Current generating system

A generator comprises an output winding connected to input terminals of a full-wave rectifier and a field winding. A resistor and diodes are also connected to the input terminals for supplying voltage to a voltage regulator. The generator, the rectifier and the voltage regulator are assembled together within a generator housing, so that a single conducting wire is sufficient for connecting the generator and a battery. The pole cores of the generator are made of low carbon steel the residual magnetism of which has been increased by a cementation process or by insertion of high carbon steel elements.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a current generating system for a motor 
vehicle, and more particularly to a generator driven by an engine for 
supplying a battery of a motor vehicle and other electrical loads. The 
generator is generally a three-phase alternating current generator 
equipped with a voltage regulator for controlling the output voltage of 
the generator. 
2. Brief Description of Prior Art 
In a typical conventional current generating system of this kind, many 
conducting wires are used for electrical connections between the 
generator, the battery charged thereby and the voltage regulator for 
controlling the output voltage of the generator. Such a system is subject 
to a wire disconnection, a terminal disengagement, an incorrect connection 
at connectors etc., whereby the generator stops generating current, the 
output voltage at the generator may not be controlled and so on. 
In another conventional system, which is of the type comprising a generator 
which establishes an initial field excitation by residual magnetism, a 
rotor, and especially pole cores therefor, must be made of a material 
having a high-residual magnetism, for example high carbon steel or the 
like. 
However, since the pole cores for the rotor are generally produced through 
cold forging of a low-carbon steel in view of productivity, manufacturing 
cost, etc., it is almost impossible to produce pole cores from the 
high-carbon steel by such a conventional method. On the other hand, when 
the pole cores are made of high-carbon steel through other mechanical 
treatments, such problems as decrease of productivity and a large increase 
in cost are encountered. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
current generating system to overcome the above disadvantages. 
It is another object of the present invention to provide a current 
generating system which has less conducting wires between a generator, a 
battery and a voltage regulator. 
It is a further object of the present invention to provide a current 
generating system which has pole cores made of a low-carbon steel, a 
surface of which is subjected to a cementation treatment to thereby 
increase the residual magnetism without a large increase in cost. 
It is a further object of the present invention to provide a current 
generating system in which a bobbin for holding a field winding is made of 
a low-carbon steel, a surface of which is subject to a cementation 
treatment to thereby increase the residual magnetism without a large 
increase in cost. 
It is still a further object of the present invention to provide a current 
generating system which has pole cores made of a low-carbon steel, in 
which some bars made of a high-carbon steel are inserted, to increase 
residual magnetism without a large increase in cost. 
These and other objects of the present invention will become more apparent 
by reference to the following detailed description when considered in 
connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, numeral 1 designates a direct current power source 
of an alternating current generator equipped with a rectifying device, 
which is driven by an engine (not shown) on a motor vehicle to supply 
battery charging current and other electrical loads on the vehicle. The 
generator 1 includes a three-phase Y-connected output winding 2 which is 
connected to AC input terminals 4a, 4b and 4c of a three-phase full-wave 
rectifying network 4. The network 4 comprises three positive diodes 4f 
constituting a positive terminal 4d at their cathodes and three negative 
diodes 4g likewise constituting a negative terminal 4e at their anodes. 
The positive terminal 4d is connected to a single output terminal 6 of the 
generator 1. 
A resistor 7 and diodes 8 and 9 are respectively connected to the AC input 
terminals of the rectifying network 4 for constituting a signal terminal A 
producing an output signal (voltage) earlier than the positive termminal 
4d because of provision of the resistor 7. 
The generator also includes a field winding 3 and a voltage regulator 5 for 
controlling the field excitation at the field winding 3. The voltage 
regulator 5 includes a resistor 10, a zener diode 11 and a resistor 12, 
which are connected in series with each other, forming a voltage 
responsive circuit 13 connected to the signal terminal A. The regulator 5 
also includes a first transistor 14, a second transistor 15, a capacitor 
16, a resistor 17 and a diode 18. The base of the first transistor 14 is 
connected with the voltage responsive circuit 13 so that the conduction 
and non-conduction of the transistor 14 is controlled by the voltage drop 
developed across the resistor 12 responding the voltage at the signal 
terminal. A capacitor 16 is connected in parallel with the zener diode 11 
and the resistor 12 for smoothing the output voltage at the terminal A. 
The collector of the transistor 14 is connected to the terminal A through 
the resistor 17 and the emitter thereof is grounded. The base of the 
transistor 15 is connected to the collector of the transistor 14 and 
collector-emitter path thereof is connected across the positive and 
negative terminals 4d and 4e of the rectifier network 4 through the field 
winding 3 forming a field energizing circuit, so that the field excitation 
is controlled by the transistor 15. The diode 18 is connected across the 
field winding 3 for absorbing the back electromotive force produced 
thereat when the field current is cut off. 
The voltage regulator 5 is assembled within a housing of the generator 1 so 
that the single output terminal 6 is sufficient for charging a battery 19 
through a cable 23. 
An electrical load 21 such as a headlamp, radio or the like, and a 
voltmeter 22 connected in parallel therewith, are connected to the battery 
19 through a key switch 20. 
In operation, when the key switch 20 is closed so as to start an engine 
(not shown), the generator 1 begins to be rotated causing the output 
winding 2 to generate a small voltage due to residual magnetism of the 
generator 1, produced by pole cores of a rotor for carrying the field 
winding 3, irrespective of the fact that no field excitation is 
established at the field winding 3 since the transistor 15 remains 
turned-off at the starting of the engine. 
The small voltage at that time is converted into direct current by the 
combination of the negative diodes 4g of the rectifier network 4, resistor 
7 and diodes 8 and 9, which is applied to the base of the transistor 15 as 
well as the voltage responsive circuit 13. 
As the circuit 13 detects the voltage at the terminal A at that time, which 
is insufficient to drive the first transistor 14 into conduction, the 
second transistor 15 is driven into conduction to establish an initial 
field excitation. The amount of current flowing through the field winding 
3 is relatively small at the initial field excitation, because the output 
voltage at the terminal A caused by the residual magnetism is small. 
However, the generator 1 soon generates a sufficient output voltage, 
because of the initial field excitation, so at to drive the second 
transistor 15 into a full conduction, resulting in a completion of the 
field excitation. 
The output at the generator 1 then charges the battery 19 through the cable 
23 and at the same time the voltage at the signal terminal A is applied to 
the voltage responsive circuit 13 including the capacitor 16. When the 
voltage across the capacitor 16 exceeds a predetermined value, the circuit 
13 drives the first transistor 14 into conduction and thereby drives the 
second transistor 15 into nonconduction. Thus the supply of the field 
current for the field winding 3 is stopped to decrease the output voltage 
at the generator 1. 
On the other hand, when the voltage across the capacitor 16 falls below the 
predetermined value, the first transistor 14 is restored to its initial 
state of nonconduction, and likewise the second transistor 15 becomes 
conductive to again establish the field excitation, thus increasing the 
output voltage at the generator 1. 
Repeating the above operation, the battery voltage is consequently 
controlled at a desired value. 
The generator described above can generate the output voltage at a earlier 
stage of the rotational operation of the generator when compared with such 
a generator having a diode in place of the resistor 7 and the same 
construction for the remaining parts, since the combination of the 
resistor 7 and the diodes 8 and 9 can effectively apply even a small 
voltage (for example 2.about.3 volts) at the generator 1 to the base of 
the second transistor 15. 
More in detail, the base current for the second transistor 15 is determined 
by the respective resistance values of the resistors 7 and 17 and the 
voltage drop (around 0.6 volt) across the base and the emitter of the 
second transistor 15. When the resistor 7 is replaced by a diode, the base 
current for the second transistor 15 is further limited by the voltage 
drop of 0.8 volt across the diode, resulting in the decrease of the 
voltage applied to the base of the second transistor. In other words, with 
the diode in place of the resistor 7, the second transistor 15 remains 
turned-off until the rotational speed of the generator reaches a higher 
level compared with that of the embodiment shown in FIG. 1. 
According to the experimental results, the generator can start to generate 
the output voltage at 4,000 to 5,000 rpm with the diode in place of the 
resistor 7, and the generator according to the present invention begins to 
generate the output voltage at a generator speed of 2,000 to 3,000 rpm. 
According to the above embodiment, the voltage regulator 5 is assembled 
within the generator housing, so that conducting wires will not be 
required therebetween when mounted in an engine room. Thus, troubles, such 
as a disconnection between the voltage regulator and the generator, may be 
reduced. 
FIG. 2 shows a rotor for a generator in cross-section. 
Numerals 24 and 25 designate a pair of pole cores being magnetized 
oppositely with respect to one another when the field winding 3 enclosed 
therein is energized. The pole cores 24 and 25 are made of a low-carbon 
steel through cold-forging and are respectively provided with a plurality 
of fingers 24b and 25b at outer peripheries and center bosses 24a and 25a, 
whereby each of the pole cores forming a U-configuration in cross-section. 
The fingers 24b and 25b project alternately towards the respective 
opposite pole cores 24 and 25 at their outer peripheries. 
A rotary shift 26 is inserted into central bores of the pole cores 24 and 
25 and placed at a serrated portion to rotate the cores together. 
The field winding 3 is wound on a coil bobbin 30, which is interposed 
between the pole cores 24 and 25, and is connected to a slip-ring 28 on 
the shaft 26. The inner surface of the coil bobbin 30 is coated with an 
insulating layer 31 for the purpose of insulation between the bobbin 30 
and the field winding 3. 
The coil bobbin 30 is made of a low-carbon steel by a press-forming and 
being subjected to a cementation treatment. 
Accordingly, the pole cores 24 and 25 with the bobbin 30 can provide a 
sufficient residual magnetism for the voltage generation of the generator. 
The coil bobbin may be subjected to a quenching treatment as occassion 
demands after the cementation treatment. 
Thee coil bobbin may be also subjected to the cementation treatment only at 
the outer surface thereof, while the inner surface may be formed with 
copper-plating for preventing the inner surface from cementation. The 
copper-plating is also advantageous in that it facilitates adhesive 
strength of the insulating layer of epoxy resin etc. thereon. 
FIG. 3 shows a modified rotation in cross-section, wherein the same 
reference numerals designate the same or equivalent parts in the 
embodiment shown in FIG. 2. 
The field winding 3 is wound on a bobbin 27 made of an insulating material 
and interposed between the pole cores 24 and 25. 
The cores 24 and 25 are provided with a plurality of holes 24c and 25c 
through which a plurality of rods 29 made of a high-carbon steel are 
inserted, and the thus-formed pole cores provide a sufficient residual 
magnetism for use during starting of the engine, as described above. 
The cross-sections of the hole and rod are not limited to a circular 
configuration, but they may be an arcuate configuration. 
Additionally, the hole may be formed with a closed extremity. 
FIG. 4 shows a modified pole core in cross-section. 
The pole core 24 shown in FIG. 4 is produced through the following steps. 
The pole core is covered with a copper-plating layer 25 at its surface for 
avoiding cementation. The copper-plating layer 25 at the inner surface of 
the fingers 24b is cut away, and the portion of the inner surface is 
subjected to a cementation treatment. 
The cementation treatment may be, of course carried out on all the surfaces 
of the pole core, and also the pole core may be subjected to a quenching 
treatment after the cementation treatment.