JP4379712B2 - Vehicle alternator - Google Patents

Description

  The present invention relates to a vehicular AC generator, and more particularly to a vehicular AC generator excellent in load dump surge absorption characteristics.

In a generator of a vehicle charging system, a large overvoltage (hereinafter also referred to as a load dump voltage) is applied to the armature winding when the battery terminal is disconnected due to engine vibration or when a high power load is suddenly cut off. ) May occur. In order to protect circuit elements and the like from this load dump voltage generated by the armature winding, in Patent Document 1, the three diodes of one arm of the full-wave rectifier of the generator are usually called zener diodes. It has been proposed to absorb the load dump voltage by using a constant voltage diode or by providing a constant voltage diode in parallel with the full-wave rectifier. Hereinafter, this method is abbreviated as a Zener type full-wave rectifier. In the following description, Zener diodes should be taken to mean diodes with constant voltage breakdown characteristics, ie constant voltage diodes.
Japanese Patent No. 2751153

However, since the vehicle power supply voltage is being boosted to a high voltage of 42 V, for example, and the output current of the vehicle AC generator is also increasing, the above-described Zener full-wave rectifier increases the vehicle power supply voltage. At the same time, the breakdown voltage of the Zener diode must be increased.To that end, it has been manufactured according to the conventional vehicle power supply voltage, or instead of a general-purpose low-voltage Zener diode, a new Zener diode with a high breakdown voltage is newly added. Necessary. However, there is a problem that such a high-current Zener diode having a high breakdown voltage is relatively difficult to manufacture and has a low yield and a high manufacturing cost compared to a high-current Zener diode having a lower breakdown voltage. is there.
In addition, when a load dump voltage is generated at the time of outputting a large current, heat generation corresponding to the breakdown voltage × current is generated in the Zener diode, and the temperature rise may exceed an allowable value. That is, if the allowable maximum heat generation amount per unit time of the semiconductor chip has a certain limit, when the breakdown voltage increases, the allowable maximum breakdown current decreases proportionally.

  In addition, when the armature current suddenly decreases, the non-negative open-circuit voltage rises. Therefore, the load dump decrease is usually referred to as including the above two phenomena. Therefore, the load dump voltage referred to in this specification is the above two causes. Means an increase in armature voltage. The time constant of the load dump voltage component related to the release of the stored magnetic energy of the former armature winding linkage timing circuit is much smaller than the time constant for eliminating the increase in the no-load voltage.

  The present invention has been made in view of the above problems, and an object to be solved is to provide a vehicle AC generator that can absorb a load dump voltage satisfactorily while suppressing an increase in circuit cost.

  An AC generator for a vehicle according to the present invention made for solving the above-described problems is wound around a field winding for exciting a rotating multipole magnetic pole and an armature core disposed opposite to the multipole magnetic pole. An armature winding, a field current control switching element that is connected in series with the field winding and controls the field current that is passed through the field winding, and each of the armature windings that constitute the armature winding In a vehicle AC generator comprising a full-wave rectifier that rectifies a power generation voltage output from a phase winding and charges an in-vehicle battery to a predetermined charging voltage Vb, an intermediate tap provided in each phase winding and a predetermined And an overvoltage absorption circuit including a plurality of constant voltage diodes having a breakdown voltage smaller than the charging voltage Vb.

  In the following description, the voltage output from all turns of the armature winding when a load dump occurs is referred to as the load dump voltage, and the voltage output from the intermediate tap is referred to as the load dump voltage divided to distinguish. To do.

  That is, in the present invention, when the load dump voltage is generated and the divided voltage of the load dump voltage extracted from the intermediate tap exceeds the breakdown voltage of the constant voltage diode, the constant voltage diode breaks down, and thereby the armature winding and the chain are broken. The magnetic energy accumulated in the intersecting magnetic circuit depends on the zener diode absorption power approximately equivalent to the breakdown voltage x current of the constant voltage diode, the electrical resistance of the armature winding through which the zener diode breakdown current flows, the electrical resistance of the wiring, etc. It is consumed by the consumed power and disappears. Similarly, the component related to the increase in the no-load voltage, which is the other component of the load dump voltage, is also absorbed at a low voltage by the breakdown of the constant voltage diode.

  Therefore, according to the present invention, the load dump voltage generated in the armature winding is applied to the Zener diode of the conventional Zener diode type full-wave rectifier, and the breakdown voltage is small, so that it is easy to manufacture and easily obtain. The load dump problem can be satisfactorily solved by using a constant voltage diode.

  In addition, the forward voltage drop of the constant voltage diode that is forward with respect to the load dump voltage among the plurality of constant voltage diodes connected in a star shape also helps absorb the load dump energy. it can.

  Furthermore, since the divided voltage of the load dump voltage applied to the overvoltage absorption circuit is smaller than the load dump voltage, the power that the constant voltage diode of the overvoltage absorption circuit must absorb when the load dump occurs (the breakdown voltage of the constant voltage diode × The load dump current) can also be reduced compared to the case where the load dump voltage is applied to the constant voltage diode, or the absorbable load dump current can be increased.

  After all, by using an overvoltage absorption circuit consisting of a constant voltage diode connected in a star shape to an armature winding with an intermediate tap, it is possible to reduce the breakdown voltage required for the constant voltage diode and reduce the power loss of the constant voltage diode. The load dump problem can be solved while greatly reducing the burden of the constant voltage diode.

  When the constant voltage diode of the overvoltage absorption circuit breaks down due to the load dump voltage (exactly its voltage division), the ratio between the total number of turns of the phase winding and the number of turns up to the intermediate tap (hereinafter referred to as the turn number ratio) The load dump voltage is applied from the phase winding to the full-wave rectifier according to the above), but the turn dump voltage is less than the breakdown voltage of other circuit elements such as a diode of the full-wave rectifier. The number ratio and the breakdown voltage of the constant voltage diode of the overvoltage absorption circuit may be determined. The intermediate tap can be taken out at any position. However, in order to enhance the effects of the following invention, when the number of turns of the phase winding is n, the number of turns is preferably less than about n / 2. It is. Further, since the extraction of the intermediate tap from the phase winding is for extracting the divided voltage of the phase winding to the overvoltage absorption circuit, the magnetic circuit around which the phase winding is wound, preferably a transformer in the stator core. A secondary coil may be provided so as to be coupled, and a voltage induced in the secondary coil may be guided to the constant voltage diode of the above-described overvoltage absorption circuit. In this case, the output terminal of the secondary circuit corresponds to the intermediate tap in the present invention.

  In a preferred aspect, the breakdown voltage Vz of the constant voltage diode is set to 0.5 Vb ≦ Vz ≦ Vb with respect to the charging voltage Vb of the in-vehicle battery. However, the intermediate tap extraction position should be set so that the load dump voltage generated by the entire armature winding does not destroy other circuit elements. In this way, it is possible to use a general-purpose constant voltage diode having a low breakdown voltage without connecting a plurality of conventionally used constant voltage diodes in series to a high-voltage vehicle AC generator. it can.

  In a preferred aspect, the current density of the constant voltage diode of the overvoltage absorption circuit is set lower than the current density of the diode of the full wave rectifier. In this way, since the heat generation of the constant voltage diode of the overvoltage absorption circuit can be kept low, the allowable surge resistance, which is dominated by the temperature rise accompanying the heat generation, can be increased, and the surge absorption capability can be increased.

  In a preferred aspect, the node is connected to a cathode electrode of each constant voltage diode and supplies power to the field winding. Thereby, since the voltage applied to the generated voltage control device and the field winding can be made lower than the output voltage of the generator, the electric corrosion resistance and the insulation can be improved. In addition, since an increase in field current when a load dump voltage is generated can be suppressed, an increase in no-load voltage due to an increase in the amount of field magnetic flux can be suppressed well.

  In a preferred embodiment, the flywheel diode has a flywheel current attenuation circuit having a flywheel diode and an impedance element connected in series with the flywheel diode and connected in parallel with the field winding. Thereby, although the product of the breakdown voltage and current when absorbing the load dump energy does not change, the time constant of the field circuit can be reduced, so that the breakdown time can be shortened. That is, the temperature rise of the constant voltage diode can be suppressed.

  In a preferred aspect, the impedance element is constituted by a constant voltage diode whose cathode electrode is connected to the cathode electrode of the flywheel diode. As a result, when the flywheel current of the field circuit is flowing, the voltage at the winding terminal is regulated regardless of the magnitude of the current, so that the withstand voltage design of the field circuit is highly reliable, so that low-cost and reliable surge absorption is possible. It becomes possible. The impedance element may be configured by connecting a resistance element and an inductance element in series or in parallel.

  In a preferred aspect, the semiconductor device includes a transistor for shorting an impedance element connected in parallel with the impedance element. As a result, the pulsation rate of the field current due to field adjustment can be reduced usually by reducing the impedance of the flywheel circuit, and the field time constant can be shortened by opening or switching the transistor when necessary. . That is, the surge absorption capability can be enhanced without compromising part of the power generation adjustment function of the generator.

  A preferred embodiment of an automotive alternator according to the present invention will be described below. The present invention is not limited to the following embodiment, and the technical idea of the present invention may be implemented by other known techniques or a combination of equivalent techniques.

  A first embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram of an automotive alternator according to this embodiment.

  This AC generator for a vehicle includes a regulator 9 that is a power generation voltage control device that appropriately controls the charging voltage of a 42V-system vehicle-mounted battery to which a generator output terminal 10 not shown is connected, and a field connected to the power generation control device 9. A magnetic winding 8, a multipole magnetic pole of a rotor (not shown) magnetized by the field winding 8, an armature core (not shown) arranged opposite to the multipole magnetic pole, and three pieces housed in a slot of the armature core Phase armature winding 1, three-phase full-wave rectifier 2 connected to the winding end of three-phase armature winding 1, and 1 / of the total number of turns of the winding from the neutral point in armature winding 1 3 has an intermediate tap 4 drawn out at a position of 3 turns, and an overvoltage absorption circuit 5 connected to the intermediate tap 4.

  The overvoltage absorption circuit 5 includes three constant voltage diodes (hereinafter referred to as “star-connected”) in which each anode electrode is individually connected to an intermediate tap of each phase winding of the armature winding 1 and each cathode electrode is star-connected to the node 7. It is also called a Zener diode. The breakdown voltage Vz2 of the Zener diode 6 is set to 26V, which is set in the range of 0.5Vb (21V) ≦ Vz2 (26V) ≦ Vb (42V) with respect to the actual charging voltage Vb = 42V of the in-vehicle battery. Has been.

  The load dump absorption effect of this embodiment will be described with reference to the characteristic diagrams shown in FIGS. FIG. 2 is a voltage waveform diagram showing an example of a case where a load dump voltage (load dump surge) output from the entire armature winding is clipped by a conventional Zener diode. FIG. 3 is a characteristic diagram showing a relationship between a breakdown voltage (clip voltage) and a breakdown current (clip current) of a Zener diode in a VI characteristic of a conventional generator. FIG. 4 is a voltage waveform diagram showing the clipping effect by the overvoltage absorption circuit of this embodiment. FIG. 5 is a characteristic diagram showing the relationship between the breakdown voltage (clip voltage) and breakdown current (clip current) of the Zener diode in the VI characteristics of the generator in this embodiment.

  According to this vehicle alternator, as shown by the broken line in FIG. 2, it is not the absorption indicated by the solid line indicated by the height V1 with respect to the generation of the surge voltage when the load of high power is suddenly cut off. Since the voltage division of the load dump voltage from the low voltage intermediate tap can be absorbed by the Zener diode 6, the breakdown voltage can be lowered as shown as V2 in FIG.

  As can be seen from the comparison between FIG. 3 and FIG. 5, the current drawn from the intermediate tap 4 when the Zener diode 6 breaks down is approximately the ratio of the electrical resistance to the intermediate tap of the armature winding and the divided voltage of the load dump voltage. Assuming that they are determined, since both of these are determined by the take-out position of the intermediate tap 4, that is, the winding ratio, and both of them can be considered to decrease, the breakdown current flowing through the Zener diode 6 causes the Zener diode to become a three-phase armature. It can be considered that it is substantially equal to the conventional example provided in the whole winding. For this reason, it can be considered that the power loss and heat generation of the Zener diode 6, which is the product of the breakdown voltage and the breakdown current, are reduced by the decrease in the breakdown voltage.

  Since the time constant determined by the inductance and resistance value of the circuit is originally unchanged, the surge energy that is the product of these voltage, current, and time can be reduced. The intermediate tap 4 connected to the overvoltage absorption circuit 5 and the winding end connected to the three-phase full-wave rectifier 2 have a transformation ratio of 3 to 1 in this embodiment due to the winding ratio of the armature winding 1. Therefore, the generator voltage can be suppressed to less than the element breakdown voltage by absorbing small surge energy. For this reason, even in a large power generator of 42V (36V system) or the like, surge energy can be absorbed by a conventional rectifier.

  In this vehicular AC generator, a field current can be supplied to the field winding 8 from another circuit during low rotation.

  Another embodiment will be described with reference to a circuit diagram shown in FIG.

  In this embodiment, a Zener diode 12 and a transistor 13 are added to the flywheel circuit of the field winding 8 in addition to the flywheel diode 11 with respect to the first embodiment. A Zener diode 12 connected in series with the flywheel diode 11 is connected in parallel with the field winding 8. The transistor 13 is connected in parallel with the Zener diode 12. The base electrode of the transistor 13 is connected to a time constant reduction signal terminal 15 that continuously outputs a low voltage when a signal from the overvoltage detection terminal 14 of the regulator 9 is received.

  A high base drive voltage is sent from the time constant reduction signal terminal 15 of the regulator 9 so that the transistor 13 remains ON during normal power generation operation. However, when the generator becomes overvoltage, such as during load dump, the regulator 9 that has received the overvoltage detection signal from the terminal 14 stops high voltage generation of the time constant reduction signal circuit and turns off the transistor 13. At the same time, since a high voltage is generated, the regulator 9 turns off the field current, which causes the field winding to generate a reverse voltage in the flywheel circuit. As a result, the Zener diode 12 breaks down and the flywheel current is reduced. It flows through the Zener diode 12. By newly generating a flywheel loss due to the product of the breakdown voltage and the flywheel current, the magnetic energy of the field circuit is also quickly dissipated, and the time constant can be substantially shortened. That is, in this embodiment, by using the Zener diode 12 instead of the resistor, the maximum reverse voltage applied to the transistor can be limited regardless of the flowing current, so that reliable surge absorption can be achieved without impairing the breakdown voltage reliability of the transistor. The effect is obtained.

(Modification)
In the above embodiment, the midway tap of the armature winding is taken out from the 1/3 point, but it goes without saying that any other division ratio of 1/2 point or 2/3 point can be taken arbitrarily.

  Another embodiment will be described with reference to FIG.

  In this embodiment, the field winding 8 and the flywheel diode 11 are removed from the node of the overvoltage absorption circuit 5 shown in FIG. In this case, the field winding 8 can be supplied with power from the vehicle battery as usual.

  In this way, since any one zener diode 6 breaks down due to an increase in the partial pressure of the load dump voltage applied from the intermediate tap 4 when the load dump occurs, the load dump voltage suppression effect similar to that of the first embodiment is achieved. Can be played.

(Modification)
A modification will be described with reference to FIG. This modification is obtained by reversing the direction of the Zener diode 6 of the overvoltage absorption circuit 5 of FIG. 7, and can provide the same effect.

(Modification)
The intermediate tap 4 may be omitted (with a voltage division ratio of 1), and each Zener diode 6 of the overvoltage absorption circuit 5 may be connected to a terminal of the three-phase armature winding 1.

1 is a circuit configuration diagram of an automotive alternator according to Embodiment 1. FIG. It is explanatory drawing of the voltage clip (limitation) by the surge and Zener diode in the conventional generator. FIG. 3 is a relationship diagram of an output voltage and current of a generator at a predetermined number of revolutions in a conventional generator, and is an explanatory diagram of a clip operating point in FIG. 2. It is explanatory drawing of the load dump surge and clip of an Example. FIG. 5 is a relational diagram between the output voltage and current of the generator at a predetermined number of revolutions in the vehicle AC generator of Example 1, and is an explanatory diagram of the clip operating point in FIG. 4. 6 is a circuit diagram of an automotive alternator according to Embodiment 2. FIG. FIG. 5 is a circuit diagram of an automotive alternator of Example 3. FIG. 10 is a circuit diagram showing a modification of the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Armature winding 2 ... 1st rectifier 3 ... Diode 4 ... Intermediate tap 5 ... Overvoltage absorption circuit 6 ... Zener diode (constant voltage diode) )
7 ... Node 8 ... Field winding 9 ... Regulator 10 ... Output terminal 11 ... Flywheel diode (flywheel current attenuation circuit)
12 ... Zener diode (impedance element, flywheel current attenuation circuit)
13. ..Transistors (flywheel current decay circuits)
14 ..Overvoltage detection terminal ..Time constant reduction signal terminal

Claims (7)

A field winding that excites rotating multipole poles;
An armature winding wound around an armature core disposed opposite to the multipole magnetic pole;
A field current control switching element that performs switching control of a field current that is connected in series to the field winding and is supplied to the field winding;
A full-wave rectifier that rectifies the generated voltage output from each phase winding constituting the armature winding to charge the on-vehicle battery to a predetermined charging voltage Vb;
In a vehicle alternator comprising:
An overvoltage absorption circuit comprising a plurality of constant voltage diodes having a star connection between an intermediate tap provided in each phase winding and a predetermined node and having a breakdown voltage smaller than the charging voltage Vb is provided. A vehicle alternator characterized by the above. In the vehicle alternator according to claim 1,
The vehicle alternator characterized in that the breakdown voltage Vz of the constant voltage diode is set to 0.5 Vb ≦ Vz ≦ Vb with respect to the charging voltage Vb of the in-vehicle battery. The vehicle alternator according to any one of claims 1 to 2 ,
An AC generator for a vehicle, wherein a current density of a constant voltage diode of the overvoltage absorption circuit is set lower than a current density of a diode of the full-wave rectifier. In the vehicle alternator according to claim 1,
The node generator is connected to a cathode electrode of each constant voltage diode and supplies power to the field winding. In the vehicle AC generator according to claim 4 ,
An AC generator for a vehicle having a flywheel diode, an impedance element connected in series with the flywheel diode, and a flywheel current attenuation circuit connected in parallel with the field winding. In the vehicle alternator according to claim 5 ,
The vehicular AC generator, wherein the impedance element includes a constant voltage diode having a cathode electrode connected to a cathode electrode of the flywheel diode. In the vehicle alternator according to claim 5 or 6 ,
An AC generator for a vehicle comprising an impedance element short-circuit transistor connected in parallel with the impedance element.

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