JP2003174798A - Ac generator for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC generator for a vehicle which can attenuate a field current in a short period of time even if it is a field circuit where the time constant is relatively long. <P>SOLUTION: The AC generator 1 for a vehicle comprises an armature winding 2, a rectifier 3, field windings 4 and 5, and a voltage controller 6. The field windings 4 and 5 are wound on field poles, and are arranged coaxially, and the field winding 5 has a time constant shorter than that of the field winding 4. If the slip off or the like of a power cable occurs and the supply of a field current is stopped, the field current in the field winding 5 of a shorter time constant attenuates quickly and becomes zero in a short period of time. Then, both of a reflux diode 6 connected in parallel with the field winding 4 and the field winding 5 work as reflux circuits. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle AC generator mounted on a passenger car, a truck or the like.

[0002]

2. Description of the Related Art Generally, when a power cable connected to an output terminal of an alternator for a vehicle is disconnected or a contact failure occurs, a surge voltage is generated and damages in-vehicle devices or semiconductor parts inside the generator. May be given.

The mechanism of generation of this surge voltage is due to the fact that the power supply is disconnected or the circuit is momentarily cut off to cut off the supply destination of the current and a so-called no-load saturation voltage appears at the output terminal of the generator. . The generation of the no-load saturation voltage continues as long as the field current for exciting the field pole of the generator continues to flow.

Since the vehicle alternator is driven by an internal combustion engine for running the vehicle, it has a very wide range of rotational speeds to be used, and it is necessary to stably supply an output voltage to in-vehicle devices and batteries within the range. Therefore, it is designed to generate a rated voltage at a vehicle idling speed or lower. For example, if the idling speed of the vehicle is 600
In a vehicle in which the rpm and the speed increase ratio are set to 2.5, the rotation speed of the vehicle AC generator at this idling rotation is 1500 rpm, but the vehicle AC generator has a rated voltage at this rotation speed. It is designed to obtain an output current of several tens of amps at 14V. For this reason, the generation start rotational speed of the vehicle alternator, that is, the rated voltage establishment rotational speed is designed to be about 1000 rpm.

In general, a vehicular AC generator is a kind of synchronous generator, so that the voltage induced in the armature increases in proportion to the rotational speed of the field pole. In a vehicle alternator that generates a rated voltage of 14 V at about 1000 rpm, the voltage induced in the armature reaches 280 V at the maximum operating speed of about 20000 rpm, and when the power cable is disconnected, this high voltage is lost. Appears at the output terminal as the load saturation voltage.

In recent vehicle alternators, a technique of constructing a rectifying element of a full-wave rectifier with a Zener diode having a reverse breakdown characteristic is adopted so that such a high voltage is not output to the outside of the generator. There is. However, when a surge voltage occurs in a vehicle AC generator that uses a full-wave rectifier composed of Zener diodes, this energy is not released to the outside, but is converted to thermal energy as reverse-direction power consumption of the Zener diodes. ,
It causes a great deal of thermal damage to the Zener diode.

The conventional voltage control device detects the output voltage of the generator. When the detected output voltage exceeds the reference value, the supply of the field current is stopped to weaken the field flux, and the opposite is detected. When the output voltage is lower than the reference value, the supply of the field current is permitted and the field flux is increased to control the output voltage to converge within a predetermined range. Therefore, if the power cable is disconnected from the output terminal of the vehicle alternator due to an accident or the like and a no-load saturation voltage appears at this output terminal, the supply of the field current is immediately stopped and the field flux is reduced. It has become.

[0008]

However, even if the supply of the field current is stopped, the field winding still has an inductance component, and when the field current is cut off, the inductance component causes an excessive high voltage (magnetic field). (Rapid release of energy), which may damage the voltage control device.
Therefore, a freewheeling diode as shown in FIG. 9 has been conventionally used. The field current is not instantaneously attenuated by the freewheeling diode when the supply is stopped, but is circulated in the closed circuit formed by the field winding and the freewheeling diode, and the thermal energy is generated by the resistance component of the field winding. Is converted to and attenuated.

The current at this time can be obtained as a solution of the following equation when expressed quantitatively. _{V b -V q = L · dI} f / dt + R · I f ( in field supply _{t <t 0) ... (1} ) -V d = L · dI f / dt + R · I f ( field supply stop after t> _{t 0) ... (2) I} f = (I 0 + V d / R) · exp (-R · (t-t 0) / L) -V d / R (t> t 0) ... (3) here , L is the inductance of the field winding, R is the resistance value of the field winding, V _d is the forward voltage drop of the freewheeling diode, and I ₀
Is the field current value immediately before the field supply is stopped, and V _q is the voltage drop when the power transistor for controlling the field current is intermittently closed.

The behavior of the field current after the field supply is stopped is shown in FIG.
As shown by the dotted line b in FIG. 3B, and decays exponentially with the time constant τ = L / R and the final reached value I _final = −V _d / R. But,
Since the freewheeling diode cannot conduct in the reverse direction, the energization is stopped when the current value I (t) = 0. That is,
Even if the power transistor is opened and the field supply is stopped,
Time (=-(L / R) · ln) when I _f = 0 in the equation (3)
During the period corresponding to (V _d / (V _d + R · I ₀ ))), the field current continues to flow and overvoltage continues to be generated.

Particularly, in the recent small-sized and high-output vehicle AC generators, the resistance of the field winding tends to be small and the inductance tends to be large, so that the overvoltage continuation time becomes longer accordingly. The present invention has been made in view of the above circumstances, and an object thereof is to provide an automotive alternator capable of attenuating a field current in a short time.

[0012]

In order to solve the above-mentioned problems, an automotive alternator of the present invention includes a rotor having a plurality of field poles and a first field winding for magnetizing the field poles. The wire and a time constant shorter than that of the first field winding,
A second field winding for magnetizing the field pole, and an armature for inducing an AC voltage by a rotating magnetic field generated by the rotor,
A rectifier that converts the AC output of the armature into a DC, a controller that controls the output voltage by adjusting the field current that flows through the first and second field windings, and the first and second fields. It is connected in parallel with the magnetic winding and includes a circulation circuit for circulating the field current when the supply of the field current is cut off by the control of the control device. When an excessive output voltage is generated due to disconnection of the power cable and the supply of the field current is stopped, the field current flowing through the second field winding having a short time constant is attenuated in a short period of time. The back electromotive force becomes zero. Therefore, after that, the field current flowing through the first field winding flows through the circulation circuit and the second field winding, and the current of opposite polarity flows through the second field winding. It will be. As a result, the interlinkage magnetic flux to the armature is rapidly attenuated, so that the overvoltage state of the vehicle alternator can be eliminated early.

Further, when the above-mentioned free-wheeling circuit has a first circuit composed of one diode and a second circuit provided with an element for promoting attenuation of the field current, these first circuits are provided.
And switching means for switching the second circuit, and the control device switches the switching means to select the second circuit when the output voltage of the rectifier exceeds the reference value, and the first circuit when the output voltage does not exceed the reference value. It is desirable to select the circuit. With this, by switching to the second circuit when the output voltage exceeds the reference value, it is possible to accelerate the attenuation of the field current, and it is possible to significantly reduce the duration of the overvoltage.

Further, it is desirable that the above-mentioned second circuit is constructed by connecting a plurality of diodes in series. By increasing the number of diodes used as a circulation circuit, it is possible to reduce the final value of the field current flowing in this circulation circuit after stopping the supply of the field current, until the field current disappears. The time can be greatly reduced.

When the rectifying element included in the rectifier is a Zener diode, the above-mentioned control device selects the second circuit when the reference value smaller than the reverse breakdown voltage of the Zener diode is exceeded. Is desirable. By configuring the rectifier using the Zener diode, it is possible to suppress surge generation due to reverse breakdown of the Zener diode when a high voltage higher than the Zener voltage is generated and a current flows. Also, by setting the reference value for switching to the second circuit to be equal to or less than this Zener voltage,
When a high voltage exceeding the Zener voltage is generated, the field current can be quickly attenuated to reduce the output voltage, and damage to the Zener diode can be minimized.

Further, it is preferable that the control device described above performs the switching from the first circuit to the second circuit in a state in which a closed circuit including the first and second field windings is formed.
As a result, it is possible to prevent momentary circuit interruption when switching the freewheeling circuit, and to prevent surge voltage caused by momentary interruption of the field current, thus eliminating the need for an excessive protection circuit or the like. Become.

Further, it is desirable that the first and second field windings described above are coaxially arranged. Since the second field winding has a short time constant, it can have a small inductance (a small number of turns) and a large resistance (a small wire diameter). For this reason, the conventional field circuit can be used as it is, and the field winding conventionally used is wound as the first field winding in the vacant space and the second field winding. Since it is possible to wind by adding a wire, the design change can be minimized and the build-up can be suppressed.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A vehicle alternator according to an embodiment of the present invention will be described below in detail with reference to the drawings. [First Embodiment] FIG. 1 is a diagram showing a configuration of a vehicle AC generator according to a first embodiment. As shown in FIG. 1, the vehicle AC generator 1 of the present embodiment is configured to include an armature winding 2, a rectifier 3, field windings 4 and 5, and a voltage control device 6.

The armature winding 2 is a multi-phase winding (for example, a three-phase winding) and is wound around an armature core to form an armature. The AC output induced in the armature winding 2 is the rectifier 3
Is supplied to. The rectifier 3 is a full-wave rectifier circuit that rectifies the AC output of the armature winding 2 into a DC output.
A diode is used as a rectifying element corresponding to each phase.

One of the field windings 4 generates an interlinking magnetic flux required to induce a voltage in the armature winding 2. The field winding 4 is wound around a field pole (not shown) to form a rotor. The other field winding 5 is the field winding 4
It has a time constant shorter than the time constant of, and is coaxially arranged with respect to the field winding 4 and wound around the field pole.

The voltage control device 6 controls the output voltage of the vehicular AC generator 1 within a predetermined range by adjusting the field current flowing through the field windings 4 and 5. To this end, the voltage control device 6 is configured to include a power transistor 61, a freewheeling diode 62, an LPF (low pass filter) 63, and a voltage comparator 64.

The power transistor 61 includes the field winding 4,
5 is connected in series to interrupt the field current. The freewheeling diode 62 is connected in parallel to the field windings 4 and 5 and causes the field current to flow back when the power transistor 61 is opened. The freewheeling diode 62 constitutes a freewheeling circuit. The LPF 63 is for removing high-frequency components of the output voltage of the vehicular AC generator 1, and is composed of, for example, a well-known CR circuit including a resistor and a capacitor. The voltage comparator 64 compares the output voltage Vs of the LPF 63 with a predetermined reference value Vreg1. This reference value Vreg1 is for controlling the output voltage of the vehicle alternator 1, and is set to, for example, 14.5V.

The vehicle alternator 1 of this embodiment has such a structure, and its operation will be described below. In a normal state in which the power cable is securely connected and contact failure does not occur, the output voltage of the vehicle alternator 1 and the predetermined reference value Vreg1 are controlled by the voltage comparator 64 in the voltage control device 6. Be compared. When the output voltage is higher than the reference value Vreg1, the power transistor 61 is opened and the field current flowing through the field windings 4 and 5 is reduced, so that the output voltage is lowered. On the contrary, when the output voltage is lower than the reference value Vreg1, the power transistor 61 is closed and the field current flowing through the field windings 4 and 5 is increased, so that the output voltage is increased. Thus, in the normal state, the output voltage of the vehicular AC generator 1 is controlled so as to converge to the reference value Vreg1.

On the other hand, if the power cable is disconnected from the output terminal B of the vehicular AC generator 1 due to some accident, or if a contact failure occurs between the power cable and the output terminal B (hereinafter, this state will be referred to as "abnormal state"). Since the vehicle alternator 1 performs a power generation operation in a no-load state,
A high voltage is generated at the output terminal B. Of course, since the output voltage at this time is higher than the reference value Vreg1, the power transistor 61 is continuously opened, and the supply of the field current from the power transistor 61 to the field windings 4 and 5 is stopped. It

FIG. 2 is a diagram showing changes in the number of interlinkage magnetic fluxes and field currents in an abnormal state. In FIG. 2, “a” is the number of interlinkage magnetic fluxes of the armature of the vehicle AC generator 1 of the present embodiment, and “b” is the number of interlinkage magnetic fluxes of the armature of the conventional vehicle AC generator. I _f1 ”is the field current of the field winding 4,
“I _f2 ” represents the field current of the field winding 5. Further, FIG. 3 and FIG. 4 are explanatory diagrams of the energization path of the field current in the abnormal state.

In an abnormal state, the power transistor 61
There Once continuously open, its from time t ₀ immediately after up to t _1, the field current flowing through the two field windings 4 and 5 are both decays exponentially (Fig. 2, Fig. 3) . In particular, since the field winding 5 is set to have a short time constant, the field winding 5
The field current flowing through the field decays in a short time.

Assuming that the field current flowing through the field winding 4 is I _f1 and the field current flowing through the field winding 5 is I _f2 , these values between times t ₀ and t ₁ are as follows. become. I _f1 = (I ₀₁ + V _d / R ₁ ) · exp (−R ₁ · (t−t ₀ ) / L ₁ ) −V _d / R ₁ (4) I _f2 = (I ₀₂ + V _d / R _{2 ) · exp (-R 2 · (} t-t 0) / L 2) -V d / R 2 ... (5) where, L ₁ is of the field winding 4 inductance, L ₂ is the field winding 5 , R ₁ is the resistance value of the field winding 4,
R ₂ is the resistance value of the field winding 5, V _d is the forward voltage drop of the freewheeling diode 62, I ₀₁ is the field current value flowing in the field winding 4 immediately before the supply of the field current is stopped, and I ₀₂ Is the value of the field current that was flowing in the field winding 5 immediately before the supply of the field current was stopped.

When the time t ₁ is reached, the field current flowing through the field winding 5 becomes 0, and the counter electromotive voltage of the field winding 5 disappears, so that the current starts flowing in the opposite direction (FIG. 4). ). The source of this current is one of the field windings 4, and after the time t ₁ , the field winding 5 acts as a circulating circuit of the field winding 4. That is, the magnetomotive force in the direction of canceling the field flux generated by the field current flowing in one field winding 4 is generated by the field current flowing in the other field winding 5, and the time t ₁ to t ₂ During the period, the total number of flux linkages to the armature winding 2 is rapidly attenuated. During this period, the counter electromotive voltage generated in the field winding 5 is fixed to the forward voltage V _d of the freewheeling diode 62 because the freewheeling diode 62 is provided side by side. Therefore, the reverse current flowing through the field winding 5 during this period can be represented by V _d / R ₂ .

Thus, at time t₁To t₂In between
Field current I flowing through the field winding 5 _f2Is     I_f2= -V_d/ R₂                                            … (6) Becomes Note that time t₁To t₂Field winding up to
Field current I flowing in line 4 _f1Is the above equation (4)
It is applied as is.

By the way, the interlinkage flux number λ for the armature winding 2 is determined by the field currents I _f1 and I _f of the field windings 4 and 5, respectively.
_{Using f2} , it can be expressed as follows. λ = k ₁ · I _f1 + k ₂ · I _f2 (7) From this equation (7) as well, the field current expressed by the equation (6) flows in the field winding 5, so that the field winding It can be seen that the magnetic flux generated by the field current flowing in 4 is canceled by the magnetic flux generated by the field current flowing in field winding 5, and the magnetic flux interlinking with armature winding 2 is rapidly attenuated.

Further, when the time t ₂ is reached, the counter electromotive voltage enough to turn on the freewheeling diode 62 can no longer be generated in the field winding 4, so that the field current becomes the other field winding 5.
It circulates by itself and disappears immediately. The field currents I _f1 and I _f2 flowing through the field windings 4 and 5 after the time t ₂ are as follows: I _f1 = −I _f2 = I _t2 · exp (− (R ₂ + R ₁ ) · (t−t ₂ ). / (L ₁ + L ₂ )) (8) Where I _t2 is the field winding 4, at time t ₂ .
5 is the value of the field current that was flowing.

As described above, in the vehicle alternator 1 of this embodiment, an excessive output voltage is generated due to the disconnection of the power cable or the like, and the supply of the field current to the field windings 4 and 5 is stopped. Then, the field current flowing through the field winding 5 having a short time constant is attenuated in a short time and the back electromotive force becomes zero. Therefore, after that, the field current flowing through the field winding 4 flows through the freewheeling diode 62 and the field winding 5, and a current having a polarity that cancels the magnetic flux generated in the field winding 4 is applied. It becomes possible to flow to 5. As a result, the interlinkage magnetic flux to the armature is rapidly attenuated, so that it becomes possible to eliminate the overvoltage state of the vehicle alternator 1 at an early stage.

Further, in the vehicle AC generator 1 of the present embodiment, the field winding 5 has a short time constant, so that it can have a small inductance (a small number of turns) and a large resistance (a small wire diameter).
Therefore, the conventional field circuit can be used as it is, and the field winding 5 can be additionally wound in the empty space in which the field winding 4 which has been conventionally used is wound. This makes it possible to minimize the design change and prevent the build-up from increasing.

[Second Embodiment] FIG. 5 is a diagram showing a configuration of a vehicle AC generator according to a second embodiment. As shown in FIG. 5, the vehicle AC generator 1A of the present embodiment includes an armature winding 2, a rectifier 3, field windings 4 and 5, and a voltage control device 6A. This vehicle AC generator 1A is different from the vehicle AC generator 1 shown in FIG. 1 in that the voltage control device 6 is replaced with a voltage control device 6A, and other configurations are basically the same. Common to.

The voltage control device 6A includes a power transistor 61, a freewheeling diode 62, an LPF 63, and a voltage comparator 6.
4, 65, a circulation circuit 66, and switches 67 and 68. The same components as those of the voltage control device 6 shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The voltage comparator 65 compares the output voltage Vs of the LPF 63 with a predetermined reference value Vreg2. This reference value Vre
g2 is set to a value larger than the reference value Vreg1 used in the voltage comparator 64 that controls the intermittent state of the power transistor 61. For example, if the reference value Vreg1 is 14.
At 5V, this reference value Vreg2 is set to 20V.

The circulating circuit 66 is an element that promotes the attenuation of the field current, and is specifically composed of diodes connected in multiple stages. The switches 67 and 68 are switching means for selectively switching between the freewheeling diode 62 as the first circuit and the freewheeling circuit 66 as the second circuit based on the output of the voltage comparator 65. Specifically, when the output of the voltage comparator 65 is low level, that is, the LPF 6
In the normal state in which the output voltage of 3 does not exceed the reference value Vreg2, only the switch 67 connected in series to the freewheeling diode 62 is closed to select the freewheeling diode 62. On the other hand, when the output of the voltage comparator 65 is high level,
That is, in an abnormal state in which the output voltage of the LPF 63 exceeds the reference value Vreg2, only the switch 68 connected in series to the circulation circuit 66 is closed and the circulation circuit 66 is selected.

The vehicle alternator 1A of this embodiment has such a structure, and its operation will be described below. In a normal state in which the power cable is securely connected and contact failure does not occur, the output of the voltage comparator 65 maintains a low level, so that the switch 67 is closed and the freewheeling diode 62 is selected. Therefore, the operation of the voltage control device 6A is the same as the operation of the voltage control device 6 shown in FIG. 1, and the output voltage of the vehicular AC generator 1A is controlled so as to converge to the reference value Vreg1.

On the other hand, if the power cable comes off from the output terminal B of the vehicular AC generator 1A due to some accident, or if a contact failure occurs between the power cable and the output terminal B, an abnormal condition occurs in the vehicular AC generator. Since the machine 1A performs a power generation operation in a no-load state, a high voltage is generated at the output terminal B. When this high voltage becomes higher than the reference value Vreg1,
The power transistor 61 is continuously open,
The supply of the field current from the power transistor 61 to the field windings 4 and 5 is stopped.

FIG. 6 is a diagram showing changes in the interlinkage magnetic flux and the field current in the abnormal state. In FIG. 6, “a” indicates the number of interlinkage magnetic fluxes of the armature of the vehicle AC generator 1A of the present embodiment, and “b” indicates the number of interlinkage magnetic fluxes of the armature of the conventional vehicle AC generator. ing. When the output voltage of the vehicle AC generator 1A exceeds the reference value Vreg2 in an abnormal state, the output of the voltage comparator 65 changes from the low level to the high level. When the output of the voltage comparator 65 becomes high level, the switch 68 is closed and the switch 67 is opened, and the connection from the freewheeling diode 62 to the freewheeling circuit 66 is switched.

By the way, the circulation circuit 66 of the present embodiment is
Since it is configured by connecting diodes in multiple stages, compared to the case where one free-wheeling diode 62 is used,
Forward voltage n times (n is the number of diodes connected in multiple stages)
Can be Therefore, the final reaching value of the field current can be greatly reduced, and the high voltage state can be eliminated early by promoting the attenuation of the field current. Although the voltage across the freewheeling circuit 66 increases as the number of series stages of the diodes forming the freewheeling circuit 66 increases, the back electromotive force of the field winding 4 is reduced due to the attenuation of the field current flowing through the field winding 4. The voltage also decays. At this time, when the counter electromotive voltage generated by the field current of the opposite polarity flowing through the field winding 5 and the counter electromotive voltage generated in the field winding 4 have the same magnitude (time t ₄ ), this counter electromotive voltage is applied to the diode. Even if it has not reached the forward voltage drop (n · V _d ), the field current flowing through the field winding 5 turns around and decays. That is, it acts to dramatically attenuate the number of flux linkages in the period from time t ₃ to time t ₄ .

Assuming that the field current flowing through the field winding 4 is I _f1 'and the field current flowing through the field winding 5 is I _f2 ', the current flows through the field winding 5 from time t ₀ when the abnormality occurs. Field current I _f2 '
The values of these field currents until the time t ₃ when becomes 0 are as follows. I _f1 ′ = (I ₀₁ + n · V _d / R ₁ ) · exp (−R ₁ · (t−t ₀ ) / L ₁ ) −n · V _d / R ₁ (9) I _f2 ′ = (I _{02 + n · V d / R} 2) · exp if _{(-R 2 · (t-t} 0) / L 2) reaches the _{-n · V d / R 2 ...} (10) time t _3, the field winding 5 Field current flowing through
Then, since the counter electromotive voltage of the field winding 5 disappears, a current starts flowing in the opposite direction. The source of this current is one of the field windings 4, and after the time t ₃ , the field winding 5 acts as a circulation circuit of the field winding 4. That is, the magnetomotive force in the direction of canceling the field flux generated by the field current flowing in one field winding 4 is generated by the field current flowing in the other field winding 5, and from time t ₃ to t _4. During the period, the total number of flux linkages to the armature winding 2 is rapidly attenuated. During this time,
The counter electromotive voltage generated in the field winding 5 increases until the forward voltage n · V _d of the entire circulation circuit 66 is reached because the circulation circuit 66 is provided side by side. Therefore, the final value of the reverse current flowing through the field winding 5 during this period is n
- it can be represented by V _d / R _2.

Specifically, time t₃To t_FourIn between
Field current I flowing through the field winding 5 _f2’     I_f2’= (N · V_d/ R₂) ・ Exp (− (R₁+ R₂) ・ (T-t₃)                     / (L₁+ L₂))-N ・ V_d/ R₂              … (11) Becomes Note that time t₃To t_FourField winding up to
Field current I flowing in line 4 _f1′ Is the equation (9) above.
It is applied as it is.

The interlinkage magnetic flux number λ for the armature winding 2 can be expressed as follows by using the field currents I _f1 'and I _f2 ' of the field windings 4 and 5, respectively. λ = k1 · I _f1 ′ + k2 · I _f2 ′ (12) From this equation (12) as well, the field current represented by the equation (11) flows into the field winding 5, so that the field winding It can be seen that the magnetic flux generated by the field current flowing in 4 is canceled by the magnetic flux generated by the field current flowing in field winding 5, and the magnetic flux linked to armature winding 2 is rapidly attenuated. Particularly, unlike the case of the first embodiment, from time t ₃ to.
Since the current value I _f2 'of the field winding 5 at t ₄ becomes large, the offsetting amount (k2 · I) of the interlinkage magnetic flux based on this field current
_f2 ') can be increased.

Further, time t_FourWhen it reaches
A back electromotive force that makes the circuit 66 conductive is applied to the field winding 4.
Since it cannot occur, the field current is only in the other field winding 5.
It circulates and disappears immediately. Time t_FourField winding
Field current I flowing in lines 4 and 5_{f 1}’I_f2’     I_f1’= -I_f2’= I_t4・ Exp (-(R₂+ R₁) ・ (T-t_Four)                                   / (L₁+ L₂)) … (13) Becomes Where I_t4Is time t_FourAt field winding 4,
5 is the value of the field current that was flowing.

As described above, in the vehicle alternator 1A of the present embodiment, the number of diodes used as the circulating circuit 66 is increased so that the field current flowing in the circulating circuit 66 after the supply of the field current is stopped. It is possible to reduce the final value of the current, and it is possible to greatly reduce the time until the field current disappears.

Further, the vehicle AC generator 1A of the present embodiment
Now, by using the switches 67 and 68, the freewheeling diode 62 is
And the free-wheeling circuit 66 are switched, it is possible to reduce the overvoltage continuation time at the time of a system abnormality such as disconnection of the power cable while maintaining the stability of the voltage control when the system is normal without disconnection of the power cable. Can be realized. That is, from the viewpoint of the stability of the output voltage, it is preferable that the time constant of the freewheeling circuit is long. Therefore, when the system is normal, the freewheeling diode 62 is used to circulate the field current. Further, in order to accelerate the decay of the field current and the interlinkage magnetic flux generated due to this at the time of system abnormality, it is preferable that the time constant of the circulation circuit is short. Therefore, the circulation circuit 66 in which diodes are connected in multiple stages is used The field current is circulated.

The present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in each of the above-described embodiments, each rectifying element included in the rectifier 3 is composed of a diode, but each rectifying element may be composed of a Zener diode. As a result, the rise of the output voltage when an abnormality occurs can be suppressed to the reverse breakdown voltage (Zener voltage) of the Zener diode or less, and the voltage control devices 6, 6
Damage to various control circuits (not shown) in A can be reduced.

Further, when the rectifier 3 included in the vehicle alternator 1A of the second embodiment described above is constructed by using the Zener diode, the reference value Vre of the voltage comparator 65 is obtained.
It is desirable to set g2 below the Zener voltage. For example, when the Zener voltage Vz is 20V, the reference value Vreg2
Is set to 18V. As a result, when the output voltage of the vehicle alternator 1A exceeds the Zener voltage when an abnormality occurs, the freewheeling diode 62 has already been switched to the freewheeling circuit 66, so that the heat generated by the Zener diode forming the rectifier 3 is minimized. Can be suppressed.

Further, in the vehicle alternator 1A of the second embodiment described above, the freewheeling diode 62 to the freewheeling circuit 6 are used.
When switching to 6, the switches 67 and 68 connected in series to each other were switched at the same time. However, this switching can be performed with a closed circuit including the field windings 4 and 5 being temporarily formed. desirable.

For example, with the power transistor 61 in the voltage control device 6A closed for a short time, the switch 67,
Switch 68. As a result, it is possible to prevent momentary circuit interruption when switching the freewheeling circuit, and to prevent surge voltage caused by momentary interruption of the field current, thus eliminating the need for an excessive protection circuit or the like. Become.

In the second embodiment described above, a plurality of diodes are connected in series to form a freewheeling circuit. However, as shown in FIG. 7, one normal diode 75 and one Zener diode 76 are arranged in opposite directions. They may be connected in series to form a freewheeling circuit. By doing so, there is an advantage that the semiconductor chip size can be reduced.

FIG. 8 is a diagram showing a modification of the voltage control device. The voltage control device 6B shown in FIG. 8 differs from the voltage control device 6A shown in FIG. 5 in that a voltage comparator 69 for setting the intermittent state of the switch 68 is added. The voltage comparator 69 compares the output voltage Vs of the LPF 63 with a predetermined reference value Vreg3. This reference value Vreg3 is set to a value slightly smaller than the reference voltage Vreg2 used in the voltage comparator 65. For example, the reference value Vreg2 is 2
At 0V, this reference value Vreg3 is set to 19V. Therefore, when an abnormal state such as disconnection of the power cable occurs and the output voltage of the vehicle alternator becomes high, the output of the voltage comparator 69 first changes to a high level, and immediately after that, the voltage comparator 69. The output of 65 changes to high level. Therefore, the two switches 67 and 68 are temporarily
Are closed at the same time, and then switch 67 with a slight time difference.
Is opened. In this way the two switches 67, 6
Even when the switching of 8 is performed, a closed circuit including the field windings 4 and 5 can be temporarily formed. This allows
Since it is possible to prevent momentary circuit interruption and prevent surge voltage generated due to momentary interruption of the field current, an excessive protection circuit or the like becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a vehicle AC generator according to a first embodiment.

FIG. 2 is a diagram showing changes in interlinkage magnetic flux and field current in an abnormal state.

FIG. 3 is an explanatory diagram of a conduction path of a field current in an abnormal state.

FIG. 4 is an explanatory diagram of a conduction path of a field current in an abnormal state.

FIG. 5 is a diagram showing a configuration of a vehicle AC generator according to a second embodiment.

FIG. 6 is a diagram showing changes in interlinkage magnetic flux and field current in an abnormal state.

FIG. 7 is a diagram showing a modified example of the freewheeling circuit.

FIG. 8 is a diagram showing a modification of the voltage control device.

FIG. 9 is an explanatory diagram of a conventional energization path of a field current.

[Explanation of symbols] 1,1A AC generator for vehicles 2 armature winding 3 rectifier 4, 5 field winding 6, 6A, 6B voltage control device 61 Power transistor 62 freewheeling diode 63 LPF (low pass filter) 64, 65, 69 voltage comparator 66 circulation circuit 67, 68 switch

Continued front page    F-term (reference) 5H590 AA01 AA03 AB01 CA07 CA23                       CC01 CC18 CC24 CC28 CC34                       CD01 CE05 DD25 DD77 EA07                       EA13 EB02 EB21 FA06 FB01                       FC17 FC21 FC22 FC23 FC26                       GA02 GA06 HA02 HA05 JA19                       JB06 JB09 JB15

Claims (6)

[Claims] 1. A rotor having a plurality of field poles, a first field winding for magnetizing the field pole, and a time constant shorter than a time constant of the first field winding. ,
A second field winding for magnetizing the field pole; an armature for inducing an AC voltage by a rotating magnetic field generated by the rotor; a rectifier for converting an AC output of the armature into a DC; And a control device for controlling the output voltage by adjusting the field current flowing through the second field winding, and the control device connected in parallel with the first and second field windings. A recirculation circuit that circulates the field current when the supply of the field current is cut off by the control of 1. The vehicle AC generator. 2. The recirculation circuit according to claim 1, further comprising: a first circuit including one diode, and a second circuit including an element that promotes attenuation of the field current. The control device further includes switching means for switching between the first and second circuits, and the control device switches the switching means to select the second circuit when the output voltage of the rectifier exceeds a reference value, An alternator for a vehicle, wherein the first circuit is selected when it does not exceed. 3. The vehicle alternator according to claim 2, wherein the second circuit is configured by connecting a plurality of diodes in series. 4. The rectifying element included in the rectifier according to claim 2 or 3, wherein the rectifying element is a Zener diode, and the control device is configured to operate when the reference value smaller than a reverse breakdown voltage of the Zener diode is exceeded. An alternator for a vehicle, wherein the second circuit is selected. 5. The control device according to claim 2, wherein the control device closes the switching from the first circuit to the second circuit by including the first and second field windings. An alternator for vehicles, characterized in that the operation is carried out with the circuit formed. 6. The vehicle alternator according to claim 1, wherein the first and second field windings are coaxially arranged.