampere turns is twice that of the conventional alternator.

Figures 10 and 11 described below illustrate embodiments of the overexcitation circuit.

As a variant, the voltage can be increased in starter mode using a booster as mentioned above. For example, a voltage close to 1.5 times the nominal voltage can be applied using an electronic booster, ie with a current of 1.5 times the nominal current in alternator mode.

This boost leads to an increase in the electric current flowing through the excitation coil. In operating phases in alternator mode excitation voltage is then reduced to a value allowing satisfactory operation for the load balance.

For example, when the overexcitation circuit includes a command above with a pulse width modulation PWM signal, one can act on the excitation duty cycle to decrease it in alternator mode in order to have an electric power to dissipate in the excitation coil equivalent to that of a conventional coil.

Overexcitation can only occur in starter mode.

Advantageously, an overexcitation is also produced in alternator mode which allows more power for consumers and / or loads for a nominal voltage of 14V with a 12V battery without the need for a more powerful battery, knowing that vehicles automobiles are more equipped with equipment requiring more energy.

In starter mode (operation with an electric motor), the over-excited alternator-starter can cause more consumers and / or loads, especially when the vehicle engine is stopped at red light, the alternator-starter then operating as an auxiliary engine.

Thanks to the overexcitation the starting torque can be produced more quickly and can increase and decrease more easily thanks in particular to the rapid demagnetization.

Overexcitation can be achieved with an excitation winding of lower resistance compared to that of a conventional alternator.

Thus in the circuit of FIG. 10, two switches T1, T2 are provided, here in the form of transistors, a fast demagnetization diode DDMG, a freewheeling diode DRL.

In starter mode the switches T1 and T2 are closed so that the excitation winding LEXC is supplied, the diodes DRL and DDMG not driving. More precisely, the switch T1 is mounted between the supply line B + of the battery and the input of the winding LEXC, while the switch is mounted between the output of the winding LEXC and the ground.

The demagnetization DDMG diode is mounted between the input of the LEXC coil and the earth on the side of its anode, in parallel with the switch T2. The DRL diode is mounted between the B + terminal on the cathode side and the output of the LEXC coil.

As a result, rapid demagnetization is obtained when the switches T1 and are open, the diodes DRL and DDMG then being conductive.

In alternator mode the switch Tl is closed and the switch T2 switches to have a variable duty cycle as a function of the state of charge and / or of additional charges.

This duty cycle varies between a maximum duty cycle and lower duty cycles.

The circuit in figure can be replaced by that in figure 11 with diodes mounted in parallel with switches T1 and T2.

The LEXC winding at its output connected directly to ground and its input connected to terminal B + via the transistor Tl mounted in parallel with the diode D1 whose cathode is connected to the supply terminal B +.

The LEXC winding input is also connected to ground via a circuit comprising a diode D3, the anode of which is mounted in series with the switch T2 mounted in parallel with the diode D2 connected to ground on the side of its cathode.

In starter mode the switch T1 is closed or is the subject of a PWM voltage. Switch T3 is open.

In alternator mode the switch T1 is subjected to a PWM type regulation voltage and the switch T2 is closed.

Rapid demagnetization is carried out by blocking the transistors T1 and T2. In all the figures, rapid demagnetization avoids unnecessarily taking torque from the heat engine at the start of operation in alternator mode.

The engine will not stall at the start of its start-up - at idle speed - because at this time the excitation coil is not activated. The magnetization of the excitation coil in alternator mode is done once the engine is started. This demagnetization is used in the event of a Load dump.

Of course once the starting torque is installed quickly, other forms of curves can be produced, as shown in dotted lines in FIG. 6. The dotted curve allows a gradual reduction.

Also shown in this curve is the operation in alternator mode, no unnecessary torque being taken thanks to the rapid demagnetization.

After starting, switching to alternator mode can be done in a known manner with a progressive charge, or a speed control to avoid stalling of the vehicle's thermal engine.

As a variant, of course, the control in alternator mode can be achieved with an open loop.

It is therefore possible not to use a temperature control in alternator mode.

The alternator flow curve (intensity as a function of the number of revolutions per minute) is in one embodiment programmed using thresholds of cyclic ratios of signals with modulation of pulse widths fixed in advance and corresponding to the motor vehicle needs.

This programming reduces, for example, the intensity at high speeds of rotation and at high flow rates, for example of the order of 90 to 120 amps to avoid using excessively expensive bearings for supporting the rotor shaft. For economic reasons, we can therefore be penalized at high rotational speeds. In the low speed ranges, an overexcitation is carried out. It is the same in the medium speed range, around 3000 revolutions per minute, an overexcitation is carried out, the current delivered then being of the order of 60 to 90 amperes.

As best seen in Figure 12 above the neighboring point, the flow is reduced, the theoretical curve being shown in dotted lines. This is pre-programmed in advance, in particular according to the tests, point no depending on applications. With a temperature control, the same curve is obtained.

The excitation winding can be overexcited by varying the number of amperes turns of said winding. Of course it is possible, in alternator mode, to produce an overexcitation in the high speeds of rotation of the rotor thanks to the control of the above-mentioned parameter.

As a variant, the excitation winding can be shaped using a shaping tool to give the latter at its outer periphery a pointed shape or a barrel shape so that the winding comes as close as possible to the axial teeth. of the claw rotor as described for example in document FR00 06853 filed on May 29, 2000. This is favorable for overexcitation.

Of course the alternator-starter can be installed at the clutch of the motor vehicle as described for example in document FR-A-2 782 356 filed on July 28 1 Thus the rotor of the alternator-starter can be installed between the internal combustion engine of the motor vehicle and the reaction plate of the friction clutch.

The rotor can be carried by the drive wheel in rotation of the friction clutch, the reaction plate then constituting the rear end of the drive wheel.

The alternator-starter can be brushless. As a variant, the alternator-starter comprises a rotor with salient poles with excitation windings associated with each pole.

Claims (12)

<U> CLAIMS </U> 1. Device for supplying the winding of a rotor of an alternator-starter of a vehicle, in particular an automobile, suitable for operating as an electric generator in an alternator mode and for operating as an engine in a starter mode, characterized in that comprises means for overexciting the rotor winding to maximize the starting torque of the alternator-starter. 2. Device according to claim 1, characterized in that the rotor supply means consists of a voltage booster circuit. 3. Device according to claim 1, characterized in that the first means for supplying the rotor consists of a rotor winding having a low resistance in order to obtain, under the same supply voltage, a higher number of ampere turns. 4. Device according to any one of the preceding claims, characterized in that it includes a fast demagnetization circuit, to avoid stalling of the heat engine during the transition from the start function to the alternator function, and to protect, in mode alternator, clipping diodes against high energy overvoltages produced during load-dump. 5. Device according to any one of claims 1 to 4 characterized in that it comprises an inductor mounted between a point for the voltage supply of said device and a switch which is also connected to ground, a branch mounted in parallel to said switch and which comprises in series a capacitor (CB) and a diode (DB), the anode this diode (DB) being connected to the inductor (LB), its cathode being connected to the capacitor (CB), the capacitor (CB) being mounted between this diode DB) and the ground, a point between the cathode of the diode (DB) the capacitor (CB) being connected to said winding (LEXC) by means of a switch (T2), a switch (T1) being mounted with a diode (D1) between the positive supply line of the network and the ground, the diode (Dl) passing from ground to the switch (Tl), its anode being connected to ground, a point between the switch (Tl) the diode (D1) being connected to a point between the rotor winding LEXC and the switch (T2) by a diode (D2) which goes from the switch (T1) towards the rotor winding (LEXC), rotor winding (LEXC) being connected by a diode ( D3) the power supply to the on-board network, this diode (D3) passing from the rotor winding to said network voltage line, the point common to the rotor winding and to the diode (D3 being connected to ground by a switch ( TDMG) which controls rapid demagnetization. 6. Device according to any one of claims 1 to 4 characterized in that it comprises an inductor mounted between a switch (T2) connected to a point for supplying voltage to said device and a switch (TB) which is by elsewhere connected to ground, a branch mounted in parallel to said switch which comprises in series a capacitor (CB) and a diode (DB), the anode of this diode (DB) being connected to the inductor (LB), its cathode being connected to the capacitor (CB) the capacitor (CB) being mounted between this diode (DB) and the ground, the point common to said diode (DB) and to the capacitor (CB) being connected to said winding (LEXC), a switch (T1 ) being mounted with a diode (D1) between the positive supply line of the network and the ground, the diode (D1) passing from the ground to the switch (T1), its anode being connected to ground, a point between the switch (Tl) and the diode (D1) being connected to the end of the coil rotor ge (LEXC) opposite inductance (LB). 7. Device according to any one of claims 1 to 4 characterized in that it comprises an inductor (LB) mounted between the positive supply line and the ground, a diode (DB) mounted between the end of said inductor (LB) which is opposite to ground and a capacitor (CB) which is connected to ground at its end opposite to said diode (DB), the point common to the diode (DB) and to the capacitor (CB) being connected to negative potential of the rotor winding (LEXC), the opposite end of said winding being connected by switch (TDMG) to the earth of the on-board network, a switch (T1) being mounted between the common point with 1 inductance (LB ) and to the diode (DB) and a power supply terminal at the battery voltage, the switch (TDMG) connected to the rotor winding being a MOSFET transistor, a Zener diode (being mounted between the gate of said transistor and its drain connected to the earth of the on-board network), being Passing in Zener mode from the mass to the grid. 8. Device according to any one of claims 1 to 4 characterized in that it comprises an inductor (LB) mounted between the positive supply line and the ground, a diode (DB) mounted between the end of said inductor (LB) which is opposite to ground and a capacitor (CB) which is connected to ground at its end opposite to said diode (DB), the point common to the diode (DB) and to the capacitor (CB) being connected to negative potential of the rotor winding (LEXC), the opposite end of said winding being connected to the on-board network ground, a switch (T1) being mounted between the point common to the inductor (LB) and to the diode (DB) and a battery voltage supply terminal. 9. Device according to any one of claim to 4, characterized in that it comprises a switch (T1) mounted between the input of the excitation winding (LEXC) and the supply line (B +) of the battery, a switch (T2) mounted between earth and the winding output (LEXC), a demagnetization diode (DDMG), mounted between the input of the excitation coil (LEXC) and earth, the anode of the diode (DDMG) being connected to ground, and a diode (DRL) mounted between the terminal (B +) and the output of the excitation coil (LEXC), the cathode of the diode (DRL) being connected to the line of food (B +). 10. Device according to any one of claims 1 to 4 characterized in that it comprises an excitation coil (LEXC) having its output connected to ground, and its input connected to the supply terminal (B +) via a transistor ) mounted in parallel with the diode (Dl) including the cathode connected to the power supply terminal (B +), the input of the excitation winding (LEXC) connected to ground via a diode (D3) connected in series with a switch ( T2) on the side of its anode, said transistor (T2) being mounted in parallel with a diode, the cathode of which is connected to ground. 11. Method for controlling the supply of a rotor winding of a starter or alternator starter of a vehicle, in particular an automobile, characterized in that said winding is overexcited for a first period after the closure of the vehicle contact switch and in that the voltage level is reduced after a given period before starting the vehicle's heat engine. 12. The method of claim 11, for controlling the supply of a rotor winding of an alternator-starter, characterized in that the excitation voltage is reversed for a given period when the vehicle's engine starts. is detected.