Vehicle AC generator

Details Vehicle AC generator Vehicle AC generator

2000-07-27

2002-08-13

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

Reexamination Certificate

active

06433455

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a vehicle AC generator having a Landor rotator.
FIG. 7
to
FIG. 11
show a configuration of a vehicle AC generator in the prior art,
FIG. 7
is a sectional view of the generator,
FIG. 8
is a perspective view of a rotor,
FIG. 9
is a perspective view of a stator,
FIG. 10
is a perspective view of a stator core, and
FIG. 11
is an illustrative view of a relationship between the rotor cores and the stator core. In
FIG. 7
,
1
denotes a front bracket;
2
, rear bracket; and
3
, a stator put between the front bracket
1
and the rear bracket
2
. As shown in
FIG. 7
,
FIG. 9
, and
FIG. 10
, the stator
3
consists of a stator core
4
, and a three-phase stator coil
5
inserted in a slot
4
a
of the stator core
4
.
In FIG.
7
and
FIG. 8
,
6
is a rotor which fixed onto a rotation axis
7
whose both ends are supported by the front bracket
1
and the rear bracket
2
. The rotor
6
comprises a first rotor core
8
, a second rotor core
9
, a field coil
10
wound between both rotor cores
8
and
9
, fans
11
,
12
provided on the back surfaces of both rotor cores
8
and
9
, a pulley
13
provided on the outside of the rotation axis
7
on the front bracket
1
side, and a slip ring
14
provided on the inside of the rotation axis
7
on the rear bracket
2
side to supply a current to the field coil
10
. Then,
15
denotes a brush for supplying a current to the slip ring
14
;
16
, a brush holder for holding the brush
15
;
17
, a rectifier for rectifying the AC output of the stator coil
5
; and
18
, a regulator for controlling the output voltage of the stator coil
5
by adjusting the current of the field coil
10
.
Also, as shown in FIG.
8
and
FIG. 11
, a plurality of almost trapezoidal pole pieces
8
a
,
9
a
whose width is reduced toward a tip portion in the rotation direction are formed on the first rotor core
8
and the second rotor core
9
respectively so as to oppose to an inner diameter surface of the stator core
4
. Thee pole pieces
8
a
,
9
a
are arranged to engage alternatively via a predetermined clearance, and magnetized alternatively to the N pole and the S pole. In addition, in order to suppress the electromagnetic sound by smoothing the magnetic flux distribution in the air gap, chamferings
8
b
,
9
b
are provided on corner portions between outer surfaces of the pole pieces
8
a
,
9
a
opposing to the stator core
4
and both end surfaces in the rotation direction.
In the vehicle AC generator constructed as above in the prior art, the rotor
6
is driven by the internal combustion engine via pulley
13
while the current is supplied from a battery (not shown) mounted in the vehicle to the field coil
10
via the brush and the slip ring
14
, the rotor
6
generates a rotating magnetic field, then the three-phase AC voltage is generated in the stator coil
5
by this rotating magnetic field, and then this voltage is rectified by the rectifier
17
to be supplied lo a load (not shown).
In this manner, when the generator is in the running state and the load is composed or a resistance load, an output current of the generator can be expressed by the following equation.
I=KBD
×1
/L/{l
+[(
R+r
)/&ohgr;
L
]
2
}
½
  (1)
where K is a constant, B is a magnetic flux density in an air gap, D is an outer diameter of the rotor
6
, l is a conductor length of the stator coil
5
, L is a self-inductance of the stator coil
5
, R is a resistance value of the load, r is a resistance value of the stator coil
5
, and &ohgr; is an angular velocity of the rotating magnetic field.
In Eq. (1), parameters other than the angular velocity &ohgr; are decided based on design specifications of the generator and load conditions. Then, if the number of revolution of the generator, i.e., &ohgr; is increased, the output current characteristic exhibits the saturation characteristic because of the influence of the reactance &ohgr;L which is also Increased together with &ohgr;. The current Is in this saturation state can be expressed by
Is∝BD
×1
/L
  (2)
Accordingly, it is understood that, in order to increase the output current at the time of high speed rotation of the generator, i.e., the saturation current Is to obtain the higher output, the magnetic flux density B, the diameter D of the rotor , and the conductor length l of the stator coil
5
must be increased and also the self-inductance L of the stator coil
5
rust be reduced.
However, in order to decrease the inductance L, the number of turns of the stator coil
5
must be reduced. But this is not effective in increasing the output current because such reduction results in reduction of the conductor length l of the stator coil
5
at the same time. In order to increase the output while avoiding the increase in sire of the generator, i.e., without the change of the D in above Eq. (2), there is no way to increase the magnetic flux density D. However, in such generator, tile magnetic flux density B in the loaded condition is extremely reduced rather than the magnetic flux density B in no load condition because of the armature reaction caused by the output current Is. Therefore, the increase of the magnetic flux density B in the loaded condition, i.e., the suppression of the armature reaction is the necessary condition to increase the output current of the generator.
Further, in the low speed revolution of the generator, the corresponding number of revolution is needed to increase the generation voltage up to a predetermined value (battery voltage), and also the output cannot be obtained unless the exciting current value flowing into the field coil
10
is compensated. Therefore, the output current of the generator does not rise unless the number of revolution comes up to the predetermined number of revolution. Since the number of revolution required for the rising of the output current is in inverse proportion to the generated voltage of the stator coil
5
, the generated voltage of the stator coil
5
must be increased to lower the rising number of revolution required for the output current in the low speed revolution. The generated voltage E can be expressed by
E∝Blv=Bl&ohgr;D
/2  (3)
As given in Eq. (3), the magnetic flux density B must also be increased to improve the output characteristic in the low speed revolution. Here the magnetic flux density B corresponds to the magnetic flux density in the air gap formed between the pole pieces
8
a
,
9
a
in the magnetic path indicated by the magnetic flux &PHgr; in FIG.
7
and the stator core
4
. Thus, the reduction of the magnetic reluctance in the air gap leads to the increase of the output in the low speed revolution.
Since the vehicle AC generator is driven by the internal combustion engine at a predetermined speed increasing ratio, the available range of the number of revolution extends from 0 to 18,000 rpm. In particular, the improvement of the output characteristic is requested in the neighborhood of the number of revolution of the generator of about 1,500 rpm, which corresponds to the idling number of revolution of the internal combustion engine, and the number of revolution of the generator of about 6,000 rpm, which corresponds to the normal running state of the vehicle. Because the number of revolution at which the above output current Is becomes the saturation state is about 5,000 rpm, such configuration must be employed as the generator that importance of the increase of the output current Is in the saturation state and the increase of the output current in the idling operation by lowering the number of revolution at the rising of the output current are considered.
To increase the magnetic flux density B in the air gap, as described above, is necessary for the reduction of the number of revolution of the rising output current, i.e., the improvement of the output characteristic in the low speed revolution. This increase can be attained by reducing the magnetic reluctance in the air ga

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