Abstract:
A synchronous rectification alternator for a motor vehicle is disclosed. The alternator includes a stator, a rotor, and a synchronous rectification system for rectifying into a DC voltage the alternating voltages supplied by the stator, and a voltage regulator for regulating the DC voltage. The alternator also includes fault detection for detecting faults in the synchronous rectification and supplying fault detection information to the voltage regulator. In one version, the fault information is supplied to the voltage regulator at fault inputs also receiving phase signals representing the alternating voltages supplied by the stator. At least one of the items of fault information is used to cause, in the voltage regulator, opening of an excitation circuit supplying current to an excitation coil of the rotor so as to produce, in the voltage regulator, a fault indication. The opening of the excitation circuit is preferably caused through a suitable command of a fast demagnetization transistor included in the excitation circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application relates to International Application No. PCT/FR2010/051554 filed Jul. 22, 2010 and French Patent Application No. 09/56067 filed Sep. 7, 2009, of which the disclosures are incorporated herein by reference and to which priority is claimed. 
     FIELD OF THE INVENTION 
     The present invention concerns in general terms the field of rotary electrical machines, in particular for motor vehicles. More particularly, the invention concerns an alternator with synchronous rectification equipped with electronic fault management means. 
     BACKGROUND OF THE INVENTION 
     In the context of reducing CO 2  emissions and developing high-efficiency alternators, the synchronous rectification technology applied to alternators for motor vehicles has a certain interest. 
     Synchronous rectification uses a bridge rectifier with power transistors, generally of the MOSFET type. Control electronics are also provided for shaping suitable control signals for the power transistors. 
     Compared with conventional alternator technology with a diode bridge rectifier, the proportion of electronics in synchronous rectification machines is increasing significantly. 
     In terms of cost, the proportion of electronics in a synchronous rectification machine may be between 30% and 50% of the total cost of the machine. By way of comparison, the proportion of the cost of the electronics in diode bridge rectification machines is around 25%. A breakdown in the electronics requiring a replacement of the faulty part may therefore give rise to appreciable cost repercussions in after-sales service operations. 
     Reliability of the electronics is essential for the overall reliability of the machine and gives rise to novel constraints for the designers. These constraints are all the more severe since the current trend in motor manufacturers is to extend the guarantee period for the vehicles. 
     It is therefore desirable to propose solutions affording an improvement in the overall reliability of a synchronous rectification alternator and, more particularly, the reliability of the electronics in such a alternator. 
     SUMMARY OF THE INVENTION 
     According to a first aspect, the invention concerns a synchronous rectification alternator for a motor vehicle, comprising a stator, a rotor, synchronous rectification means for rectifying into a DC voltage the alternating voltages supplied by the stator, and voltage regulation means for regulating the DC voltage. 
     In accordance with the invention, the alternator also comprises fault detection means for detecting faults in the synchronous rectification means and supplying fault detection information to the voltage regulation means. 
     According to a particular feature, the fault information is supplied to the voltage regulation means at fault inputs also receiving phase signals representing the alternating voltages supplied by the stator. 
     According to another particular feature, at least one of the items of fault information is used to cause, in the voltage regulation means, opening of an excitation circuit supplying current to an excitation coil of the rotor so as to produce, in the voltage regulation means, a fault indication corresponding to the said at least one of the fault information items. Preferably, the opening of the excitation circuit is caused through a suitable command of a fast demagnetisation transistor included in the excitation circuit. 
     According to yet another particular feature, the fault detection means comprise means for detecting faults occurring in arms of a transistor bridge rectifier of the synchronous rectification means, the detection being performed using phase signals taken at mid-points of the arms, control signals applied to control electrodes of the transistors and voltages present on the positive and negative voltage terminals of the alternator. 
     According to yet another particular feature, the fault detection means comprise means for detecting overheating faults occurring in arms of the transistor bridge rectifier of the synchronous rectification means. 
     According to a particular embodiment, the fault detection means comprise means for detecting a faulty connection of a battery of the motor vehicle to an electrical supply network to which the alternator is also connected when the latter is installed in the vehicle, the detection being performed using a measurement of voltage appearing between the positive and negative voltage terminals of the alternator. In addition, in this embodiment, a detection of a faulty connection of the battery is effective when a negative voltage of between −1 volt and −2 volts is measured between the positive and negative voltage terminals of the alternator. 
     According to another particular feature, the alternator comprises means for protecting the alternator when a faulty connection of the battery is detected by the fault detection means. The protection means may for example comprise a charge pump circuit and/or a photovoltaic isolator. 
     According to yet another particular feature, the fault detection means also comprise means for storing information on faults detected and/or transmitting these to an electronic control unit of the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects, aims and advantages of the present invention will emerge more clearly from a reading of the following detailed description of a particular embodiment thereof, given by way of non-limitative example and made with reference to the accompanying drawings, in which: 
         FIG. 1  is a general block diagram of an embodiment of the alternator according to the invention; 
         FIG. 2  is a simplified diagram of a transistor bridge rectifier included in the alternator in  FIG. 1 ; 
         FIG. 3  shows block diagrams of a bridge rectifier control circuit and a fault protection and transmission circuit included in the alternator in  FIG. 1 ; and 
         FIG. 4  shows a particular embodiment of a protection circuit included in the alternator in  FIG. 1 , provided for protecting the alternator against a vehicle battery connection reversal. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , the alternator according to the invention comprises a rotary electrical machine  1 , a voltage rectification circuit  2  and a voltage regulator  3 . 
     In this embodiment, the machine  1  is a three-phase machine of the Lundell type and comprises, in a conventional manner, a stator S and a claw rotor R comprising an excitation coil. The rotor R is rotated by means of a transmission belt connecting it to the crankshaft of the thermal engine  5  of the vehicle. 
     The voltage rectification circuit  2  is of the synchronous rectification type and comprises a voltage rectification bridge  20 , a bridge control circuit  21  and a fault protection and transmission circuit  22 . 
     As shown in  FIG. 2 , the voltage rectification bridge  20  is a MOSFET transistor bridge. First, second and third bridge arms  201 ,  202  and  203  are each formed from two MOSFET transistors  201 H and  201 L,  202 H and  202 L, and  203 H and  203 L, respectively. The transistors in the same arm have first power electrodes (drain, source) connected together at an arm mid-point and second power electrodes (drain, source) connected respectively to voltage terminals B+ and B− of the alternator. The B+ terminal conventionally delivers the +12 V voltage of the vehicle supply network. The B− terminal is connected to the earth of this same voltage supply network. 
     Three phase voltages φ 1 , φ 2  and φ 3  supplied by the machine  1  are applied respectively to the three mid-points of the bridge arms  201 ,  202  and  203  of the rectification bridge  20  between the two MOSFET transistors  201 H and  201 L,  202 H and  202 L, and  203 H and  203 L, respectively, and supply these bridge arms  201 ,  202  and  203 . 
     Control electrodes (gates) of the transistors  201 H and  201 L,  202 H and  202 L, and  203 H and  203 L, receive respectively gate control signals CG 1 H and CG 1 L, CG 2 H and CG 2 L, and CG 3 H and CG 3 L. These signals CG 1 , CG 2  and CG 3  control the transistors so as to make them function as synchronous rectifiers. 
     The bridge control circuit  21  is shown in detail in  FIG. 3 . This circuit  21  comprises a circuit  210  for shaping gate control signals and a fault detection circuit  211 . 
     The circuit  210  for shaping gate control signals performs a suitable shaping of the signals CG 1 , CG 2  and CG 3  so as to obtain a synchronous-rectification functioning of the MOSFET transistors of the bridge  20 . This type of synchronous-rectification functioning of MOSFET transistors is known to persons skilled in the art and will not be described here. 
     The function of the fault detection circuit  211  is essentially to detect faults in the voltage rectification bridge  20 . However, certain faults in the stator windings of the stator S could, in certain embodiments of the invention, also be detected by this circuit  211  because of the information contained in the signals supplied to the circuit  211 . 
     In this embodiment, the fault detection circuit  211  receives as an input the gate control signals CG 1 , CG 2  and CG 3 , the phase voltages φ 1 , φ 2  and φ 3 , the voltages of the terminals B+ and B− and temperature information Temp supplied for example by a temperature sensor (not shown). From the values of these various signals that are compared with thresholds and an associated logic processing, the fault detection circuit  211  is capable of detecting a reversal of the connection of the vehicle battery terminals (referred to as “reverse battery” in English terminology), overheating of the bridge  20  and any failures of the MOSFET transistors. 
     The fault or faults detected are here coded in the fault detection circuit  211  before being transmitted to the fault protection and transmission circuit  22  by the circuit  211 . For example, a two-bit binary fault word DEF is provided for indicating various types of fault. Four different faults DEF 1 , DEF 2 , DEF 3  and DEF 4  can thus be coded in two bits in the fault word DEF. 
     In this embodiment, the fault DEF 1  is the battery connection reversal fault and the faults DEF 2 , DEF 3  and DEF 4  are respectively the fault of overheating of the voltage rectification bridge  20 , a short-circuit fault in an arm of the bridge  20  (transistor short-circuited) and an open-circuit fault in the bridge  20 . 
     The battery connection reversal fault occurs in the case where, for one reason or another, the B+ and B− terminals of the alternator are connected not to the +12 V and 0 V terminals of the battery, but to the 0 V and +12 V terminals respectively. This normally occurs when an operator reverses the two cables of the vehicle that must be connected to the battery. 
     The inventive entity found that, in the case of a battery connection reversal fault DEF 1 , a negative voltage TIB of between −1 V and −2 V appeared between the terminals B+ and B−. The presence of this voltage TIB is detected by the fault detection circuit  211 , which consecutively deduces therefrom a battery connection reversal fault DEF 1 . 
     In accordance with this embodiment, when the battery connection reversal fault DEF 1  is detected, the occurrence of this fault is stored in an internal memory MEMdef of the fault detection circuit  211 . Such a storage of the occurrence of a battery connection reversal fault enables the manufacturer of the alternator, in certain after-sales service situations, to deny responsibility in the event of damage caused to the alternator or to the vehicle by a battery connection reversal operation. In other embodiments, all the faults appearing are stored in the internal memory MEMdef in the form for example of a fault history. 
     The fault word DEF (DEF 1 , DEF 2 , DEF 3  and DEF 4 ) is transmitted by the circuit  211  to the fault protection and transmission circuit  22 . 
     As shown in  FIG. 3 , the fault protection and transmission circuit  22  comprises a fault transmission circuit  220  and a circuit  221  for protection in the event of battery connection reversal. 
     The fault transmission circuit  220  comprises in particular a decoding circuit  2200  and a switching circuit  2201  with two transistors. The decoding circuit  2200  receives the word DEF transmitted by the fault detection circuit  211  and activates outputs S 1 , S 2 , S 3  and/or S 4  according to the decoding made of the word DEF received. 
     The output S 1  is activated when a battery connection reversal fault DEF 1  occurs. The output S 1 , when it is active, demands the activation of the protection circuit  221 . 
     The protection circuit  221  comprises a voltage source  2210  and six outputs SG 1 H, SG 1 L, SG 2 H, SG 2 L, and SG 3 H, SG 3 L that each deliver a voltage VG supplied by the voltage source when the circuit is activated by the output S 1 . 
     The six outputs SG 1 H, SG 1 L, SG 2 H, SG 2 L and SG 3 H, SG 3 L are connected respectively to the gates of the transistors  201 H,  201 L,  202 H,  202 L and  203 H,  203 L through diodes D 1  to D 6 . When the circuit  221  is activated, the voltage VG, around 6 volts in this embodiment, is applied to the gates of the transistors  201 H,  201 L,  202 H,  202 L and  203 H,  203 L so as to force these into a conduction state. 
     This arrangement affords a reduction in the power dissipated by the MOSFET transistors, so that the user has more time before the voltage rectification bridge  20  is damaged in order to become aware of his error in reversing the battery cables and eliminate the fault. 
     This is because, in the case of this battery connection reversal fault DEF 1 , the bridge  20  is subjected to a negative voltage and the antiparallel diodes of the MOSFET transistors are then conductive. The current passing through the transistors is then extremely high, around 300 A and, if no step is taken, the power to be dissipated by each transistor is approximately 300 A×0.8 V-2400 W, the voltage of 0.8 V being the direct voltage appearing at the terminals of the antiparallel diode for a current of 300 A. The silicon chip of the transistor can withstand these conditions only for a few fractions of a second. 
     In accordance with the invention, because of the application of the voltage VG on the gates of the transistors, the latter go into a conduction state, so that the power dissipated by each transistor is around (300 A) 2 ×0.002Ω=180 W, the ohmic value of 0.002 Ω corresponding to the equivalent resistance of the transistor in the conduction state thereof. A MOSFET power transistor can withstand these conditions for several seconds, which leaves time for the user to realise his error in reversing the battery cables and eliminate this fault. 
     A supply source of the protection circuit  221  making it possible to obtain the voltage VG can be implemented by means of a charge pump circuit such as the MAX  865  circuit sold under the registered trademark MAXIM. 
     In a different embodiment, it is also possible to use a photovoltaic isolator of the PVI5050N or PVI5080N type (registered trademarks), as shown by the reference  6  in  FIG. 4 . Such an isolator  6  makes it possible to detect a battery connection reversal and to apply a voltage VG to the gates of the MOSFET transistors. An emitting diode DE of the isolator  6  is connected between the terminals B+ and B− so that it becomes conductive when the negative voltage TIB (between +1 V and −2 V as indicated previously), due to the battery connection reversal, appears between these electrodes. 
     The passage of a direct current in the emitting diode DE causes the appearance of a voltage at the terminals of photovoltaic elements PV of the isolator  6 . The voltage VG is obtained from the voltage supplied by the photovoltaic elements PV. 
     The fault information DEF 1 , DEF 2 , DEF 3  and DEF 4  is transmitted to the voltage regulator  3  by the fault transmission circuit  220 . The voltage regulator  3  can thus trigger fault operating modes, activate a fault signal (indicator light) for the user of the vehicle and/or indicate the occurrence of a fault to an electronic control unit of the vehicle, such as an engine control unit  4  (shown in  FIG. 1 ), with which the regulator  3  is in communication. The outputs S 2 , S 3  and S 4  of the circuit  2200  are used for transmitting fault information DEF 1 , DEF 2 , DEF 3  and DEF 4  to the voltage regulator  3 . 
     In this embodiment, a regulator  3  is used that comprises phase fault detection inputs ed 1  and ed 2 , to which the phase signals φ 1  and φ 2  are applied. In this type of regulator, these fault inputs ed 1 , ed 2  are normally provided for detecting phase faults in the alternator  1 . It is thus possible to detect short-circuit and open-circuit phases by these means. The availability of these inputs ed 1  and ed 2  is taken advantage of in this embodiment of the invention in order to indicate to the regulator  3  faults DEF detected by the fault detection circuit  211 . 
     According to the faults to be indicated to the regulator  3 , the inputs ed 1  and ed 2  are placed at appropriate voltage levels, recognisable by the regulator  3  in order to indicate faults. The signals S 2  and S 3  force the states of the inputs ed 1  and ed 2  by means of the transistors of the switching circuit  2201  (cf.  FIG. 3 ), according to the faults to be indicated. 
     A fault management circuit  30  and rotor excitation circuit  31  included in the regulator  3  are shown in  FIG. 1 . The fault management circuit  30  is the circuit incorporating the fault inputs ed 1  and ed 2  indicated above as well as another fault input ed 3 . 
     The fault input ed 3  indicates an open-circuit fault in the excitation circuit  31  of the alternator rotor R. The rotor excitation circuit  31  comprises known means for detecting and indicating an open-circuit state. Such means detect an open circuit for example because of the presence of a zero excitation current during at least one period greater than a certain predetermined threshold period. 
     As is clear in  FIG. 1 , the rotor excitation circuit  31  comprises two transistors T PWM  and T DEMAG . The transistor T PWM  is a power transistor that controls a pulse width modulation of the excitation current supplying the excitation coil of the rotor R. The transistor T DEMAG  is a power transistor that opens the excitation circuit when it is necessary to demagnetise the alternator quickly. The two transistors T PWM  and T DEMAG  are here both transistors of the MOSFET type. 
     In accordance with the invention, the presence of the transistor T DEMAG  is here used as a means for forcing an opening of the rotor excitation circuit  31  so as to cause a fault to be fed back to the fault management circuit  30 , through the activation of the fault input ed 1 . When a fault DEF corresponding to an activation of the output S 4  of the circuit  2200  must be indicated to the regulator  3 , the gate of the transistor T DEMAG  is controlled by the output S 4  so as to cause this transistor to be switched off, thus forcing an opening of the current circuit. 
     The fault management circuit  30  processes the various items of fault information that arrive at it through the inputs ed 1 , ed 2  and ed 3  so as, depending on the application, to indicate these faults to the engine control unit  4  and/or to optionally establish suitable fault operating modes. In addition, the fault management circuit  30  can also control the activation of an indicator LAMP to indicate certain faults to the user of the vehicle. 
     In accordance with the invention, it will be arranged for the transmission of the fault information of the fault detection circuit  22  to the fault management circuit  30  of the voltage regulation circuit  3  to be able to take place by various means, as is clear from the above description, and for various types of coding to be able to be used to transmit this information. Apart from the choice of the activation of the inputs ed 1 , ed 2  and ed 3  that are activated to transmit the information, other coding parameters can also be used, such as for example distinct predetermined periods for activation of the fault inputs ed 1 , ed 2  and ed 3  in order to transmit different items of fault information. 
     Moreover, it should be noted that the various electronic control circuits that have been described here, namely the circuits  21 ,  22  and  3 , according to the various embodiments of the invention, can be implemented in the form of one or more ASICs. 
     Naturally, the invention is not limited to the particular embodiments that have just been described. Other embodiments are possible according to the applications envisaged by a person skilled in the art and remain within the scope of the accompanying claims.