U.S. patent application number 09/893417 was filed with the patent office on 2002-01-03 for vehicle alternator.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Okuno, Tomoya, Tanaka, Koji, Taniguchi, Makoto.
Application Number | 20020000791 09/893417 |
Document ID | / |
Family ID | 18694492 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000791 |
Kind Code |
A1 |
Taniguchi, Makoto ; et
al. |
January 3, 2002 |
Vehicle alternator
Abstract
Shift means shifts a rotation speed range to a low rotation
speed side based on an electricity amount related to rotation
speed. In the rotation speed range, driving torque of a generator
is suddenly changes as a result of an increase of duty ratio of a
switch due to a shortage of generation capacity caused by a
reduction of a rotation speed of a vehicle alternator. Preferably,
the shift means shifts the rotation speed range to the low rotation
speed side by changing the adjust voltage based on the electricity
amount related to rotation speed while the rotation speed is
reduced.
Inventors: |
Taniguchi, Makoto;
(Kariya-city, JP) ; Okuno, Tomoya; (Nishio-city,
JP) ; Tanaka, Koji; (Anjo-city, JP) |
Correspondence
Address: |
Pillsbury Winthrop LLP
1600, Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
DENSO CORPORATION
|
Family ID: |
18694492 |
Appl. No.: |
09/893417 |
Filed: |
June 29, 2001 |
Current U.S.
Class: |
322/28 |
Current CPC
Class: |
Y02T 10/92 20130101;
H02P 9/04 20130101; H02J 7/1446 20130101 |
Class at
Publication: |
322/28 |
International
Class: |
H02H 007/06; H02P
009/00; H02P 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2000 |
JP |
2000-195905 |
Claims
What is claimed is:
1. An alternator for a vehicle, comprising: an AC generation
section having a rotor including a plurality of field poles and
driven by a vehicle engine, a field coil for magnetizing said field
poles, an armature including an armature coil and arranged facing
said field poles of said rotor; a rectifying means for rectifying
AC voltage generated by said armature coil to DC voltage and
charging an electricity accumulating means; a rotation speed
detecting means for detecting an electricity amount related to
rotation speed of said rotor; and a voltage control unit including
a comparing section for comparing an electricity amount related to
the DC voltage with a predetermined adjust voltage and a switch
connected in series to said field coil, said voltage control unit
converging the DC voltage to the adjust voltage by intermittently
controlling said switch based on a compared result of said
comparing section, wherein said voltage control unit includes a
shift means for shifting a rotation speed region to a low rotation
speed side based on the electricity amount related to rotation
speed, and within the rotation speed region, driving torque of the
alternator suddenly changes as a result of an increase of duty
ratio of said switch due to a shortage of generation capacity
caused by a reduction of the rotation speed.
2. An alternator according to claim 1, wherein said shift means
shifts the rotation speed region to the low rotation speed side by
changing the adjust voltage based on the electricity amount related
to rotation speed.
3. An alternator according to claim 2, wherein said shift means
changes the adjust voltage in accordance with a change of the
electricity amount related to rotation speed.
4. An alternator according to claim 2, wherein said shift means
changes the adjust voltage in accordance with the electricity
amount related to rotation speed within a predetermined range of
the electricity amount related to rotation speed and within a
predetermined range of the adjust voltage, said shift means sets an
upper limit of the adjust voltage corresponding to an upper limit
of the electricity amount related to rotation speed, and said shift
means sets a lower limit of the adjust voltage corresponding to a
lower limit of the electricity amount related to rotation
speed.
5. An alternator according to claim 4, wherein said shift means
continuously changes the adjust voltage in accordance with the
electricity amount related to rotation speed within the
predetermined range of the electricity amount related to rotation
speed.
6. An alternator according to claim 5, wherein said shift means
changes the adjust voltage in accordance with the electricity
amount related to rotation speed within a predetermined control
delay time.
7. An alternator according to claim 6, wherein the control delay
time is set to 0.1 seconds or less.
8. An alternator according to claim 4, wherein said shift means
step-wisely changes the adjust voltage in accordance with the
electricity amount related to rotation speed within a predetermined
range of the electricity amount related to rotation speed.
9. An alternator according to claim 4, wherein the rotation speed
corresponding to the upper limit of the electricity amount related
to rotation speed is set larger than a rotation speed corresponding
to a vehicle engine idling speed.
10. An alternator according to claim 9, wherein the rotation speed
corresponding to the upper limit of the electricity amount related
to rotation speed is set to 1.5-2 times of a predetermined
generation start rotation speed.
11. An alternator according to claim 4, wherein the rotation speed
corresponding to the lower limit of the electricity amount related
to rotation speed is set larger than a predetermined generation
start rotation speed.
12. An alternator according to claim 4, wherein the lower limit of
the adjust voltage is approximately equal to an open terminal
voltage of said electricity accumulating means or larger than the
open terminal voltage by a predetermined voltage.
13. An alternator according to claim 4, wherein the upper limit of
the adjust voltage is set to continuous service voltage when the
vehicle normally runs.
14. An alternator according to claim 2, wherein said rotation speed
detecting means detects the electricity amount related to rotation
speed based on a fundamental frequency of a one-phase output
voltage of said armature coil.
15. An alternator according to claim 14, further including a
low-pass filter for extracting a low-pass component of an output
voltage of said rotation speed detecting means.
16. An alternator according to claim 1, wherein said rotation speed
detecting means converts frequency information included in an
output voltage of said armature coil into voltage signal.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2000-195905 filed on Jun.
29, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an alternator suitable for
use in a vehicle.
[0004] 2. Description of Related Art
[0005] A rotation speed during an idling state (hereinafter,
referred to as idling engine speed) of a vehicle has a tendency to
be set low in order to protect terrestrial environment such by
decreasing exhausting gas and reducing an amount of fuel
consumption. For example, there is such a vehicle that the idling
engine speed thereof is set to around 550 rpm.
[0006] In a low friction engine like this, when the idling engine
speed is reduced, a slight disturbance causes a flutter of an
engine rotation speed. That is, a hunting phenomenon occurs because
the engine is extraordinarily sensitive to the reduction of the
rotation speed.
[0007] A mechanism of the hunting phenomenon will be explained in
more detail.
[0008] FIG. 8 shows a relationship between rotation speed of a
generator and torque required for driving thereof (hereinafter,
referred to as driving torque). A curved line A1-C1 indicates a
driving torque characteristic while a constant generation load is
applied. A curved line A2-C2 indicates a driving torque
characteristic while a constant generation load slightly larger
than the constant generation load described above is applied.
Points C1 and C2 indicate lower limit of the rotation speed and the
driving torque for allowing the alternator to generate an output
more than a required load. Consumption torque (load torque) of the
alternator is suddenly changed at the points C1 and C2, and becomes
the disturbance cannot be negligible for an engine. When the
alternator is moved to lower rotation side than the points C1 and
C2, since a current supply to a vehicle load cannot be satisfied by
only output power of the alternator, a vehicle battery compensates
the electric power.
[0009] For example, in a current supply state of a continuous
service load (electric load required at least in term of vehicle
operation such as ignition, drive of fuel injection valve, and
driving power of control computer thereof) an engine becomes a
stabilized state at point A1 in a range of the idling engine speed.
At this time, when additional electric load, for example, a small
light or the like is applied, an output of the alternator is
increased by increasing in an exciting current. As a result, the
driving torque of the alternator is increased, and an operational
point moves from the point A1 to point A2. At this time, an engine
only injects fuel to become the stabilized state in the point A1, a
feedback control of fuel injection for an engine is remarkably
delayed. Therefore, the rotation speed of the engine is reduced,
and the operational point moves to point B after all. As the
rotation speed is reduced, the driving torque for driving the
alternator is increased, so that the operational point furthermore
continues the lowering below the point B.
[0010] At this time, a feedback control system of fuel injection
immediately detects the lowering of the rotation speed, and
increases the amount of fuel injection for the purpose of
maintaining the operational point to the point A2. However, since
it takes a certain time from the fuel injection through an
explosion thereof and conversion thereof into torque, thereby
introducing remarkable control delay after all as described
above.
[0011] Due to this control delay, the operational point drops to
point D, discharge from the battery is caused. In a short while,
the feedback control of the fuel injection for the engine starts to
operate and the rotation speed transfers from the lowering to an
uprising, while the alternator charges the battery in order to
compensate a discharged capacity of the battery occurred at the
previous time. At this time, the alternator has to output a total
current of a current required by the electric load of the vehicle
and charging current of the battery, and the operational point
moves on a curved line D-E-F via point E by increasing the driving
torque in an acceleration manner.
[0012] After a while, when the operational point reaches point F
and a charge to the battery is finished, since output current of
the alternator is reduced to a required electric load of the
vehicle. Thus, the driving torque is also abruptly reduced and the
operational point moves on a curved line F-G. At this time, the
engine increases fuel for the purpose of increasing the rotation
speed reduced to the point D. However, when the operational point
exceeds the point F, the load torque of the engine is abruptly
decreased. Thus, the rotation speed of the engine is increased in
an acceleration manner, and the operational point is moved upwardly
to point G. Thus, the feedback control system of the fuel injection
detects the uprising of the rotation of the engine, and tries to
control for the purpose of maintaining the operational point to the
point A2 by reducing the amount of fuel injection. However, due to
fluctuation of the driving torque and the control delay of the
alternator, the engine rotation speed is fluctuated in a range of
N1 through N2, and repeats hunting. FIG. 9 shows a timing chart
showing the hunting phenomenon.
[0013] The hunting of the rotation speed of the alternator is
improved by restraining the discharge of the battery by mounting a
large output alternator. However, an adoption of the large output
alternator is not easy viewing from a mounting space, cost, and a
noise.
[0014] For inhibiting the hunting, JP-A-54-7111 discloses a method
of adjusting the driving torque by controlling an output voltage
corresponding to a speed differential of the alternator.
JP-B2-6-55040 discloses a method for increasing an adjusting
voltage while maintaining a delay of predetermined time with
respect to the uprising of the rotation speed of an engine.
JP-A-7-123796 discloses a method for detecting an application of
the electric load, lowering the adjust voltage for a moment, and
thereafter, the adjust voltage is gradually returned to the
original state thereof.
[0015] However, in JP-A-54-7111, the control is started after the
rotation speed starts to rise due to delay in the detection of a
first drop of the rotation speed, so that a convergence of the
hunting takes a lot of time, or it is resulted in an engine stop at
the worst situation when the drop of the rotation speed is large.
Further, according to the present method, an exciting current (or
duty ratio) is controlled in order to properly control the output
voltage of the alternator to a predetermined voltage. However,
since the output voltage of the alternator connected to the battery
depends on a state of the battery not on the exciting current, the
control of the output voltage is not easy. For example, the output
voltage of the alternator on a curved line A2-C2 charges the
battery by generating power more than the open terminal voltage of
the battery. However, when the rotation speed is reduced and the
operational point is reduced under the point C2, the battery starts
to discharge, and the terminal voltage of the battery continues to
decrease in order to cancel out polarization obtained by the
charge. At this time, the adjust voltage of the alternator is set
at a constant value, so that the alternator itself cannot control
the output voltage. Therefore, the output voltage depends on the
terminal voltage of the battery. When the operational point resides
on a curved line D-F, the dependence on the battery is the
same.
[0016] In the method of the JP-B2-6-55040, the adjust voltage is
changed in a considerably wide range from the idling engine speed
to the maximum rotation speed. Viewed from paying attention to only
the idling state, the battery voltage hardly changes. Therefore,
the charge and discharge of the battery causing the hunting cannot
be prevented. If the change of the adjust voltage is made large in
the vicinity of the idling engine speed, the battery voltage in the
maximum rotation speed becomes higher than necessary voltage, and
the high voltage of the battery not only promotes a reduction in
battery electrolyte and a decrease of battery life span, but also
results in a deviation from a voltage range for appropriate
operation of each device in the electric system.
[0017] According to the method of JP-A-7-123796, the application of
electric load is detected, and the adjust voltage is reduced for a
moment and is gradually returned to the original state. In this
method, there arises the following disadvantage.
[0018] That is, in this method, in order to detect the application
of the electric load only during engine idle without the delay, any
signals to inform the application of the electric load from the
vehicle must be received, and it becomes difficult to take a
countermeasure within the alternator. An electrical system for a
vehicle becomes complicated and expensive as in JP-A-6-343300.
SUMMARY OF THE INVENTION
[0019] An object of the present invention is to provide a vehicle
alternator reducing and smoothening the fluctuation of driving
torque thereof, so that the hunting of the rotation speed is
suppressed during an engine idle.
[0020] According to the present invention, an AC generation section
has a rotor including a plurality of field poles and driven by a
vehicle engine, a field coil for magnetizing the field poles, an
armature including an armature coil and arranged facing the field
poles. A rectifying means rectifies AC voltage generated by the
armature coil to DC voltage and charges an electricity accumulating
means. A rotation speed detecting means detects an electricity
amount related to rotation speed of the rotor. A voltage control
unit includes a comparing section for comparing an electricity
amount related to the DC voltage with a predetermined adjust
voltage and a switch connected in series to the field coil. The
voltage control unit converges the DC voltage to the adjust voltage
by intermittently controlling the switch based on a compared result
of the comparing section. The voltage control unit includes a shift
means for shifting a rotation speed region to a low rotation speed
side based on the electricity amount related to rotation speed.
Within the rotation speed region, driving torque of the alternator
suddenly changes as a result of an increase of duty ratio of said
switch due to a shortage of generation capacity caused by a
reduction of the rotation speed.
[0021] Thereby, a inflection point of a fluctuation of the engine
rotation speed is forcibly moved, within an engine idling range, to
rotation speed further lower than a lower limit to which an engine
rotation speed drops, so that engine load torque is smoothly
changed. Here, the engine rotation speed drop is caused by an
increase of the driving torque (load torque viewed from engine) of
the vehicle alternator particularly when an electric load is
applied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Additional objects and advantages of the present invention
will be more readily apparent from the following detailed
description of preferred embodiments thereof when taken together
with the accompanying drawings in which:
[0023] FIG. 1 is a schematic view showing a block diagram of a
control unit of the present invention;
[0024] FIG. 2 is a schematic view showing a circuit diagram of an
adjust voltage generating device;
[0025] FIG. 3 is a graph showing a relationship between adjust
voltage and rotation speed in the control unit;
[0026] FIG. 4 is a timing chart showing states of respective
sections in the control unit;
[0027] FIG. 5 is a timing chart showing an operational of the
control unit;
[0028] FIG. 6 is a graph showing a relationship among output
current, driving torque and output voltage of a vehicle
alternator;
[0029] FIG. 7 is a graph showing a relationship between adjust
voltage and rotation speed (modification)
[0030] FIG. 8 is a graph showing a relationship between rotation
speed and driving torque in a conventional control unit (prior
art), and
[0031] FIG. 9 is a timing chart showing operations of respective
sections in the conventional control unit (prior art).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0032] (First Embodiment)
[0033] FIG. 1 is a block diagram showing a voltage control unit of
a vehicle alternator 1.
[0034] The vehicle alternator 1 is driven by a pulley mounted on a
crankshaft of the engine through a belt, and the alternator 1 is
mounted around the engine. Electric power generated by the
alternator 1 is stored in a battery 2. Electric current is supplied
from battery 2 and the alternator I into an electric load device 3
through a switch (not illustrated) when a load is applied.
[0035] The alternator 1 includes an armature coil 11. Here,
although the most general symmetric 3-phases coil is illustrated as
an example, the number of phases is optional. A diode type full
wave rectifier 12 converts the AC power generated by the armature
coil 11 into DC power. A field coil 13 is wound around a rotor core
(not illustrated) including a plurality of field poles. A voltage
control unit 14 controls a DC output voltage generated by the
alternator 1 to a predetermined voltage by adjusting a field
current flowing in the field coil 13.
[0036] Resistor elements 141, 142 form a resistance dividing
voltage circuit for dividing an AC voltage (generated voltage) of
one phase output terminal of the armature coil 11. A frequency
detecting device 143 detects a fundamental frequency of the divided
AC voltage described above. Here, a F/V converter is adopted as the
frequency detecting device 143. A low-pass filter 144 extracts a DC
voltage composed of low-range components of output voltage of the
frequency detecting device 143. Here, a CR low-pass filter is used.
An adjust voltage generating device 147 converts the DC voltage
described above to an adjust voltage command value output from the
low-pass filter 144. Resistor elements 146 form a second resistance
dividing voltage circuit for dividing a voltage of the battery 2. A
comparator 148 compares the divided voltage of the battery voltage
with the adjust voltage command value output from the adjust
voltage generating device 147. A power transistor 149 works as a
switch in the present invention and is driven by an output voltage
of the comparator 148. The power transistor 149 is connected in
series to the field coil 13. The power transistor 149 may be formed
as a high side switch configuration. A circulating diode 145
circulates a field current when the power transistor 149 is turned
off. Numeral 150 denotes a base current limit resistor.
[0037] Details of the adjust voltage generating circuit 147 will be
explained hereinafter with reference to FIG. 2.
[0038] An output voltage 1475 of the low-pass filter 144 is a DC
voltage proportioned to rotation speed of a rotor.
[0039] A plurality of diodes 1471 are connected in series, and
output a lower limit of the adjust voltage command value by forming
a constant voltage circuit together with a resistor element 1472.
An anode of the highest potential of the diode group 1471 is
connected to a battery potential (B potential) through the resistor
element 1472, and a cathode of the lowest potential is grounded.
Since the diode group 1471 is formed of two steps connection, the
lower limit of the adjust voltage command value becomes
approximately 1.2 V. The lower limit of 1.2 V of the adjust voltage
command value corresponds to a larger value than a no-load open
terminal voltage of the battery 2, for example, 12.8 V. Here, the
number of steps of the diode 1471 is not limited to two.
[0040] A diode-or circuit 1473 outputs a voltage by selecting a
larger one between the output voltage of the low-pass filter 144
and the lower limit of the adjust voltage command value 1.2 V. The
diode-or circuit 1473 outputs the adjust voltage lower limit 1.2 V
when the rotation speed of the rotor is low and the output voltage
of the frequency detecting device 143 is less than the lower limit
1.2 V of the adjust voltage command value. The diode-or circuit
1473 outputs the output voltage of the frequency detecting device
143 when the rotation speed of the rotor is high and the output
voltage of the frequency detecting device 143 is more than the
lower limit 1.2 V of the adjust voltage command value.
[0041] A Zener diode 1474 determines an upper limit of the adjust
voltage command value, and a breakdown voltage thereof is set to
the upper limit of the adjust voltage command value corresponding
to the adjust voltage 14.5 V, for example, 1.36 V.
[0042] The adjust voltage command value determined as described
above is applied to a positive input terminal of the comparator 148
through a signal line 1476.
[0043] FIG. 3 shows a relationship between the adjust voltage value
output by the adjust voltage generating device 147 and the rotation
speed of the alternator 1.
[0044] In the present embodiment, as shown in FIG. 3, a rotation
speed Nmin corresponding to a lower limit Vfmin (corresponding to
adjust voltage command value 1.2 V) of the adjust voltage is set to
a value higher than a generation start rotation speed (here, 1000
rpm) of the alternator 1, for example the rotation speed of the
generator at around 1200 rpm. A rotation speed Nmax corresponding
to an upper limit Vfmax (corresponding to adjust voltage command
value 1.36V) of the adjust voltage is set at 1.5 through 2 times of
the generation start rotation speed, for example, in the vicinity
of 1800 rpm.
[0045] A control operation of this apparatus will be explained with
reference to FIG. 4 being a timing chart. Ne denotes a rotation
speed of the alternator 1, Vp denotes a wave form of a one-phase AC
voltage, Vreg denotes an adjust voltage command value, and Vfv
denotes an output voltage, which is referred to also as DC voltage,
of the low-pass filer 144.
[0046] Since the rotor of the alternator 1 has 2 p ("p" denotes the
number of magnetic pole pairs) pieces of magnetic poles, when the
rotor rotates at N [rpm], the AC voltage having the fundamental
frequency of N.quadrature.p/60 [Hz] is induced in the armature coil
11 during generation. For example, when the number of the magnetic
poles is twelve, and the rotation speed of the rotor is 1500 rpm, a
fundamental frequency component of the induced AC voltage is 150
Hz. When the number of the magnetic poles is sixteen, the number of
the rotation speed of the rotor is 1800 rpm, the fundamental
frequency component of the induced AC voltage is 240 Hz.
[0047] Since an output terminal of the armature coil 11 is
connected to the battery 2 through the three phases full wave
rectifier 12, upper and lower limits of the induced AC voltage are
clamped at constant voltages. The waveform of the AC voltage is
formed in a rectangular wave shape having approximately 50% of duty
ratio. The upper limit thereof is, for example, 14.5 V
substantially equal to a terminal voltage of the battery. The lower
limit thereof is substantially 0 V.
[0048] When the rotation speed changes, frequency of the waveform
Vp of the AC voltage generated in the armature coil 11 changes
according to the change of the rotation speed as shown in FIG. 4.
Signal voltage Vfv is f/V converted by the frequency detecting
device 143 and low-pass extracted by the low-pass filter 144. The
adjust voltage generating device 147 converts the signal voltage
Vfv into the adjust voltage command value Vreg. The adjust voltage
command value Vreg is compared with the partial voltage of the
battery voltage by the comparator 148, and the power transistor 149
is switching controlled.
[0049] In the present embodiment, when the engine speed is reduced
by the current load, the adjust voltage command value Vreg is also
reduced with the reduction of the rotation speed. Even when the
duty ratio of the power transistor 149 is reduced by the reduction
of the adjust voltage Vreg, the field current is not immediately
reduced to 0, and the field current is continued to flow through
the fly wheel diode 145 until magnetic energy accumulated in the
field magnetic circuit is disappeared. A field magnetic flux is
continued to generate, and the armature coil 11 continues to
generate. Further, a recent high output alternator uses a field
circuit up to a magnetic saturation level. Thus, after that, even
when the field current is attenuated to a certain degree, an actual
field flux still stays in an almost un-attenuated state. Thus, an
electric power generation is highly effectively conducted. Here,
the rotation speed is reduced and the adjust voltage is also
reduced, so that the generated voltage is gradually reduced along
the above-described attenuation of the magnetic energy accumulated
in the field magnetic circuit. Thus, the battery 2 operates to
cancel a charging polarization thereof. However, since the
generated power is approximately maintained for the reason that the
field circuit is used normally in a high magnetic saturation field
as described above, the reduction of the generated voltage
increases the generated current that the generator outputs, and the
generated current satisfies an electric current amount required by
the electric load device 3. As a result, electric discharge from
the battery 2 to the electric load device 3 is excellently
restrained, so that the battery 2 does not perform a considerable
discharge.
[0050] When the adjust voltage is not reduced, the adjust voltage
Vreg is maintained at a constant voltage when the electric load is
applied and the engine rotation speed is reduced, regardless the
reduction of rotation speed. Thus, reduction of the generation
output due to reduction of the rotation speed, and reduction of the
battery voltage due to reduction of the generated voltage increases
the duty of the transistor 149. Thus, driving torque (load torque
viewed from engine) of the alternator 1 is increased, and the
engine rotation speed is further reduced. Further, the generator
rotation speed is further reduced, and the rotation speed is
reduced to a range in which the power generation capacity of the
generator is deficient with respect to the required load amount,
thereby introducing the considerable discharge of the battery
2.
[0051] Next, an increasing aspect of the rotation speed after
increasing for a while engine torque by an engine fuel injection
control system detecting the reduction of the engine rotation speed
will be explained.
[0052] When a reduction control of the adjust voltage (follow-up of
rotation speed) is executed, as described above, the discharge of
the battery 2 remains in a slight amount, so that an additional
generation by the generator is not necessitated to recover the
charge of the battery 2. Accordingly, the engine does not have to
perform a torque increase including a portion of an increase of the
drive torque corresponding to the additional generation. Moreover,
since the adjust voltage is increased in accordance with an
increase of the rotation speed, the battery charge for the recovery
of the charge polarization of the battery 2 and for restoring the
battery voltage to an original state is gently performed following
to an increase of the generation output corresponding to an
increase of the rotation speed, so that an overshoot of the
rotation speed is not generated.
[0053] Contrary to this, when the adjust voltage is not reduced,
discharge of the battery 2 is considerable so far, and the duty of
the transistor 147 is large. Thus, the load torque viewed from the
engine becomes large, an increase of the engine torque delays, and,
the increase of the engine torque after recovering the engine
torque becomes remarkably large comparing with the adjust voltage
control in the present embodiment. As a result, the rotation speed
is recovered, the battery charge is completed, the battery voltage
is recovered, and the driving torque of the alternator 1 is
decreased. Then, an increase of the engine rotation speed, that is,
the overshoot becomes large, and a hunting occurs due to a response
delay of the feedback control system of fuel injection. In the
prior art, even in a recovery aspect of the engine rotation speed,
the adjust voltage is made as a constant. Thus, in a bottom of the
engine rotation speed, that is, in an early stage of the recovery
of the engine rotation speed, above-described problem leads to
perform a large generation due to a large or small relationship
between not reduced adjust voltage and reduced battery voltage.
Therefore, the overshoot of the rotation speed after that (after
completing battery charge), and the hunting after that become
furthermore serious problems.
[0054] As a second advantage of a follow-up control of the rotation
speed to the adjust voltage in the present embodiment, as described
above, since a frequent charge and discharge of the battery 2 due
to the intermission of the electric load can be suppressed,
sufficient life span of the battery is attained.
[0055] Here, during an engine idling and battery charging, the
battery voltage is not reduced below a no-load open voltage (for
example, 12.8 V). That is, unless reducing the adjust voltage below
12.8 V, the battery is not brought into the considerable discharge
state. Accordingly, by providing the adjust voltage command value
(partial voltage of adjust voltage) with a lower limit, and setting
the corresponding rotation speed thereof higher than the generation
start rotation speed of the generator, a considerable discharge of
the battery 2 is easily prevented from occurring.
[0056] Further, when the adjust voltage is continued to be raised
with an increase of the rotation speed, the battery is excessively
charged, and not only the life span of the battery is shortened due
to rapid reduction of battery electrolyte, but also it is possible
to reach an excessive voltage considered so as to cause damage
appropriate operations of any vehicle equipment. In order to
prevent such a phenomenon, in the present embodiment, the adjust
voltage command value is provided with the upper limit, the
rotation speed corresponding to the upper limit is set 1.5 through
2 times of the generation start rotation speed of the generator.
That is, by executing the adjust voltage control of the present
embodiment only in the vicinity of the idling engine speed, and by
controlling the rotation speed at the upper limit of adjust voltage
during normally running, the problem described above is solved.
[0057] Here, an operation delay of the low-pass filter 144
connected to the rear stage of the frequency detecting means 143,
for example, in the CR low-pass filter, a CR time constant thereof
should be set small, and preferably desirable to be set less than
0.1 seconds.
[0058] A hunting restraining effect, in a case where the present
embodiment is applied to the alternator commercially available is
shown in FIG. 5, and a relationship between an output current and
the driving torque in various output voltages of the normal
alternator is shown in FIG. 6.
[0059] As in the present embodiment, even when the output voltage
is changed within the range of 1-1.5 V, power to be generated by
the alternator 1 is approximately constant. Strictly speaking, the
higher the voltage, the larger becomes output power, however,
within the range of 1-1.5 V and particularly within the range of
low rotation speed, increase and decrease of the output power is
negligible. That is, in a region of low rotation speed, since the
output power being a product of the output voltage and the output
current is approximately constant, the output current is increased
when the output voltage is reduced.
[0060] Particularly in a small type high output alternator in
recent years, an armature reaction is small in a low speed area.
Thus, a main magnetic flux is not led to be demagnetized, the
armature and the core of the field poles are operated in high
saturated states thereof. Then, the field flux is considered
approximately constant with a slight decrease of any amount of
exciting current, and the output power thereof is not reduced.
[0061] In this case, since the output voltage is being reduced in
accordance with the reduction of the rotation speed, the torque
sudden change points are moved in order of N4, N3, N2, and N1.
[0062] For example, when the alternator is operated at a value of
N5 of the rotation speed slightly higher than the value N4 of the
rotation speed, and at the operational point T4, if the control of
the present embodiment is applied, the output voltage is reduced
following to the reduction of the rotation speed, and the
operational points are moved in order of T4, T3, T2, T1, and
T0.
[0063] That is, in the prior art, the inflection point of the
torque is accepted at the rotation speed N4. However, in the
present embodiment, that can be reduced to NO of the rotation
speed. That is, even when the electric load is applied and the
engine rotation speed is suddenly reduced, the torque inflection
point of the alternator 1 is positioned outside a drop range of the
engine rotation speed.
[0064] Even when the engine rotation speed is reduced, the driving
torque of the alternator does not exceed the torque inflection
point (point at which driving torque of alternator viewed from
engine side changes from decreasing tendency to increasing
tendency). This means that the generation duty ratio of the
alternator does not reach 100%, and that the generation capacity of
the alternator is regarded as apparently improved. In the control
of the present embodiment, a deviation between the battery voltage
and the target voltage (adjusting voltage) thereof is invariably
made small, so that even when the rotation speed is reduced, the
discharge of the battery is suppressed. As a result, when the
engine control system is entered in a recovering process of the
rotation speed, necessity to charge the battery is reduced. Thus,
the torque fluctuation of the alternator is reduced, and an idle
hunting is converged in an early stage.
[0065] When the adjust voltage is continuously changed in
accordance with a change of the rotation speed, the fluctuation of
the operational torque described above is more smoothly performed.
That is, the discharge of the battery 2 is inhibited even at a low
speed side, and re-charge after that is suppressed.
[0066] (Modifications)
[0067] A characteristic of an adjust voltage in the modification is
shown in FIG. 7.
[0068] In the modification, a control of the adjust voltage is
changed like a multi-stages stair from a lower limit to an upper
limit within a predetermined frequency range. By changing like
this, digital processing of detected rotation speed signals becomes
easy.
[0069] Note, a terminology referred to as "DC voltage" used in the
present specification includes a low-pass AC component.
* * * * *