Current generating system with output winding switching device

A first and a second full-wave rectifying network are respectively connected with both ends of generating coils of a generator for respectively generating alternating current thereat. A switching device has normally closed contacts for making voltage differences among the input terminals of the second full-wave rectifying network zero, whereby the coils act as a star-connected current generating winding so long as the contacts are held closed. The switching device also has an energizing coil for actuating the normally-closed contacts to open when the rotational speed of the generator exceeds a predetermined value. When the normally-closed contacts are opened, the coils no longer act as the star-connected winding but an independently generating winding, to thereby increase the output current from the generator even when the generator operates at a relatively high rotational speed. A terminal circuit having a resistor and diodes connected with input terminals of the first full-wave rectifying network supplies base current for a switching transistor of a voltage regulator so that the voltage regulator establishes a separate field excitation at an earlier stage of the rotational speed of the generator.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a current generating system, and more 
particularly to the system having a self-excitation alternating current 
generator used in a motor vehicle for supplying electric power to a 
battery, electric loads such as lamps and so on. 
(2) Description of Prior Art 
It is recently required for a generating system used in a motor vehicle to 
produce sufficient electric energy during whole operating conditions of 
the engine mounted in the vehicle, namely at a low speed operation as well 
as a high speed operation of the engine. 
In this respect, it is known that electrical connections of poly-phase 
current generating windings of the generator are changed in response to 
the operating conditions thereof to obtain higher electric energy. For 
example, in a separate excitation generator of three-phase current 
generating type, the windings are arranged as three-phase Y-connected 
windings at the low speed operation while the windings are changed to 
operate as respective independent generating windings at the high speed 
operation, as it is disclosed in a U.S. Pat. No. 4,024,456 granted to the 
present inventors. 
On the other hand, it is a problem of a current generating system having a 
self-excitation generator that a rotational speed of the generator, where 
it begins to generate an output of alternating current, is higher than 
that of the separate excitation generator. In a conventional 
self-excitation generator, a rotor of the generator, especially pole cores 
thereof are made of a material such as having a high residual magnetism, 
or number of winding turns of an armature is increased, in order to 
decrease the rotational speed of the generator where it begins to generate 
the output. 
However, even though the material having the high residual magnetism is 
used for the pole cores, or special treatments are employed for the pole 
cores to increase the residual magnetism thereof, there exists a limit of 
the rotational speed decrease. Accordingly, the rotational speed of the 
self-excitation generator where the generator begins to generate the 
output is still higher than that of the separate excitation generator. 
In addition when the number of winding turns is increased to increase the 
output energy at the low-speed operation of the generator, the output 
energy thereof is contrariwise decreased during the high-speed operation, 
with a result that the effective charging for a battery can not be 
obtained during the high-speed operation. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an improved 
generating system to overcome the above drawbacks. 
It is another object of the present invention to provide an improved 
generating system of the type in which the electrical connections of the 
generating windings are changed in response to the operating conditions to 
obtain the sufficient output energy at low speed operation as well as 
high-speed operation. 
It is a further object of the present invention to provide a generating 
system having a self-excitation generator which enables to decrease the 
number of rotational speed of the generator where it begins to generate 
the output, and thereby establishes a separate field excitation at an 
earlier stage of the rotational speed of the generator. 
It is a still further object of the present invention to provide an 
improved generating system which is low in cost, simple in construction, 
reliable in use and so on. 
These and other objects of the present invention will be seen by reference 
to the drawings, taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a three-phase alternating current generator G, 
which is driven by an engine (not shown), includes a three phase 
generating winding 2 having three generating coils 2a, 2b, and 2c and a 
field winding 3. A first full-wave rectifying network 4 includes three 
positive diodes 4a, 4b and 4c, three negative diodes 4d, 4e and 4f, a 
first positive direct current output terminal 4g connected with respective 
cathodes of the positive diodes, and a first negative direct current 
output terminal 4h connected with the respective anodes of the negative 
diodes, which is grounded. 
Each one end of the three generating coils 2a, 2b and 2c is respectively 
connected with AC input terminals of the respective pairs of the positive 
diodes 4a, 4b and 4c and the negative diodes 4d, 4e and 4f, designated at 
a, b and c. 
A second full-wave rectifying network 5 likewise includes three positive 
diodes 5a, 5b and 5c, three negative diodes 5d, 5e and 5f, a second 
positive direct current output terminal 5g connected with the respective 
cathodes of the positive diodes, and a second negative direct current 
output terminal 5h connected with the respective anodes of the negative 
diodes. Each other end of the three generating coils 2a, 2b and 2c is 
likewise respectively connected with AC input terminals of the respective 
pairs of the positive diodes 5a, 5b and 5c and the negative diodes 5d, 5e 
and 5f designated at d, e and f. 
The first and second positive direct current output terminals 4g and 5g are 
connected with each other through a conductor 32 and so are the first and 
second negative direct current output terminals 4h and 5h through a 
conductor 33. 
A terminal circuit 40 having diodes 8 and 9 and a resistor 10 forms a third 
positive direct current output terminal A, where a direct current is 
appeared when the generates G begins to generate the output. Each one end 
of the diodes 8 and 9 and the resistor 10 is connected with the AC input 
terminals a, b and c of the first full wave rectifying network 4, while 
the other ends are connected to the terminal A. 
A voltage regulator 6 includes a voltage responsive circuit 14 connected to 
the third positive terminal A for responding the output voltage of the 
generator G. The circuit 14 comprises voltage dividing resistors 11 and 13 
and a zener diode 12. The regulator 6 also includes a capacitor 17 
connected across the zener diode 12 and the resistor 13 for smoothing the 
output voltage from the terminal A. The voltage responsive circuit 14 need 
not be always connected to the terminal A, but may be, of course, 
connected to the first positive terminal 4g of the first rectifying 
network 4 as indicated by a dotted line in the drawings. 
The regulator 6 also includes a first transistor 15, a second transistor 
16, a resistor 18 and a flywheel diode 19 to proceed a switching operation 
for the field winding 3 in accordance with a potential applied to the 
circuit 14. The base of the first transistor 15 is connected with the 
voltage responsive circuit 14 so that the conduction and non-conduction of 
the first transistor 15 is controlled by the voltage drop developed across 
the resistor 13 which responds to output voltage at the terminal A. The 
collector-emitter path of the first transistor 15 is connected across the 
terminal A and the ground through the resistor 18, and the collector 
thereof is also connected to the base of the second transistor 16 so that 
the terminal A supplies the base current for the second transistor and the 
conduction or non-conduction of the second transistor 16 is controlled by 
the first transistor 15. The collector-emitter path of the second 
transistor 16 is connected in series with the field winding 3 of the 
generator G to form a field excitation circuit, one of which is connected 
to the output terminal of the generator G or another power supply source 
such as a battery 28, wherein the flywheel diode 19 is connected across 
the field winding 3. 
A switching device 29 of a control circuit 20 comprises an energizing coil 
30 and normally closed contacts 31a, 31b, 31c and 31d, wherein fixed 
contacts 31a, 31b and 31c are respectively connected to the AC input 
terminals d, c and f of the second rectifying network 5 while the movable 
contact 31d normally closes the contacts 31a to 31c with each other and is 
energized by the energizing coil 30 to open the contacts 31a to 31d when 
the coil 30 is energized. 
When the contacts 31a to 31d are closed, voltage differences among the 
input terminals d, e and f of the second rectifying network 5 are made 
zero, whereby the generating coils 2a to 2c act as a Y-connected winding. 
On the other hand, when the contacts 31a to 31d are opened, voltage 
differences are appeared among the input terminals d, e and f and those 
voltage differences are derived from the second full-wave rectifying 
network 5 as direct current. Accordingly, the generating coils 2a to 2c 
act as independent alternating generating windings when the contacts 31a 
to 31d are opened. 
The control circuit 20 for controlling the energization of the coil 30 
comprises a voltage detecting means 24 having a resistor 21 and a zener 
diode 22 connected to the terminal A for detecting the output voltage at 
the terminal A. The control circuit 20 also comprises a transistor 23 
having a base connected to the voltage detecting means 24 and a 
collector-emitter path connected to a source of current through the 
energizing coil 30 of the switching device 29, so that when the output 
voltage at the terminal A exceeds a zener voltage of the zener diode 22 
the transistor 23 is made conductive and thereby the coil 30 is energized 
to open the contacts 31a, 31b and 31c. The source of current for the coil 
30 is the terminal c in the present embodiment, however it may be, of 
course, the battery 28, the output terminal 4g of the generator G or the 
like. The voltage detecting means 24 is connected to the terminal A in the 
above embodiment for detecting the output voltage of the generator G, 
however, it may be also connected to the terminal 4g or the battery 28. 
The generator G, the first and second rectifying networks 4 and 5, the 
voltage regulator 6, the control circuit 20, the switching device 29 and 
the terminal circuit 40, which are already described above, are all 
embedded in a generator housing designated by numeral 1, so that one 
terminal 7 is derived from the generator housing 1 and is connected to the 
battery 28 through a conductor 27. 
Numeral 25 designates an ignition key switch and numeral 26 designates an 
electrical load connected to the battery 28 through the key switch 25. 
An operation of the current generating system of the embodiment just 
described will be explained below. Since the switching device 29 normally 
closes the contacts 31a to 31d, the three generating coils 2a to 2c form a 
star-connected (three-phase Y-connected) output winding at the beginning 
of generating the output. When the generator G starts to rotate by the 
engine (not shown), the generator G, more particularly the star-connected 
generating coils 2a to 2c begin to generate the output of the alternating 
current by the residual magnetism of the generator G. The alternating 
current is rectified by means of the diodes 8 and 9 and the resistor 10 of 
the terminal circuit 40 as well as the negative diodes 4d to 4f of the 
first rectifying network 4, so that the alternating current is converted 
into direct current to produce a voltage potential at the terminal A. Here 
it should be noted that since the terminal circuit 40 includes two diodes 
8 and 9 and the resistor 10, the voltage potential is produced at the 
terminal A earlier than that produced in a case where the terminal circuit 
40 consists of three diodes in place of the diodes 8 and 9 and the 
resistor 10. As above, the small voltage potential is produced at the 
terminal A by the residual magnetism and it is then applied to the base of 
the transistor 16 of the voltage regulator through the resistor 18. The 
resistance value of the resistor 18 is so determined that the second 
transistor 16 is driven into conduction (an active state) by the base 
current from the terminal A when the running speed of the engine reaches 
an idling speed thereof. When the transistor 16 becomes active an initial 
field excitation for the generator G is established from the battery 28 
through a field energizing circuit comprising the conductor 27, the field 
winding 3 and the active collector-emitter path of the transistor 16. This 
initial field excitation is not maximum for the field excitation since the 
second transistor 16 is not saturated because of the small base current. 
With the initial field excitation, however, the generator G increases the 
output energy with the increase of the voltage potential at the terminal A 
of the circuit 40, whereby the active state of the transistor 16 is 
enhanced to its saturated (conductive) state. With the saturation of the 
transistor 16, a full field excitation for the generator G is established 
from the battery 28 through the field energizing circuit, and then the 
generator G operates in a normal condition, that is, the generator G 
increases the output energy as the engine speed increases as shown in FIG. 
3. 
A curve O.sub.1 in FIG. 3 shows a characteristic curve of the output 
current from the generator G in the above condition where the generating 
winding 2 act as the three-phase Y-connected output winding. The axis of 
abscissa in FIG. 3 represents a rotational speed N of the generator G (or 
the engine) while the longitudinal axis representing the output current 
from the generator G. 
As seen from FIG. 3, the output current according to the curve O.sub.1 
sharply rises to become sufficient to charge the battery and the 
electrical loads at a relatively low speed operation (the rotational speed 
of N.sub.1), however the rising rate of the output current becomes smaller 
as the rotational speed of the generator increases. Namely, the output 
current produced from the generator with the star-connected winding is 
sufficient to charge the battery at the relatively low speed operation but 
insufficient at the relatively high speed operation. 
When the output voltage at the terminal A exceeds a predetermined value, 
the zener diode 22 is made conductive to drive the transistor 23 into 
conduction. With the conduction of the transistor 23, electric current 
flows through the energizing coil 30 from the terminal c of the first 
network 4 to open the switch 29 with a result that the contacts 31a to 31c 
are separated from each other. 
When the switch 29 is opened the generating coils 2a, 2b and 2c operate as 
independent generating coils, so that the alternating output current 
produced at the respective coils 2a to 2c is subjected to the full-wave 
rectifying operation at the first and second full-wave rectifying networks 
4 and 5. For example, when the voltage appears at the generating coil 2a 
being positive at one end a and negative at the other end d, current flows 
through the diode 4a, the positive direct current terminal 4g, the 
conductor 27, the battery 28 the negative direct current terminal 4h, the 
conductor 33 and the diode 5d. When the voltage polarity is reversed at 
the generating coil 2a, current flows through the diode 5a, the positive 
direct current terminal 5g, the conductor 32, the positive direct current 
terminal 4g, the conductor 27, the battery 28 and the diode 4d. Thus, the 
alternating current produced at the generating coil 2a is subjected to the 
full-wave rectifying operation carried by the diodes 4a and 4d of the 
first rectifying network 4 and the diodes 5a and 5d of the second 
rectifying network 5, and the alternating current produced at the other 
two phase coils 2b and 2c is likewise subjected to the full-wave 
rectifying operation respectively carried by the diodes 4b, 4e, 5b and 5e 
and the diodes 4c, 4f, 5c and 5f, to thereby charge the battery 28 and 
supply the electrical load 26 with the output direct current. 
As in the above operation, the output current characteristics obtained in 
the full-wave independently rectifying operation becomes similar to that 
obtained from the delta-connected generating winding, which is indicated 
by a curve O.sub.2 in FIG. 3. 
According to the curve O.sub.2, the output current from the generator G 
rises at the rotational speed of N.sub.2 higher than N.sub.1, becomes 
equal to the output current I.sub.e of the curve O.sub.1 at the rotational 
speed of N.sub.e and becomes higher than that of the curve O.sub.1 above 
the rotational speed of N.sub.e as seen in FIG. 3. The maximum output 
current I.sub.2 of the curve O.sub.2 is almost 1.7 times as high as that 
I.sub.1 of the curve O.sub.1. 
According to the present embodiment, the normally closed contacts 31a to 
31d of the switch 29 is so arranged as to open its contacts when the 
output at the terminal A exceeds the predetermined value that is, when the 
rotational speed of the generator exceeds the predetermined value of 
N.sub.e, whereby the generating coils 2a, 2b and 2c act as three-phase 
Y-connected generating winding during the rotational speed of the 
generator G being below the speed N.sub.e and they act as three-phase 
independent generating winding during the rotational speed being above the 
speed N.sub.e, thus to obtain the sufficient output energy during the 
whole operational conditions of the generator. 
During the above operation, the voltage regulator 6 operates as follows 
irrespective of the opened or closed condition of the switch 29. The 
voltage responsive circuit 14 responds the output voltage of the 
generator, more particularly the voltage appeared at the terminal A in the 
embodiment, so that when the voltage across the resistor 13 exceeds a 
desired level the first transistor 15 is made conductive causing the 
second transistor 16 in a non-conductive state by removing the base 
current therefor. Accordingly, the field excitation is stopped to decrease 
the output energy of the generator G. Then, the voltage developed across 
the resistor 13 becomes lower than the desired level to drive again the 
first transistor 15 into non-conduction, and thereby the second transistor 
16 is made conductive due to the base current from the terminal A through 
the resistor 18 to establish the field excitation again. Repeating the 
above conduction and non-conduction of the second transistor 16 makes it 
possible to regulate the output voltage of the generator G at a desired 
constant value. 
Referring next to FIG. 2 showing another embodiment of the present 
invention, wherein the same reference numerals are used to designate the 
same or equivalent parts as that of FIG. 1, different construction and 
operation of the embodiment are principally explained hereinafter. 
Additional diodes 34 and 35 are respectively connected between the first 
and second full-wave rectifying networks 4 and 5, in such a manner that 
the cathode of the diode 34 is connected with the first positive terminal 
4g, the anode thereof with the second positive terminal 5g, the anode of 
the diode with the first negative terminal 4h and the cathode thereof with 
the second negative terminal 5h. 
The switch 29 comprises one movable contact 31d and two normally-closed 
fixed contacts 31a and 31b. The contact 31a is connected to the cathode 
sides of the diodes 5a to 5c of the second network 5, while the contact 
31b is connected to the anode sides of the diodes 5d to 5f, so that when 
the contacts 31a and 31b are closed with each other through the movable 
contact 31d the generating coils 2a to 2c act as three-phase Y-connected 
winding. On the other hand, when the contacts 31a and 31b are separated 
from each other the generating coils 2a to 2c act as three independent 
generating windings. The other construction and operation of the 
embodiment shown in FIG. 2 is almost the same as that of FIG. 1. 
In the above embodiments, other poly-phase alternating current generator 
can be also employed in place of the three-phase alternating current 
generator.