FR2694524A1 - Propulsion system for vehicle - Google Patents

Abstract

The propulsion system has an asynchronous electric motor (2) mechanically coupled to a wheel (3) of the vehicle. An accumulator (4) supplies the motor through a converter circuit (5). The converter circuit can control the flow of power to the motor.An internal combustion engine (7) drives a generator (8) that can supply the drive motor or recharge the accumulator. The accumulator recharging circuit has a second converter (9) to regulate the power delivered to the accumulator from the alternator. A control circuit produces regulating control signals according to electric power flow.

Description

PROPULSION SYSTEM FOR A VEHICLE
The subject of the present invention is a propulsion system for a vehicle having at least one drive wheel and means for producing a signal for controlling the speed of rotation of said drive wheel, comprising
- an electric motor mechanically coupled to said drive wheel;
- a rechargeable electric energy accumulator;
- a fuel engine;
- an electric power generator mechanically coupled to said fuel engine;
- electric energy transfer means electrically coupled to said electric motor, to said generator and to said accumulator for passing a first flow of electric energy between said accumulator and said electric motor, a second flow of electric energy between said generator and said electric motor, and a third flow of electric energy between said generator and said accumulator; and
means for producing a first measurement signal representative of the amount of electrical energy contained in said accumulator
Patent US-A-4,306,156, for example, describes such a system, in which the driving wheels of the vehicle are connected to an alternating electric traction motor by means of a device for adjusting the speed of the vehicle comprising a hydraulic torque converter and an automatic gearbox controlled, in particular, by the vehicle's accelerator pedal.

 The alternating supply voltage of the electric traction motor is supplied by a converter circuit which receives a direct voltage from a rechargeable accumulator as long as the quantity of energy available in the latter is above a determined threshold.

 When this quantity of energy available in the accumulator becomes below this threshold, a control circuit comprising in particular a computer causes the ignition of an internal combustion engine mechanically coupled to a DC generator and the connection of this generator to the converter and the accumulator. This internal combustion engine then supplies, via the generator, the energy required to pull the vehicle and to recharge the accumulator.

 When the quantity of electrical energy available in the accumulator again exceeds the predetermined threshold, the control circuit causes the internal combustion engine to stop and the generator to be disconnected.

The energy necessary for the traction of the vehicle is then again supplied by the accumulator.

 In this system, the voltage and current supplied by the generator when the internal combustion engine is running are substantially constant. A first part of this current is used to power the traction motor, via the converter circuit, and the second part of this current is used to recharge the accumulator. If the traction motor consumes little or no energy, for example when the vehicle is traveling on a downhill slope or when it is stopped, this second part of the current supplied by the generator can be quite high. However, it is known that an accumulator must not be charged by a current greater than a determined value, otherwise it will be damaged. The system described above therefore includes a resistor connected in series between the generator and the accumulator and which is intended to limit the charging current of the latter.

 This resistance dissipates significant energy, which significantly reduces the efficiency of the system. In addition, this resistance must have large dimensions and its temperature can reach high values, which complicates its mounting in the vehicle. In addition, despite the presence of this resistor, the charging conditions of the accumulator are not favorable because of the large variations in the current used for this charge, which can lead to a reduction in the life of this accumulator.

 An object of the present invention is to provide a propulsion system for a vehicle of the same kind as that described by patent US-A-4 306 156 but which does not have the drawbacks, described above, of this last, that is to say a system whose performance is clearly better than that of this known system, which does not include any bulky component and which can have a very high temperature such as the limiting resistance mentioned above, and in which the battery charging conditions can be close to the optimal conditions.

This object is achieved by the claimed system, which is a propulsion system for a vehicle having at least one drive wheel and means for producing a signal for controlling the speed of rotation of said drive wheel and which comprises
- an electric motor mechanically coupled to said drive wheel;
- a rechargeable electric energy accumulator;
- a fuel engine;
- an electric power generator mechanically coupled to said fuel engine;
- electric energy transfer means electrically coupled to said electric motor, to said generator and to said accumulator for passing a first flow of electric energy between said accumulator and said electric motor, a second flow of electric energy between said generator and said electric motor, and a third flow of electric energy between said generator and said accumulator; and
- Means for producing a first measurement signal representative of the amount of electrical energy contained in said accumulator;
this system being characterized by the fact that said means for transferring electrical energy comprise
- first adjustment means for adjusting the intensity of said first and said second flow of electrical energy in response to a first adjustment signal; and
- second adjustment means for adjusting the intensity of said second and said third flow of electrical energy in response to a second adjustment signal;
and by the fact that said system further comprises
- Means for producing a second measurement signal representative of the electrical power transmitted by said first and said second flow of electrical energy;
- Means for producing a third measurement signal representative of the electrical power transmitted by said second and said third flow of electrical energy; and
a control circuit arranged so as to produce said first adjustment signal as a function of said control signal and to produce said second adjustment signal as a function of the difference between said third and said second measurement signal.

 Other objects and advantages of the present invention will be made evident by the description which will be given below with the aid of the appended drawing in which FIG. 1, unique, is a block diagram representing two embodiments of the propulsion system according to the present invention which will only be described by way of nonlimiting examples.

 The propulsion system of a vehicle shown diagrammatically in FIG. 1, in which it is designated by the reference 1, comprises an asynchronous motor 2 whose rotor, not shown separately, is mechanically connected to a driving wheel of the vehicle, also shown in this figure 1 with the reference 3. In this figure 1, the motor 2 and the wheel 3 are separated, their mechanical connection being symbolized by a double line. But it is obvious that this motor 2 and this wheel 3 can be attached to one another, or that they can be connected by means of a transmission shaft and / or a gear train .

 The system 1 also includes a rechargeable electric energy accumulator 4, which is connected to the stator of the motor 2, not shown separately, by means of a converter circuit 5. This converter 5 is arranged so as to supply the energy electric necessary for the operation of the motor 2 in the form of an alternating voltage and current from the electric energy which it receives from the accumulator 4, or other circuits which will be described later, under the form of a DC voltage and current.

 The converter circuit 5 is further arranged so as to regulate the voltage and / or the current which it supplies to the motor 2, as well as, if necessary, the frequency of this voltage and of this current, in response to a signal of adjustment, designated by SR1, which it receives from a control circuit 6 whose functions will be described later.

In other words, the converter 5 is arranged so as to regulate the electric power which it supplies to the motor 2.

 It should be noted here that the electrical connections between the various elements, which have just been described or which will be described below, are symbolized in FIG. 1 by a single line even if these connections consist of several conductive wires, as is well understood the case in particular for the connections between the accumulator 4, the converter 5 and the motor 2. To simplify the understanding of this figure 1, the connections serving for the transfer of electrical energy have been symbolized by thicker lines than those which are used for the transmission of control or measurement signals.

 The system 1 also comprises an internal combustion engine 7 mechanically coupled to the rotor, not shown separately, of an alternating voltage generator 8. In FIG. 1, the engine 7 and the generator 8 are separated, their mechanical connection being symbolized by a double line.

However, it is obvious that this motor 7 and this generator 8 can be joined to one another, or that they can be connected by means of a gear train.

 The stator of the generator 8, not shown separately, is connected to the accumulator 4, and therefore to the converter 5, by means of a second converter circuit 9.

This converter 9 is arranged so as to supply, from the alternating voltage produced by the generator 8, a direct voltage substantially equal to the voltage produced by the accumulator 4. This converter 9 is also arranged so as to adjust, by response to a second adjustment signal designated by SR2, the current and therefore the power which it supplies to the accumulator 4 and to the converter 5. The signal SR2 is produced by the control circuit 6 in a manner which will be described more far.

 The system 1 also includes a monitoring circuit 10, the inputs of which are connected to the accumulator 4 and which is arranged so as to supply the control circuit 6 with a signal designated by SQ, proportional to the quantity of electrical energy available in this accumulator 4. This monitoring circuit 10 will not be described in detail since it can be produced in various ways which are well known to those skilled in the art. It will simply be mentioned that this monitoring circuit 10 generally comprises measurement circuits supplying signals representative of the voltage across the terminals of the accumulator 4, of the charging or discharging current of the latter as well as of its temperature. also the calculation circuits necessary for developing the signal SQ in response to the various measurement signals mentioned above, possibly taking into account the age of the accumulator 4, that is to say the time which s 'has passed since its first entry into service.

 It will be assumed in the present example that the circuit 10 is arranged so that the signal SQ varies between a maximum value when the accumulator 4 is fully charged and a zero value when this accumulator 4 is completely discharged.

The system 1 also comprises a measurement circuit 11 connected to the converter 5 and arranged so as to produce and supply the control circuit 6 with a measurement signal
SP1 proportional to the electric power absorbed by this converter 5 and therefore by the motor 2, as well as a measurement circuit 12 connected to the converter 9 and arranged so as to produce and supply to the control circuit 6 a measurement signal SP2 proportional to the electrical power supplied by the converter 9, and therefore by the generator 8.

 The system 1 may also include a circuit intended to charge the accumulator 4 when the vehicle is stationary near a source of electrical energy such as an outlet connected to a public electrical energy distribution network. Such a charging circuit has not been shown since it has no direct relation to the present invention.

 The control circuit 6 will not be described in detail since the person skilled in the art will have no difficulty in achieving it in one or the other of the many possible ways after having read the explanations of the operation of the system 1 which will to follow.

It will simply be mentioned that, in addition to the signals
SQ, SP1 and SP2 already mentioned, the circuit 6 receives a control signal SA representative of the position of the accelerator pedal of the vehicle. This signal SA can be supplied, for example, by a potentiometer whose cursor is mechanically connected to this accelerator pedal.

This pedal and this potentiometer have not been shown.

 It will also be mentioned that the fuel supply device for the internal combustion engine 7, which comprises for example a carburetor or an injection pump, is arranged so as to regulate this supply in response to an adjustment signal SR3 supplied by the circuit of command 6 under conditions which will be described later.

 It will be assumed that, when this description of the operation of the propulsion system 1 begins, the quantity of electrical energy available in the accumulator 4 is greater than a determined quantity Q1, and that the value of the signal SQ is therefore greater than one SQ1 value corresponding to this quantity of energy Q1.

 The fact that the value of the signal SQ is greater than this value SQ1 has the effect that the control circuit 6 produces the adjustment signal SR3 with a value such that the supply to the internal combustion engine 7 is completely interrupted. This motor 7 is therefore stopped.

 In addition, the control circuit 6 produces the adjustment signal SR2 with a value such that the converter 9 is blocked, that is to say that it does not operate and that its output has a very high impedance.

 When the vehicle equipped with the propulsion system 1 moves under these conditions, the control circuit 6 produces the signal SR1 with a value which depends on that of the signal SA, that is to say on the position of the pedal. accelerator.

 In response to this signal SR1, the converter 5 supplies a certain electrical energy to the motor 2 in the form of an alternating voltage and current, and the power absorbed by this motor 2 in electrical form and that which is restored by this the latter in mechanical form depend on the value of this signal SR1 and therefore on the position of the vehicle's accelerator pedal.

 The electrical energy supplied by the converter 5 to the motor 2 naturally comes from the accumulator 4, which supplies this energy in the form of a DC voltage and current.

 We can therefore consider that a first flow of electrical energy flows, in this case, from the accumulator 4 to the motor 2 through the converter 5, the latter regulating the intensity of this first flow of energy as a function of the value of the adjustment signal SR1 which itself depends on the value of the signal SA and therefore on the position of the vehicle's accelerator pedal. This first flow of electrical energy is symbolized in FIG. 1 by the arrow F1 drawn in dashed lines between the accumulator 4 and the engine 2 and will be designated by the same reference in the following description.

 The amount of electrical energy available in the accumulator 4 obviously decreases as the vehicle equipped with the propulsion system 1 moves.

The signal SQ, which is representative of this quantity of energy therefore also decreases.

When this signal SQ reaches the value SQ1 mentioned above, that is to say when the amount of energy available in the accumulator 4 has only the value
Q1, the control circuit 6 causes the internal combustion engine 7 to start and the converter 9 to start operating.

 The starting of the motor 7 can of course be ensured by a conventional starter powered by an auxiliary accumulator and controlled by an adequate signal supplied by the control circuit 6, but the presence of this auxiliary accumulator and of this starter makes this solution not very advantageous, who was not represented.

 It is therefore preferable to arrange the converter 9 so that it can not only produce a direct voltage from an alternating voltage supplied by the generator 8, as mentioned above, but that it can also operate in the opposite direction, that is to say provide the generator 8 with an alternating voltage from the direct voltage produced by the accumulator 4.

 Such a reversible converter is well known to specialists and will therefore not be described here. It will simply be admitted that, in the present example, the direction of operation of the converter 9 is determined by the polarity of the control signal SR2.

 It can be seen that when the converter 9 is arranged in the manner described above, it is sufficient for the generator 8 to be of any one of the various well-known types of generator capable of also functioning as an engine for the ignition of the internal combustion engine 7 to be insured without the need to use a starter motor and an auxiliary accumulator.

 It is such a solution which has been adopted in system 1 of FIG. 1.

 When the signal SQ reaches the value SQ1, as described above, the control circuit 6 therefore gives the signal SR2 a polarity and a value such that the converter 9 operates in the sense that it supplies an alternating voltage to the generator 8 from the DC voltage produced by the accumulator 4.

 The generator 8 therefore operates as an engine and causes the combustion engine 7 to rotate.

 Simultaneously, the control circuit 6 gives the signal SR3 a value such that the fuel supply device of the engine 7 can operate.

 This motor 7 therefore starts and begins to rotate the generator 8, and the latter begins to produce an alternating voltage.

 The control circuit 6 then changes the polarity of the signal SR2, so that the converter 9 begins to supply a DC voltage in response to the AC voltage which it receives from the generator 8.

 As already mentioned, the direct voltage produced by the converter 9 is substantially equal to the voltage across the terminals of the accumulator 4.

 Furthermore, as will be described in detail below, the electrical energy produced by the converter 9, which comes from that produced by the generator 8, is used, on the one hand, by the converter 5 to supply the motor 2 the energy necessary for its operation and, on the other hand, to recharge the accumulator 4.

 We can therefore consider that, in this case, a second flow of electrical energy flows from the generator 8 to the motor 2 through the converters 9 and 5 and a third flow of electrical energy flows from this generator 8 to the accumulator 4 to through the converter 9.

 These two flows of electrical energy are respectively symbolized in FIG. 1 by the arrows in dashed lines F2 and F3 and will be designated by these same references in the rest of this description.

 It is obvious that in this case the power transmitted to the motor 2 by the energy flow F2 is determined by the value of the signal SR1, exactly as in the case described above where the motor 7 does not operate and where all of the energy required to propel the vehicle is supplied by the accumulator 4.

 I1 is generally recommended to recharge an accumulator with a current at least substantially equal to a constant current determined according to the kind of this accumulator, its maximum capacity and the admissible time to recharge it, this so that its lifespan is' also great as possible.

 To recharge the accumulator 4 with this substantially constant and predetermined current, it is therefore necessary that the power transmitted to this accumulator 4 by the energy flow F3 is also substantially constant and predetermined.

 This latter power is equal to the difference between the power supplied by the converter 9 and that which is absorbed by the converter 5, and it is therefore proportional to the difference between the signal SP2 and the signal SP1, provided of course that the factors proportionality between these signals and the corresponding powers are equal, which is not difficult to achieve.

 The power absorbed by the converter 5 is obviously variable, and it is therefore the same for the value of the signal SP1.

 So that the difference between the signals SP2 and SP1 remains constant, it is therefore necessary to vary the power supplied by the converter 9, to which the signal SP2 is proportional, and therefore to vary the power supplied by the generator 8.

 The latter depends directly on the speed of rotation of this generator 8, and therefore that of the internal combustion engine 7 which, in turn, depends on the mechanical power that this engine 7 must provide and on the value of the signal SR3 which controls its fuel supply device.

So that the power supplied to the accumulator 4 is substantially constant, the control circuit 6 can therefore be arranged so that it regulates the power supplied by the generator 8 by adjusting the speed of rotation of the motor 7 using the signal SR3, the value of this signal
SR3 being determined as a function of the difference between the signals SP2 and SP1.

 So that the power supplied to the accumulator 4 is appreciably constant, the control circuit 6 can also be arranged so that it regulates the mechanical power that the motor 7 must supply.

 For a reason which will be made clear later on in this description, the system 1 must in this case include, in addition to the elements described above, a device producing a signal proportional to the speed of rotation of the motor 7 and / or of the generator 8.

 The voltage produced by the generator 8 being proportional to its speed of rotation, such a device can simply be constituted by a circuit for measuring this voltage, the input of which is connected to the generator 8 and the output of which produces a signal proportional to this voltage. and therefore at the speed of rotation of the generator 8. This circuit has been represented in FIG. 1 with the reference 13 and the signal which it produces will be called signal SV.

 Still in this case, the control circuit 6 is arranged so as to continuously calculate, from the value of the signal SP1 and taking into account the characteristics of the motor 7 and of the generator 8, a set value for the signal SV, this setpoint being equal to that of this signal SV when the speed of rotation of the generator 8 is such that the power it supplies is precisely equal to the sum of the power absorbed by the converter 5 and that which must be used to recharge the battery 4.

 When the vehicle equipped with the system 1 is traveling at constant speed on perfectly horizontal ground, the power consumed by the engine 2 and therefore that which is absorbed by the converter 5 are constant, as is therefore the value of the signal SP1.

 Let us assume that the motor 7, and therefore the generator 8, then rotate at a speed such that the power produced by the latter is exactly equal to the sum of this power absorbed by the converter 5 and that which it is desired to supply to the 'accumulator 4 to recharge it. The signal SV therefore has exactly the set value calculated by the control circuit 6, and the system is in a stable state.

 If now the power absorbed by the converter 5 increases, for example because the driver of the vehicle wishes to accelerate it, the signal SP1 also increases.

 The control circuit 6 then calculates, from this new value of the signal SP1, a new setpoint value for the signal SV, higher than the previous setpoint value. The difference between this new setpoint value and the value of the signal SV therefore becomes positive since, at least at the first instant, the speed of rotation of the generator 8 does not change.

 In response to this difference between the new setpoint value and that of the signal SV, the control circuit 6 gives the signal SR2 a new value such that the power supplied by the converter 9 and therefore that which the generator 8 must produce, decreases.

 The power supplied by the converter 9 having decreased while that which is absorbed by the converter 5 has increased, the difference between these two powers decreases or even becomes negative.

 In the first case, the charge of the accumulator 4 is not interrupted but simply slowed down. In the second case, this charge is interrupted, and the accumulator 4 supplies the converter 5 with the share of the power which is absorbed by the latter and which the converter 9 no longer supplies to it.

 The reduction in the power produced by the generator 8 has the effect that the resistive torque opposed by the latter to the motor 7 also decreases. As a result, the speed of rotation of this motor 7 increases, likewise of course that of the generator 8.

 The signal SV therefore also increases and, when it becomes greater than the new setpoint value mentioned above, the control circuit 6 again modifies the signal SR2 and gives it a value such that the converter 9 again supplies all the power absorbed by the converter 5 and the power required to charge the accumulator 4.

 The power which the generator 8 must supply therefore increases, as does the resistive torque which it opposes to the motor 7. The speed of rotation of this motor 7, and therefore of the generator 8, decreases again, as does of course the signal value SV. But as soon as this value of the signal SV becomes lower than its new setpoint value, the control circuit 6 modifies the value of the signal SR2 so that the power supplied by the converter 9 decreases, which results in the speed of rotation of generator 8 increases again, and so on.

 Similarly, the set value for the signal SV calculated by the control circuit 6 decreases when the power absorbed by the converter 9 decreases. The difference between this new setpoint value and the signal SV therefore becomes negative, and in response to this negative difference, the control circuit 6 gives the signal SR2 a value such that the power supplied by the converter 9 increases.

 This increase has the consequence, on the one hand, that the power supplied to the accumulator 4 increases and, on the other hand, that the rotation speed of the generator 8 decreases until the signal SV becomes lower than its new setpoint.

 The control circuit 6 then again modifies the signal SR2, so that the power supplied by the converter 9 decreases and becomes again equal to the sum of the power absorbed by the converter 5 and that which is necessary for the load of the accumulator 4.

 The speed of rotation of the generator 8 then increases again, and so on.

 It can be seen that as long as the power absorbed by the converter 5 is constant, the speed of rotation of the generator 8 oscillates around an average value which is that for which the signal SV is equal to the set value calculated by the control circuit 6, that is to say for which the power supplied by the converter 9 is equal to the sum of the power absorbed by the converter 5 and that which is necessary to recharge the accumulator 4. The amplitude and the frequency of these oscillations in the speed of rotation of the generator 8 can be kept at low values by a judicious choice of the characteristics of the various elements concerned. In addition, when the power absorbed by the converter 5 varies, the speed of rotation of the generator 8 is adjusted accordingly and, for the time necessary for this adjustment, the accumulator 4 supplies, if necessary, the power that the converter 5 absorbs and that the generator 8 no longer supplies or absorbs that which this generator 8 provides and that the converter 5 no longer absorbs.

 It can be seen that when the control circuit 6 is arranged so as to implement the method which has just been described, the speed of rotation of the generator 8 is adjusted to the desired value without it being necessary to modify the value of the signal SR3 which controls the fuel supply device of the engine 7.

 This signal SR3 can therefore have a constant value chosen so that this engine 7 operates under the most favorable conditions, that is to say that it consumes the least possible amount of fuel and / or that it produces as little as possible of polluting gases.

 Thus, for example, in the case where the fuel supply device for the engine 7 comprises a carburetor having an adjustment butterfly whose position is controlled by the signal SR3, it is possible, and even preferable, to give this signal SR3 a constant value such that this throttle is permanently completely open.

 When the system 1 operates as has just been described, the amount of electrical energy available in the accumulator 4 increases and, after a certain time, reaches a predetermined value Q2, the signal SQ then taking a value SQ2.

 In response to this value SQ2 of this signal SQ, the control circuit 6 causes the engine 7 to stop by giving, for example, the signal SR3 a value such that the fuel supply to this engine 7 is completely interrupted. Simultaneously, the control circuit 6 causes the blocking of the converter 9 by giving the signal SR2 a value such that this converter 9 no longer works and that its output has a very high impedance.

 From this moment, all the energy necessary for the propulsion of the vehicle is again supplied by the accumulator 4. The quantity of electric energy available in the latter then decreases, until it reaches the value Q1. The control circuit 6 then again causes the engine 7 to start and the converter 9 to be released, and the system 1 resumes operation as described above.

 As is clear from the foregoing description, the intensities of the various flows of electrical energy which have been defined above and which circulate between the elements of the system 1 producing or absorbing such energy, i.e. accumulator 4, motor 2 and generator 8, are regulated by converters 5 and 9 which therefore together constitute means for transferring this energy between these elements.

The convector 5 adjusts the intensity of the first and second of these flows as a function of the signal SR1 which itself depends on the signal SA and therefore on the position of the accelerator pedal of the vehicle. This converter 5 therefore constitutes a means of adjusting the speed of the vehicle. The converter 9 adjusts the intensity of the sum of the second and third of these flows as a function of the signal SR2 and therefore constitutes a means of adjusting the load of the accumulator 4.

 Furthermore, the fact that the propulsion system of a vehicle according to the present invention comprises a converter such as the converter 9 which is capable of regulating the amount of energy supplied by generator driven by the internal combustion engine (the generator 8 and the motor 7 in the example of FIG. 1) gives this system numerous advantages over known systems such as that described in the patent US-A-4,306,156 mentioned above.

 Among these advantages, mention will be made of the fact that, whatever the method chosen, the accumulator that the system comprises (accumulator 4 in the example described) can be recharged in good conditions, which increases its lifespan. , and without it being necessary to provide a resistor for limiting the current used for this recharging, which notably increases the efficiency of the system and therefore increases the range of the vehicle, that is to say the distance it can travel before it is necessary to fill its fuel tank.

 In beam, the operating conditions of the internal combustion engine (the engine 7 in the example described) can be optimally chosen, which further increases the efficiency of the system and decreases the amount of polluting gases released by this engine. In addition, the generator coupled to the internal combustion engine may be of the type which produce an alternating voltage, which are less bulky, lighter and less expensive, with equal performance, than those which produce a direct voltage. In addition, the connection between the internal combustion engine and the generator can be arranged so that the latter rotates at high speed, which makes it possible to reduce its dimensions and therefore its price.

 It is obvious that the values Q1 and Q2 between which the amount of electrical energy available in the accumulator 4 varies can be chosen very freely, depending in particular on the type of the accumulator 4.

 Thus, in cases where the accumulator 4 is a lead-acid accumulator, one will preferably choose for Ql a value situated between approximately 20% and 30% of the maximum amount of electrical energy that the accumulator 4 can contain, in order to d Avoid the damage that such an accumulator can suffer when it is discharged until the amount of electrical energy still available is less than this value.

 Still for example, we can choose for Q2 a value close to the maximum amount of electrical energy that the accumulator can contain 4. But we know that the charge efficiency of an accumulator decreases when the amount of energy contained in that -this approaches this maximum amount. it is therefore preferable to choose for Q2 a value lower than this maximum quantity, for example a value of the order of 70% to 80% of the latter, for which the charge efficiency is still quite large. Such a choice further increases the range of the vehicle.

 This autonomy of the vehicle can be further increased by arranging the system 1 so that when its driver releases the accelerator pedal completely, at least part of the kinetic energy of the vehicle is converted into electrical energy, and that part of the less of the latter is used to recharge the battery 4.

 A system 1 arranged in this way will not be described in detail since its production does not pose any particular problem for those skilled in the art.

 It will simply be mentioned that, in such a system, the engine 2 must obviously be of one of the well known dive types of engines capable of operating as generators. Furthermore, the converter 5 must also be capable of operating in the opposite direction to that which has been described above, that is to say that it must be capable of producing a DC voltage and current from the alternating voltage and current supplied by the motor 2 when the latter is operating as a generator.

 In addition, the control circuit 6 must be arranged so as to give the signal SR1 a value and / or a polarity such that the converter 5 operates in the second way mentioned above when the signal SA takes the value which indicates that the driver of the vehicle fully released the accelerator pedal.

 However, the control circuit 6 must also be arranged so that, in this case, the quantity of electrical energy contained in the accumulator 4 does not exceed its maximum admissible value, and that the electrical power supplied by the converter 5 to this accumulator 4 is never greater than that which the latter can absorb without damage.

 To fulfill these conditions, the control circuit 6 can be arranged in various ways.

 Thus, for example, the control circuit 6 can be arranged so as to give the signal SR1 a value such that the electric power supplied by the converter 5, which is indicated by the signal SP1, is at most equal to that which the accumulator 4 can absorb in the case where the signal SQ indicates that this accumulator 4 is not fully charged, and a value such that the converter 5 is blocked otherwise.

Still for example, the control circuit 6 can also be arranged so that the signal SR1 always has the value for which the converter 5 transmits all the electric power supplied by the motor 2 when the latter operates as a generator, whatever this power. This control circuit 6 is then further arranged so that, if the signal SP1 and / or the signal SQ indicate that this power is greater than that which the accumulator 4 can absorb, it gives the signal SR2 the polarity for which the converter 9 operates in the sense that it supplies electrical power to generator 8, and to signal SR3 the value for which the fuel supply to engine 7 is interrupted. This engine 7 is then driven in rotation by generator 8, which operates in wetness, and dissipates in the form of heat the electrical power absorbed by the converter 9. The control circuit 6 is of course arranged in this case so that the value of the signal SR2 is such that this electrical power absorbed by the converter 9 is equal to the difference between that which is provided by the converter 5, which is indicated by the value of the signal
SP1, and that which the accumulator can absorb 4.

 This conversion of at least part of the kinetic energy of the vehicle into electrical energy having the effect of braking the latter, such a system 1 also has the advantage of reducing the wear of the conventional braking device of the vehicle, a device which must in any case to be planned if only for obvious security reasons.

In another embodiment of the propulsion system according to the present invention, which is also shown in FIG. 1, the control circuit 6 is arranged so that the value of Q1 and / or the value of
Q2 are different depending on the value of a mode selection signal SM supplied by a two-position switch arranged on the dashboard of the vehicle. The connection between this switch, which has not been shown, and the control circuit 6 is symbolized in FIG. 1 by the dashed line also designated by the reference SM.

 Thus, when the signal SM has a first value, which corresponds to the first position of the switch, the values of Q1 and Q2 can be quite far from each other, for example being respectively equal to 20% and 80% the maximum amount of energy that can be stored in the battery 4.

 In this first operating mode, the vehicle can therefore travel a fairly long distance without the internal combustion engine being started, which makes it possible for example to cross an agglomeration without emitting polluting gases.

 Likewise, when the signal SM has a second value, that is to say when the switch is in its second position, the values of Q1 and Q2 can be fairly close to one another, for example being respectively equal to 40% and 60% of the maximum amount of energy that the accumulator can contain 4.

 In this second operating mode, the internal combustion engine is started at shorter intervals than in the first operating mode, but the efficiency of the system is improved by the fact that the charging efficiency of the accumulator is higher, and the service life of the latter is extended. This second operating mode is advantageously used when the vehicle is driving in the middle of the countryside.

 In a variant of this second embodiment of the system according to the invention, the switch supplying the signal SM can take one or more other positions in addition to those which have been mentioned above, this signal SM then having a different value for each position of this switch. In addition, the control circuit 6 is arranged so that the value of Q1 and / or the value of Q2 are different for each of the values of the signal SM.

 Thus, for example, the values of Q1 and of Q2 can be those which were mentioned above for two of the values of the signal SM and, for a third value of this signal SM, to be respectively equal to 70% and 90% of the maximum amount of energy that the accumulator can contain 4.

 This third operating mode can be advantageously used when the vehicle is driving in the middle of the countryside and its driver knows that he will then have to cross a built-up area. Indeed, when the vehicle arrives at the entrance to the agglomeration, the amount of energy available in the accumulator 4 will be at least equal to 70% of the maximum amount of energy that it can contain. This amount of available energy will therefore probably be sufficient for the vehicle to be able to cross this agglomeration by operating according to the first mode described above, without the internal combustion engine being started.

 It is obvious that other modifications and / or additions can be made to the propulsion system of a vehicle described above without departing from the scope of the present invention.

 Thus1 in particular, the internal combustion engine 7 of the system 1 of FIG. 1 can be replaced by any other type of fuel engine, that is to say by any other engine using the combustion of a fuel for producing mechanical energy such as, for example, a gas turbine.

 Likewise, it is obvious that the system according to the present invention can be used in a vehicle comprising several driving wheels. In such a case, each pair of driving wheels, or even all of these, can be driven by a single motor such as the motor 2 of FIG. 1, by means of well known mechanical transmission means, or each driving wheel can be driven by a particular motor.

Claims (3)

 1. Propulsion system (1) for a vehicle having at least one drive wheel (3) and means for producing a control signal (SA) of the speed of rotation of said drive wheel (3), comprising  - an electric motor (2) mechanically coupled to said drive wheel (3);  - a rechargeable electric energy accumulator (4);  - a fuel engine (7);  - an electric power generator (8) mechanically coupled to said fuel engine (7);  - electrical energy transfer means (5, 9) electrically coupled to said electric motor (2), to said generator (8) and to said accumulator (4) for passing a first flow of electric energy (F1) between said accumulator (4) and said electric motor (2), a second flow of electrical energy (F2) between said generator (8) and said electric motor (2), and a third flow of electrical energy (F3) between said generator ( 8) and said accumulator (4); and  - means (10) for producing a first measurement signal (SQ) representative of the amount of electrical energy contained in said accumulator (4);  characterized by the fact that said electrical energy transfer means (5, 9) comprise  - first adjustment means (5) for adjusting the intensity of said first (F1) and said second flow of electrical energy (F2) in response to a first adjustment signal (SR1); and  - second adjustment means (9) for adjusting the intensity of said second (F2) and said third flow of electrical energy (F3) in response to a second adjustment signal (SR2);  and by the fact that said system (1) further comprises  - means (11) for producing a second measurement signal (SP1) representative of the electrical power transmitted by said first (F1) and said second flow of electrical energy (F2);  - means (12) for producing a third measurement signal (SP2) representative of the electrical power transmitted by said second (F2) and said third flow of electrical energy (F3); and  - a control circuit (6) arranged so as to produce said first adjustment signal (SR1) as a function of said control signal (SA) and to produce said second adjustment signal (SR2) as a function of the difference between said third ( SP2) and said second measurement signal (SP1).  2. Propulsion system according to claim 1, characterized in that said control circuit (6) is arranged so as to produce said second adjustment signal (SR2) with a value such that said difference between said third (SP2) and said second measurement signal (SP1) is at least substantially equal to a determined value.  3. propulsion system according to claim 2, characterized in that it comprises means (13) for producing a fourth measurement signal (SV) representative of the speed of rotation of said generator (8), and in that said control circuit (6) is arranged so  - calculating a set value for said fourth measurement signal (SV) as a function of said second measurement signal (SP1);  - firstly giving said second adjustment signal (SR2) a value such that said intensity of the second (F2) and of the third flow of electrical energy (F3) decreases or increases depending on whether said difference between said third (SP2) and said second measurement signal decreases or, respectively increases; and  - when said fourth measurement signal (SV) reaches said set value, to give said second adjustment signal (SR2) a value such that said difference between said third (SP2) and said second measurement signal (SP2) is again equal to said determined value.