Abstract:
The invention concerns a device for protecting an electric source adapted to power an electric member comprising a test unit ( 6 ) adapted to deliver a signal ( 8 ) representing the availability of the electric source ( 2 ), to a control unit ( 10 ). The unit ( 10 ) determines an operating mode of the electric member ( 4 ) wherein the power consumption of the electric member is a function of the availability signal ( 8 ) received from the test unit ( 6 ). The electric source ( 2 ) can power directly the electric member ( 4 ) and the control unit ( 10 ) can act on the electric member itself. The control unit ( 10 ) can also be interposed between the electric source ( 2 ) and the electric member ( 4 ) to modify at least one characteristic of the current powering the electric member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to the supply of electrical energy to electrical components installed on board a motor vehicle. 
   2. Background of the Related Art 
   Modern motor vehicles comprise numerous auxiliary equipments essential for the functioning of the vehicle such as pumps and fans, or which provide additional comfort and safety, like air-conditioning installations, devices to prevent the locking of brakes, known as “ABS”, safety airbags, etc. Some of these devices, like the safety airbags, can be operated only electrically. Others, such as fans and pumps, can be driven mechanically by the engine itself. But their functioning is then linked with the engine speed, which constitutes a significant disadvantage. 
   That is why these equipments are increasingly driven by the intermediary of an electric motor that is itself powered by an electrical source of the vehicle. This makes it possible to decouple the functioning of these devices from that of the engine and, for example, to make them operate even when the engine is stopped or is running at idling speed. However, this tendency to actuate equipments of the vehicle increasingly in an electrical manner imposes a heavy load on the electrical source of the vehicle. The latter can therefore get into a state of availability that is inadequate for ensuring the functioning of vital safety devices (safety airbags, ABS). For example, if the electrical energy source is an accumulator battery, its charge can be insufficient. 
   That is why the need is felt for a device capable of protecting the electrical source of a vehicle in such a way that it always remains available to ensure certain essential safety functions. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a device for protecting an electrical source capable of powering at least one electrical component, comprising a test unit capable of delivering a signal representative of the level of availability of the electrical source to a control unit, this control unit determining an operating mode of the electrical component in which the consumption of electrical energy of the latter depends on the availability signal received from the control unit. 
   The electrical component can be a motor driving a compressor or a cooling pump of the engine. It can also be a fan motor, a resistive element with a positive temperature coefficient or even a catalytic converter. The electrical source will most often consist of an accumulator battery, but it can also be an alternator or a fuel cell. 
   The control unit determines the state of availability of the electrical source. For example, if this source is a battery, the control unit determines its state of charge. On the basis of this information, the control unit establishes an operating mode of the electrical component chosen from among several possibilities. For example, if the availability state of the electrical source is higher than an upper threshold, the electrical component will operate at full power or will at least be able to operate at this power. If the availability of the electrical source is between an upper threshold and a lower threshold, the electrical component will have a degraded operating mode in which it will operate at only a portion of its power. Finally, if the availability state of the electrical source is below a lower threshold, the control unit will, purely and simply, stop the operation of the electrical component. 
   Thus, in the degraded operating mode, the electrical source supplies only a portion of the total power of the electrical component and when its availability state is below the lower threshold, it does not supply any energy to the electrical component. The electrical source is therefore protected and remains available for operating, in the case of need, components essential for the safety of the vehicle. 
   According to a first embodiment, the electrical source powers the electrical component directly and the control unit acts on the electrical component itself in such a way as to determine the quantity of electrical energy that the latter requests from the electrical source for its operation. This embodiment applies advantageously in the case where the electrical component is a resistive component, such as a resistive element with a positive temperature coefficient used for heating the passenger compartment of the vehicle. In the degraded mode of operation, the control unit will be able to modify the connection of this resistive element in such a way that it absorbs no more than a limited electric current and, when the availability of the source is below the value of the lower threshold, the control unit will cut off the power supply to this resistive element. 
   According to another embodiment, the control unit is interposed between the electrical source and the electrical component, and the control unit modifies, to a greater or lesser degree, a characteristic of the electric current which supplies the electrical component in such a way as to limit the quantity of energy supplied to the electrical component by the electrical source. 
   This embodiment applies advantageously in the case where the electrical component is a motor whose speed of rotation can be varied by changing the frequency of the current supplying it. If the frequency of the current reduces, the speed of rotation of the motor also reduces and, consequently, the electrical power absorbed is lower. 
   In one embodiment, the control unit consists of an inverter, capable of applying a variable frequency to the electrical component, and of a control circuit of the inverter, this circuit comprising an assembly of resistors interposed between a ground terminal and a maximum voltage terminal of the inverter, the assembly of resistors having a plurality of connection terminals capable of being connected to an intermediate terminal of the inverter via a control line provided with adjustment means, the availability signal delivered by the test unit being supplied to the adjustment means such that it connects the intermediate terminal of the inverter to a connection terminal of the assembly of resistors determined according to the availability signal. 
   In a variant embodiment, the assembly of resistors consists of a divider bridge that comprises a plurality of resistors determining connection terminals between them and at their ends, the adjustment means connecting the control line to one of these connection terminals according to the availability signal. 
   In another embodiment, the assembly of resistors can consist of a single resistor, forming a potentiometer, and comprising a single connection terminal that can be moved in a continuous manner from one end to the other of the single resistor. 
   In a particular embodiment, the divider bridge comprises two resistors determining between them a node, the control unit consisting of a first switch having a normal operating position in which the control line is connected directly or by the intermediary of a protective resistor to the maximum voltage terminal of the inverter in order to allow a normal operating mode of the electrical component, and a degraded operation position in which the control line is connected to the node of the divider bridge in order to allow a degraded operating mode of the electrical component, and by a second switch having a closed position in which the control line is connected to the ground terminal of the inverter in order to prohibit the operation of the electrical component. 
   Advantageously, the assembly of resistors comprises a potentiometer having its end terminals directly or indirectly connected to the maximum voltage terminal and to the ground terminal of the inverter, and a slider terminal connected to the intermediate terminal of the inverter by the intermediary of the first switch when the latter is in its closed position, the device furthermore comprising a manual control adjustable by an operator and capable of controlling the potentiometer directly or indirectly. 
   The two resistors of the divider bridge can be separate from the potentiometer, or the potentiometer can constitute one of the two resistors of the divider bridge. 
   This embodiment applies advantageously in the case where the electrical component is a component that can be controlled manually by a passenger of the vehicle. If the control unit has determined that the electrical source was in an availability state that was sufficient for its normal operation to be possible (availability above the upper threshold), the driver of the vehicle or his passengers can adjust the functioning of the electrical component as they wish, for example a motor driving the compressor of an air-conditioning system. 
   The electrical component can, in particular, be an electric motor driving a compressor of an air-conditioning system and the manual control is capable of obtaining a continuous adjustment of the speed of the motor between a minimum speed corresponding to a “warmest” mode and a maximum speed corresponding to a “coolest” mode, when the device is in the normal operating mode. 
   Other features and advantages of the present invention will furthermore appear on reading the following description referring to the appended figures. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a block diagram of a first embodiment of the invention in which the control unit controls the operation of the electrical component itself; 
       FIG. 2  is a block diagram of a second embodiment of the invention in which the control unit is interposed between the electrical source and the electrical component; 
       FIG. 3  is a block diagram of the control unit comprising an inverter capable of applying a variable frequency to an electrical component constituted by a synchronous motor; 
       FIG. 4  is diagram of a particular embodiment in which the control circuit of the inverter comprises two separate switches; and 
       FIG. 5  is a diagram of an assembly of resistors comprising a manual control which can be operated by an operator. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , the reference  2  denotes an electrical source such as an accumulator battery or even an alternator or a fuel cell. The electrical source  2  supplies an electrical component  4  such as a motor driving a fan, a pump, a compressor of an air-conditioning system or even a catalytic converter or a resistive element with a positive temperature coefficient (PTC). A test unit  6  determines the availability of the electrical source  2 , in other words its capability of supplying electrical energy to the electrical component  4 . For example, if the electrical source is an accumulator battery, as is frequently the case, the test unit determines the charge of that accumulator. 
   The test unit  6  transmits an availability signal  8  depending on the availability of the source  2 . The signal  8  is applied to a control unit  10  which determines an operating mode of the electrical component adapted to the availability state of the electrical source. If the electrical source is a battery, the control unit  10  determines the charge level C of the battery. This charge level is for example expressed as a percentage of the maximum charge. Depending on this charge level, the control unit  10  determines, for the electrical component  4 , an operating mode chosen from among several possible ones, for example at least two operating modes, a normal operating mode and a degraded operating mode. Between the maximum charge level C max  and a first charge level C 1 , less than or equal to C max , the control unit  10  establishes a normal operating mode of the electrical component  10 , in other words an operating mode in which the electrical component can operate at full power. When the charge level of the battery  2  is between C 1  and a second charge level C 2 , lower than C 1 , the control unit  10  establishes a degraded operating mode of the electrical component  4  or stops the latter purely and simply. 
   In the embodiment shown in  FIG. 1 , the electrical source supplies the electrical component  4  directly and the control unit  10  modifies the configuration of the electrical component in such a way as to limit the quantity of electrical energy that the latter requires from the electrical source  2  for its operation in the degraded operating mode. For example, if the electrical component consists of electrical resistors, the interconnections of these resistors will be modified in such a way that the electrical power called upon reduces. 
     FIG. 2  shows a second embodiment of the invention. It differs from the embodiment shown in  FIG. 1  in that the control unit  10  is interposed between the electrical source  2  and the electrical component  4 . Whereas, in the embodiment shown in  FIG. 1 , the current from the electrical source  2  is supplied directly to the electrical component  4 , in the embodiment shown in  FIG. 2 , the current from the electrical source  2  is supplied to the control unit  10  and the latter modifies at least one characteristic of this current, such as its voltage or its current value, before transmitting it to the electrical component  4 . If the electrical source  2  is a battery which delivers direct current, the control unit  10  can convert this direct current into an alternating current of variable frequency. 
   This embodiment applies particularly in the case where the electrical component  4  comprises a synchronous electric motor whose speed of rotation is set according to the frequency of the electrical current supplied to it. As in the preceding embodiment, the control unit  10  can thus determine an operating mode of the electrical component  4  from among a plurality of possibilities, for example a normal operation mode, a degraded operating mode in which the electrical component operates at a portion of its power and a stopped mode. The operating mode of the electrical component is determined, as described above, according to the availability signal  8  supplied by the test unit  6  to the control unit  10 . 
     FIG. 3  shows a particular embodiment of a control unit  10  able to be used in a control device of the invention as shown in  FIG. 2 . The control device comprises an inverter  12  capable of applying an electrical current of variable frequency to an electrical component consisting of a three-phase electric motor  4  of the synchronous type. The inverter  12  has three outputs  14  connected to the motor  4  by three lines  16  respectively corresponding to the three phases of the three-phase current. The inverter  12  is connected to an electrical power supply source  2 , such as a high-power battery or an alternator set capable of delivering a DC voltage Uht. 
   The inverter  12  is controlled by a control circuit given the general reference  20 . The inverter comprises three terminals: a ground terminal  22  corresponding to a zero voltage (U=0 volt), a maximum voltage terminal  24  corresponding to a maximum voltage (U=U max ) generated by the inverter, and an intermediate terminal  26 , called the slider terminal, corresponding to a variable voltage (U=U var ), of between 0 volt and U max . 
   In the example, the maximum voltage U max  is 5 volts and the supply frequency of the motor can vary from 0 Hertz, for the voltage U=0, up to 150 Hertz for the voltage U max =5 volts. 
   The control circuit  20  also comprises an assembly of resistors, given the overall general reference  28 , interposed between the ground terminal  22  and the maximum voltage terminal  24  of the inverter  12 . For this purpose, the assembly of resistors comprises a first end terminal  32  connected to the maximum voltage terminal by a line  38  on which there is interposed a protective resistor  40 , and a second end terminal  36  connected by a line  42  to the ground terminal  22  of the inverter. 
   The assembly of resistors  28  consists of several resistors, three in the embodiment shown, that is to say the resistors  44 ,  46  and  48 . The resistors  44  and  46  determine between themselves a connection terminal  50 , whilst the resistors  46  and  48  determine between themselves a connection terminal  52 . In total, the assembly of resistors  28 , consisting of three resistors, therefore has four connection terminals, counting the two end terminals  32  and  36 . Finally the control circuit  20  comprises adjustment means  60 . 
   The availability signal of the electrical source  2  transmitted by the test unit  6  is applied to the adjustment means  60 . These adjustment means are connected to the intermediate terminal  26  of the inverter  12  by a control line  62 . The adjustment means  60  determine to which connection terminal of the assembly of resistors  8  the control line  62  will be connected. These control means can therefore determine, in the example of embodiment shown, four operating modes of the electric motor  4 . When the control line  62  is connected to the connection terminal  32 , the frequency of the electrical current supplied to the motor is maximal, which corresponds to the normal operating mode. When the control line  62  is connected to the connection terminal  40 , the resistor  44  on the one hand and the resistors  46  and  48  on the other hand constitute a divider bridge which limits the voltage applied to the intermediate terminal  26  of the inverter. The frequency of the electric current supplied to the motor is therefore reduced, which corresponds to a degraded operating mode. If the control line  62  is connected to the connection terminal  52 , the situation is identical, but the control voltage of the inverter is lower and the frequency of the current will also be lower. This operating mode therefore corresponds to a second degraded operating mode in which the protection of the electrical source is greater than in the previous case. Finally, when the control line  62  is connected to the connection terminal  36 , the stopping of the motor  4  is commanded by the grounding of the intermediate terminal of the inverter. The electrical source  2 , which no longer supplies any current, is then fully protected. 
     FIG. 4  shows a particular embodiment of a device for protecting an electrical source according to the invention. In this embodiment, the assembly of resistors  28  consists of only two resistors, namely the resistors  44  and  46 , which determine between themselves a single connection terminal  50 . The assembly of resistors  28  therefore comprises three connection terminals in total, the two end terminals  32  and  36  and the terminal  50  contained between the resistors  44  and  46 . 
   The adjustment means, denoted by the general reference  60 , consist of two separate switches, namely a first switch  70  and a second switch  72 . The switch  70  has two positions. In a first position (position I or the closed position), the control line  62  is connected to the connection terminal  32 , that is itself connected, possibly by the intermediary of a protective resistor  40 , to the maximum voltage terminal  24  of the inverter  12 . This allows a normal operating mode in which the speed of rotation is maximal. 
   In a second position (position II), the control line  62  is connected to the connection terminal  50  located between the resistors  44  and  46 . As explained above with reference to  FIG. 3 , the assembly of resistors  28  acts as a divider bridge which limits the voltage applied to the intermediate terminal  26  of the inverter, which commands a degraded operating mode of the motor. 
   The second switch  72  is fitted in a line  74  connecting the control line  62  and the line  42 . When the switch  72  is in its open position, as shown in  FIG. 4 , it is the switch  70  that determines the normal or degraded operating mode of the motor. On the contrary, when the switch  72  is in its closed position, the intermediate terminal  26  of the inverter is connected to the ground terminal  22  and the voltage applied to the terminal  26  is zero. This commands the stoppage of the motor. The switch  70  is controlled by a first sensor  80  and the second switch  72  is controlled by a second sensor  82  forming part of the test unit  6 . In other words, this embodiment is characterized by the fact that the adjustment means  60  consist of two separate switches, each one controlled by a separate signal  8 . 
   The three operating modes are summarized in the following table. 
   
     
       
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               C &lt; 40% 
               40% &lt; C &lt; 60% 
               60% &lt; C 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Switch 
               0 volt 
                0 volt 
               12 volts 
             
             
                 
               wire 70 
             
             
                 
               Switch 
               0 volt 
               12 volts 
               12 volts 
             
             
                 
               wire 72 
             
             
                 
               Switch 70 
               Position II (or 
               Position II 
               Position I 
             
             
                 
                 
               immaterial) 
             
             
                 
               Switch 72 
               Closed 
               Open 
               Open 
             
             
                 
               Mode 
               Stopped 
               Degraded 
               Normal 
             
             
                 
                 
             
           
        
       
     
   
   In the example embodiments shown in  FIGS. 3 and 4 , the operating mode of the motor is determined automatically, and exclusively on the basis of the availability of the electrical source  2 . An operator cannot adjust the speed of rotation of this motor. 
     FIG. 5  shows a variant embodiment which comprises adjustment means accessible to an operator. This embodiment is similar to the one shown in  FIG. 4  but the resistor  44 , instead of having a fixed value, has been replaced by a potentiometer  90 . 
   This potentiometer  90  comprises a slider terminal  92  connected to the intermediate terminal  26  of the inverter via the control line  62  and the first switch  70 . When the availability of the electrical source is sufficient to allow a normal operation of the motor, the control line  62 , instead of being connected to the end terminal  32  of the assembly of resistors  28 , is connected to the slider terminal  92 . The potentiometer  90  is connected to a manual control  94  provided on the dashboard of the motor vehicle. 
   The manual control comprises a handle  96  of the slider type able to be displaced either in translation or in rotation between two end positions corresponding to a maximum value and a minimum value of the resistance of the potentiometer. When the value of the resistance of the potentiometer is minimal, the slider terminal  92  is merged with the connection terminal  32  and the speed of rotation of the motor is maximal. On the contrary, when the resistance of the potentiometer is maximal, the slider terminal is merged with the intermediate terminal  50  and the speed of rotation of the motor is limited. 
   However, in this case, the origin of the limitation of the speed of rotation of the motor is the operator&#39;s desire, and not the necessity of protecting the electrical source since the control unit has determined that the availability of the latter was sufficient (higher than the upper threshold) to allow the normal operation of the electrical component  4 . 
   This example embodiment, in which an operator can adjust the speed of rotation of the motor according to his wishes, when the availability of the source is sufficient, applies for example to the adjustment of an air-conditioning system in which the adjustment handle  96  can be displaced between a so-called “coolest” position and a “warmest” position in order to adapt the temperature inside the passenger compartment as a function of the outside temperature.