FR2533375A1 - Electrical energy generating device for a vehicle, with multi-phase alternator and voltage regulator. - Google Patents

Abstract

Electrical energy generating device for a vehicle, with multi-phase alternator and voltage regulator, characterised in that the alternator 1 has a coiled central stator with phase windings and a peripheral rotor with permament excitational magnets, the said phase windings being connected to a bridge rectifier 2, whose output is connected to a capacitor 3 configured in parallel relative to the regulator, which comprises a chopper circuit 4 whose input is slaved to the output state of a two-input comparator responding to the instantaneous voltage across the terminals of the battery and to a predetermined reference voltage, the output of the chopper being connected to an inductor 5 linked to a charging terminal of the battery and comprising, configured in parallel on either side of itself, a battery side overvoltage limiting Zener diode 7 and a passing diode 8 for utilising the current induced on cutting off the chopper to charge the battery.

Description

Electric power generation device for vehicle, with polyphase alternator and voltage regulator.

The electricity generation system most commonly used in automobiles today generally includes
- a three-phase alternator mounted in a triangle, at overdrive speed compared to the automobile engine via a pulley and belt transmission.

 - An excitation of the alternator by rotating winding, the excitation energy being supplied via coals and rings.

 - Cooling of the parentilator alternator rotating in synchronism.

 - An electronic or electro-mechanical voltage regulation system by opening and closing the excitation circuit, thus ensuring a rectified armature voltage equal to the voltage across the battery and consumers.

This system has drawbacks in the following areas: integration into the engine block, maintenance, efficiency, load characteristics. Integration into the alternator's engine block is interesting in order to minimize the volumes and masses contained in the engine compartment. However, this system does not lend itself to it
- by the need for a transmission with overdrive ratio (of order 2);
- by the need for air and non-fluid cooling due to the presence of sliding electrical contacts;
- by rotor dimensions which do not make it possible to envisage it even as a partial replacement of the flywheel.

 On the other hand, this system requires maintenance and replacement at a fixed date of the sliding contacts, as well as maintenance relating to the transmission belt.

I1 also presents a mediocre yield of the order of 30 to 50% due to
- the high internal impedance of the alternator, i.e. a high resistance causing high losses by effect
Joule, and a high inductance, resulting in a strong induction in the machine leading to high magnetic losses.

- The low armature voltage (equal to the battery voltage) imposes for a given useful power, a large armature current generating high magnetic losses and by effect
Joule.

 - The presence of ventilation, made compulsory due to the high losses in the alternator, resulting in losses proportional to the cube of the speed.

 - The need for an excitation current, hence a power dissipated by this circuit.

 - The need to rotate at a high speed to obtain the necessary voltage for the load which is a source of mechanical (transmission) and magnetic (high frequency) losses.

 - The presence of rectifier diodes in a low voltage circuit.

 - Finally, due to its high internal impedance, the alternator has a poor charging characteristic at low speed.

This is how in town, during traffic jams in winter and at night, we can witness operating incidents affecting the engine of the stalling car, because the battery has been discharged in consumers due to the insufficient flow from the alternator.

The present invention relates to a device for generating electrical energy for a vehicle which is the subject of a new overall arrangement of a polyphase alternator and voltage regulator, aiming to eliminate the aforementioned drawbacks, and more particularly:
- maximize the efficiency of the generation and regulation of electrical energy on the motor vehicle and facilitate its integration into the engine block;
- minimize the cost of increasing the performance obtained;
- to remove maintenance on a fixed date;
- to supply the power necessary for the battery and consumers at all operating points.

 Essentially for this purpose, the device for generating electrical energy for a vehicle according to the invention, with polyphase alternator and voltage regulator, is characterized in that the alternator is with a wound central stator with phase windings and a peripheral rotor with magnets permanent excitation, said phase windings being connected to a bridge rectifier, the output of which is connected to a capacitor in shunt with respect to the regulator, which comprises a chopper circuit whose input is slaved to the output state d '' a comparator with two inputs responding to the instantaneous battery voltage and to a predetermined reference voltage, the output of this chopper being connected to an inductor connected to the battery charging terminal and comprising bypass on both sides from it a Zener diode for overvoltage limitation on the battery side, and a pass-through diode allowing the current induced at the cut of the chopper to be used for battery charging.

Other particularities and aspects of the invention will appear in addition in the following description of an embodiment of an electrical energy generating device thus designed, shown by way of example in the appended drawing, in which
fig. 1 is a block diagram of the entire device according to the invention;
fig. 2 is an axial sectional view of the alternator;
fig. 3 is a sectional view of the following alternator
III-III of fig. 2;
fig. 4 is an electrical diagram of the entire device detailing an example of a regulator circuit;
fig. 5 is an axial section view of an embodiment of an inductor used in the device according to the invention.

As can be seen in the block diagram in FIG. 1, the device comprises a polyphase alternator 1 which is here, by way of nonlimiting example, of the three-phase type and whose phase windings are connected to a bridge rectifier 2 comprising six diodes arranged so as to effect in a known manner the AC voltage conversion DC voltage. In the example illustrated, the bridge rectifier is three-phase. The outputs of this rectifier bridge are connected to a capacitor 3 placed in derivation with respect to a chopper circuit 4, the output of which is connected to an inductor 5 connected to the charging terminal of the battery 6 and comprising in derivation, on the one hand and on the other hand, a diode
Zener 7 for overvoltage limitation on the battery side and a passing diode 8 for the current induced when the chopper is cut off, so as to also use it for battery charging. The chopper 4 is subjected to a control device 9, responding to- the instantaneous battery voltage and at a predetermined reference voltage, in order to operate the chopper as will be seen below.

The alternator 1 is a three-phase alternator with a wound stator mounted in a star shape by way of example. The stator is formed of a ferromagnetic core 10 composed of sheets mounted on a central axis of non-magnetic steel 11, this core being provided with notches 12 receiving the phase conductors in the usual manner not shown here. The rotor consists of a ferromagnetic hoop 13 on which are bonded ferrite sectors 14 forming pole pieces alternately north-south. This rotor is here represented as being octopolar, with eight ferrite sectors extending over 360 each, separated by non-magnetic shims 15. Some of these shims are crossed by studs 16 of non-magnetic steel, here 4 arranged at 900, and serving as assembly elements with two lateral flanges 17 and 18 of the rotor, which rest by means of bearings 19 on the axis 11. A flange 20, fixed on the axis 11, for example by screwing, serves mounting bracket for the alternator. We can already note that the advantages of such an alternator are as follows:
Very low internal impedance, due to the very low resistance of the internal stator and the generous dimensioning of the notches, as well as a very low inductance, because the magnetic fluxes pass through magnets of high thickness (in particular greater than 10 mm);
- possibility of turning at the same speed as the engine;
- no need for cooling, since it is only subject to low electrical and magnetic losses;
- outer rotor of suitable diameter to lend itself to partial replacement of the flywheel;
- possibility of debiting the maximum load at low speed thanks to the very low internal impedances;
- absence of electric excitation circuit,
- absence of sliding contacts.

 All these points contribute to making this alternator a high efficiency generator, easily integrated into the engine compartment and requiring practically no periodic maintenance.

The chopper 4 and its control circuit 9 are detailed in FIG. 4. The chopper itself is made up, for example, of two transistors 21 and 22 forming a PNP-NPN composite assembly. Transistor 21 is a bipolar DARLINGTON PNP and transistor 22 is a bipolar DARLINGTON NPN. This choice of composite mounting of the transistors 21 and 22 is interesting in that it makes it possible to take advantage of the specific advantages of the transistors of the PNP and NPN type. In particular, the use as transistor 21 of a PNP transistor has the following advantages
the transistor is easily bootable since it suffices to apply a negative emitter base voltage thereto and since the emitter voltage here is the highest voltage available at any time on the vehicle, the base voltage can only be lower therein or equal;
- This transistor 21 can be of low power installed compared to the transistor 22 which it controls and therefore it is in a range of power readily available on the market at low prices.

 The NPN transistor 22 also has the advantage of being widespread on the market at a low cost in its power range.

 The base of transistor 21 is controlled by a transistor 23 which, in the on state, imposes a current sufficient to saturate the transistor 21. This transistor 23 is controlled by the intermediary of a transistor 24 driving its basic bias circuit, and whose own base is subjected to the output voltage of a comparator 25. This comparator 25 is a differential amplifier whose non-inverting input is connected by a resistor 26 to the cursor of a potentiometer 27 interposed between a conductor 28, connected to the positive pole of the battery by means of a switch 29 corresponding here to the ignition key of the vehicle, and ground. The inverting input of comparator 25 is connected to the cursor of a potentiometer 30 interposed between ground and a regulator 31 supplied by the conductor 28 and supplying the potentiometer with a reference voltage Vr. These potentiometric sockets are such that the battery voltage Vb taken at 27 is compared to an optimal reference voltage Vr for charging lead-acid batteries, which is here chosen to correspond to 14.45 volts for a so-called 12 volt battery, being at see that the regulator 31 develops here a voltage Vr of 5 volts intended to supply the electronic circuit, the comparison of reference voltage-battery voltage being corrected by potentiometers 27-30 to be representative of the aforementioned 14.45 volts. switch 29 is open, the chopper circuit 4 is also open, that is to say non-conductive, the corresponding control 9 being in fact not supplied. When the switch 29 is closed and the motor is running, if the voltage applied to the non-inverting input of comparator 25 is less than the reference voltage applied to its inverting input, the output of this comparator switches to low state, which polarizes transistor 24, which in turn polarizes transistor 23, which turns transistors 21 and 22 of the chopper on. Under these conditions, the armature voltage of the alternator 1 rectified by the rectifier 2 is applied to the inductor 5 and to the battery. As a result, the voltage at the non-inverting input of the comparator 25 rapidly becomes higher than the reference voltage applied to its inverting input and the output of the comparator goes high plus 5 volts. As a result, transistor 24 ceases to be biased on conduction and with it transistor 23, which has the effect of blocking the transistors 21 and 22 of the chopper which is open. A reaction resistor 32 connects the output of the comparator to its non-inverting input and the effect of this resistor with the resistor 26 is to introduce hysteresis in the operation of the comparator, so that the latter responds by tilting for a voltage deviation V more or less from the reference voltage applied to its inverting input. The chopper 4 and its control 9 therefore carry out a transformation from high DC voltage to low DC voltage, thanks to cutting by the chopper. the voltage from the alternator, cutting controlled by the control 9 as we have just seen.

There are thus available for the usual ranges of speeds of a voltage to the output of rectifier 2 sufficiently high to ensure that whatever the load (battery 6 and consumers) a low armature current with magnetic loss and by effect
Joule weak. Capacitor 3 has a double rail
- it protects the power transistors of the chopper 4 against significant voltage variations (dV / dt)
- It absorbs reactive energy from the phase windings of the alternator 9 during the opening sequences of the chopper 4.

 It can be of low capacity of the order of 50 F) thanks to the low inductance of the alternator and it is therefore of a volume and of a cost compatible with use on an automobile.

Inductance 5 has a dual role
- absorb the voltage difference between the battery 6 and the voltage across the capacitor 3 during the closing sequence of the chopper 4;
- Prevent damaging current discontinuities in the battery 6 and consumers, thanks to the closing of the induction current circuit provided by the diode 8 in the opening phases of the chopper, i.e. - say of non-conduction of it.

This inductance can be here
- small footprint and therefore easy integration;
- very low resistance, causing only a small loss by the Joule effect;
- a very low mass of copper at a reduced cost compatible with an automotive application. It will be noted that the Zener diode 7 for protection against overvoltages also ensures the safety of the device in the event of voluntary or non-disconnection of the positive terminal of the battery 6 when current flows in the inductor 5, the voltage peak
r a current in resulting at the terminals of the inductance which can then be written by the Zener diode 7 and by the path of diode 8 by which the circuit of said induction current closes.

 Also shown in FIG. 5 an original structure preferred for the realization of the inductor 5.

This inductance comprises a cylindrical magnetic steel carcass 5a and a cylindrical core 5b forming a plug for the carcass and support for a winding 5c comprising a small number of turns, the core also being of magnetic steel. This core is separated from the bottom of the carcass by a small air gap 5d. This leads in linear magnetic regime to a very low reluctance R. As the self-inductance coefficient is L = n2jR, in which n is the number of turns of the winding, we see that for ante value of L given n will be all the smaller when R is low. The number of turns n being small, the resistance and the mass of the winding are low and the size of the inductance is relatively small. One can choose a self-inductance coefficients L such that the operating frequency of the chopper 4 does not generate audible noise or significant loss by switching.

 Of course, many variants can be made to such an assembly without departing from the scope of the invention.

Claims (5)

 1. Device for generating electrical energy for a vehicle, with polyphase alternator and voltage regulator, characterized in that the alternator (1) has a central wound stator with phase windings and a peripheral rotor with permanent excitation magnets, said phase windings being connected to a bridge rectifier (2), the output of which is connected to a capacitor (3) bypassed with respect to the regulator, which comprises a chopping circuit (4) whose input is slaved to output state of a comparator (25) with two inputs responding to the instantaneous voltage at the terminals of the battery and to a predetermined reference voltage1 the output of the chopper being connected to an inductor (5) connected to a charging terminal of the battery and comprising, on bypass on either side of it, a Zener diode (7) for overvoltage limitation on the battery side and a diode (8) conducting to use the current induced at the cutting of the chopper for charging battery.  2. Device for generating electrical energy according to claim 1, characterized in that the stator (10) of the alternator (1) is composed of notched sheets containing the phase windings and fixed on a central axis (of non-magnetic steel , the rotor consisting of a ferromagnetic hoop (13) in which are bonded ferrite sectors in even number magnetized alternately North-South, separated by non-magnetic shims (15), some of which are pierced with holes receiving organs of assembly (16) in non-magnetic steel holding two lateral flanges (17, 18) for assembling the assembly, which rest on bearings integral with the central axis (11) - mentioned above.  3. Electric power generator device according to one of claims 1 or 2, characterized in that the voltage chopper (4) consists of two DARLINGTON transistors, one bipolar PNP (21) and the other bipolar NPN (22) forming a composite assembly where the base of the NPN transistor is connected to the collector of the PNP transistor, the emitter of the latter being connected to the collector of the NPN transistor and to the plus pole of the aforementioned capacitor Ç3), and the emitter of the transistor NPN being connected to the cathode of the diode (8) and to the inductor (5), the base of the PNP transistor forming the chopper control input.  4. Device for generating electrical energy according to any one of the preceding claims, characterized in that the control (9) of the chopper comprises at least one transistor (23) whose base is biased according to the output state of the comparator ( 25), the latter having a hysteresis fixed by a feedback loop so that its output goes from a high level to a low level for a voltage difference V of the two aforementioned voltages applied to these inputs, the voltage state battery lower than said reference voltage corresponding to a command to close the chopper and the reverse state corresponding to a command to open the chopper.  5. An electrical energy generating device according to any one of the preceding claims, characterized in that the inductance (5) is composed of a carcass of cylindrical ferromagnetic steel receiving a core of ferromagnetic steel forming plug of the carcass and conductive winding support wound between carcass and core, an axial air gap (5d) being provided between carcass and core at the level of the axis of revolution of the inductance.