Electricity: single generator systems – Automatic control of generator or driving means – Voltage of generator or circuit supplied
Reexamination Certificate
2001-08-07
2003-09-16
Dougherty, Thomas M. (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Voltage of generator or circuit supplied
C322S017000
Reexamination Certificate
active
06621251
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is based on and claims priority from Japanese Patent Applications 2000-239918 filed Aug. 8, 2000 and 2001-144937, filed May 15, 2001, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle AC generator and a voltage regulator thereof.
2. Description of the Related Art
Although a field coil is not supplied with field current, an armature winding of a vehicle AC generator generates a small output voltage signal if a rotor of the generator rotates because of residual magnetic flux of pole cores mounted in the rotor. U.S. Pat. No. 5,376,876 discloses a voltage regulator in which terminal voltage of an armature winding of an AC generator is compare with a staircase wave-form to detect rotation of the rotor.
If leak current flows from the outside of a high DC potential into the armature winding while the field coil is not supplied with field current, the output terminal of the armature winding is biased by the high DC potential. Accordingly, the output voltage of the armature winding is too high to be compared with the staircase wave-form, and the comparator does not provide a normal output signal as long as the leak current flows into the armature winding.
In order to solve the above problem, WO99/07064 proposes an AC generator in which the output voltage of an armature winding is compared with a variable threshold value of a window comparator to detect rotation of a rotor.
However, if leak current flows into the armature winding from the outside of a high DC voltage, it is impossible to know the level of the DC voltage because contact resistance is not fixed and widely changes. It is necessary, but impossible to provide an infinite number of threshold levels to detect a signal of the leak current.
Mechanism of the DC biasing when the leak current flows is discussed below with reference to
FIGS. 8-14
.
Firstly,
FIG. 8
schematically shows a case in which leak current flows into a Z-phase winding for generating phase voltage Pz that is not used as a rotation signal. If contact resistance between the output terminal of the Z-phase winding and +B potential of, for example a positive cooling fin of the full-wave rectifier is R
1
and contact resistance between the output terminal of the Z-phase winding and a ground, for example a housing is R
2
, the contact resistances R
1
and R
2
changes widely according to foreign material such as salt water, mud water, or its dried product, crystals, rust or the like.
FIG. 9
shows an equivalent circuit diagram when leak current flows. The potential or terminal voltage Pz of the terminal of the Z-phase winding is expressed as follows: Vbatt·R
2
/(R
1
+R
2
). Since the amounts of the resistances R
1
and R
2
are not fixed, the potential Pz of the terminal is not fixed.
When an engine is started and the rotor of the AC generator is rotated, the terminal of the Z-phase winding is applied a voltage that alternates and changes according to rotation speed of the rotor from a value expressed by Vbatt·R
2
/(R
1
+R
2
). (as shown in FIG.
10
).
In WO99/07064, although the threshold value of the window comparator is variable, only a limited number of threshold values are provided. It takes a time to detect all the variable DC bias voltage signals, and it is too late when the signal is found to correspond to one of the threshold values that were provided. Therefore, it is impossible to make the AC generator generate power concurrently when the engine starts.
Further, if leak current flows into a Y-phase winding for generating phase voltage Py that is detected and used for the rotation signal, as shown in
FIG. 11
(or equivalent circuit is shown in FIG.
12
), the potential thereof is fixed to the value expressed by Vbatt·R
2
/(R
1
+R
2
). As a result, it is impossible to detect the potential of other X and Z-phase windings unless the voltage Px or Pz becomes higher than Vbatt or lower than the ground voltage. That is, if the generated voltage is lower than the DC bias voltage, the generated voltage levels of the X-phase and Z-phase windings are masked by the DC bias voltage (as indicated by broken lines in FIG.
13
). Therefore, it takes a delay time &tgr; to detect the generated voltage. (as shown in FIG.
13
).
The delay time &tgr; becomes the longest when the DC bias voltage becomes as high as a half of the terminal voltage of the vehicle battery, as hereafter described in more detail.
If the DC bias voltage becomes lower than a half of the terminal voltage of the vehicle battery, in other words, if the contact resistance R
1
is larger than the contact resistance R
2
, the voltage Px or Pz of the X-phase or Z-phase winding alternately changes, with the DC bias voltage applied to the Y-phase winding being the center of the amplitude. If the voltage of the bias voltage is lower than a half of the battery terminal voltage, the phase voltages Px and Pz become the ground voltage faster than they become the battery terminal voltage. If the Z-phase voltage Pz becomes the ground voltage, a diode connected to the Z-phase winding passes signal current i
1
, so that the signal voltage becomes higher than the bias voltage. If the phase voltage Px becomes the ground voltage, a diode connected to the X-phase winding, likewise, passes signal current, as shown in FIG.
13
A.
On the other hand, if the DC bias voltage is higher than a half of the terminal voltage of the vehicle battery, in other words, if the contact resistance R
1
is smaller than the contact resistance R
2
, the phase voltage Px or Pz alternately changes, with the bias voltage being the center of the amplitude. If the bias voltage is higher than a half of the battery terminal voltage, the phase voltages Px and Pz become the battery terminal voltage faster than they become the ground voltage. If the phase voltage Px becomes the battery terminal voltage, a diode connected to the X-phase winding passes signal current i
2
, so that the signal voltage becomes lower than the bias voltage, as shown in FIG.
14
A.
Therefore, if the bias voltage applied to the Y-phase winding becomes as high as a half of the battery terminal voltage due to leak current, it takes the longest time for the phase voltages Px and Pz of the X-phase and Y-phase windings to become 0 V or the battery terminal voltage. That is, if an amount of the leak current is very large, it takes a long time to generate the rotation signal to be detected.
JP-A-3-215200 and PCT National Publication 8-503308 disclose control circuits in which terminal voltages of two phase windings are detected to thereby detect leak current. However, it is necessary to insert two terminals of the armature winding into the control circuit, which may become complicated in structure and increase in the number of joints of wires, resulting in lowering the reliability of the control circuit.
In the control circuit disclosed in JP-A-3-215200, a voltage difference between the terminals of two phase windings is detected in a voltage level that floats from the ground. Therefore, it is necessary to provide a specific comparator with a complicated supply source if such a floating voltage is to be compared with a reference voltage. Moreover, when the alternator starts generation, excessively high voltage may be applied to the comparator. Therefore, it is necessary to provide various protecting means for the comparator, resulting in a large size of the control circuit.
SUMMARY OF THE INVENTION
The present invention is to provide a voltage regulator of a vehicle AC generator that can surely detect a voltage signal from a terminal of a multi-phase armature winding.
In order to attain the above object, a voltage regulator of a vehicle AC generator according to a main feature of the invention includes means for detecting phase voltage of an armature winding, and a comparator for comparing phase voltage with a variable threshold level signal that varies according to the phase voltage. Even if leak c
Ogino Toshiyo
Tanaka Koji
Taniguchi Makoto
Cuevas Pedro J.
Denso Corporation
Dougherty Thomas M.
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