U.S. patent application number 09/803914 was filed with the patent office on 2001-09-27 for electric energy charging control apparatus and method for hybrid vehicle.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Suzuki, Naoto.
Application Number | 20010024104 09/803914 |
Document ID | / |
Family ID | 18599509 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024104 |
Kind Code |
A1 |
Suzuki, Naoto |
September 27, 2001 |
Electric energy charging control apparatus and method for hybrid
vehicle
Abstract
A controller predicts a requested state of charge/discharge
corresponding to a future run of a hybrid vehicle. If it is
predicted that the hybrid vehicle will be stopped and restarted, or
will be greatly accelerated and therefore that a request for a
great discharge will be outputted in the future, the controller
increases a target SOC of an HV battery to increase the value to
which the charge of the HV battery will be converged in preparation
for the great discharge. If it is predicted that a great
regenerative electric power will be generated by a vehicle
deceleration and therefore that a request for charging will be
outputted, the target SOC is reduced, and the amount of charge in
the HV battery is reduced, so that the regenerative power generated
can be efficiency recovered.
Inventors: |
Suzuki, Naoto;
(Fujinomiya-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
277 S. WASHINGTON STREET, SUITE 500
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
|
Family ID: |
18599509 |
Appl. No.: |
09/803914 |
Filed: |
March 13, 2001 |
Current U.S.
Class: |
320/104 ;
903/903 |
Current CPC
Class: |
B60W 2510/244 20130101;
Y02T 10/70 20130101; B60L 15/2045 20130101; B60K 6/48 20130101;
B60W 2710/244 20130101; Y02T 90/16 20130101; B60W 20/10 20130101;
Y10S 903/903 20130101; B60W 2555/20 20200201; B60W 10/08 20130101;
Y02T 10/62 20130101; Y02T 10/72 20130101; Y02T 10/64 20130101; B60W
10/26 20130101; B60L 58/12 20190201; B60W 50/0097 20130101; B60L
50/16 20190201; B60W 2520/10 20130101; B60L 2240/662 20130101; B60W
20/00 20130101; B60W 2530/00 20130101; B60L 50/61 20190201; B60W
10/24 20130101; B60W 2510/305 20130101; Y02T 10/7072 20130101 |
Class at
Publication: |
320/104 |
International
Class: |
H02J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2000 |
JP |
2000-082748 |
Claims
What is claimed is:
1. An electric energy charging control apparatus of a hybrid
vehicle having an internal combustion engine, a motor-generator
capable of assisting running of the vehicle and an electric energy
storage device connected to the motor-generator, the control
apparatus comprising a controller that: predicts a future state of
a charge/discharge of the electric energy storage device; and
changes a target value of charge of the electric energy storage
device based on a result of the prediction regarding the future
state of the charge/discharge of the electric energy storage
device.
2. The electric energy charging control apparatus according to
claim 1, wherein the controller predicts the future state based on
a state of the run of the vehicle, and changes the target value by:
increasing the target value of charge when the state of the run of
the vehicle is a state in which at least a predetermined amount of
the charge is predicted to be discharged from the electric energy
storage device, and by reducing the target value of charge when the
state of the run of the vehicle is a state in which at least a
predetermined amount of the charge is predicted to be charged into
the electric energy storage device.
3. The electric energy charging control apparatus according to
claim 1, wherein the controller changes the target value of charge
of the electric energy storage device in accordance with a vehicle
ambient temperature.
4. The electric energy charging control apparatus according to
claim 2, wherein the state of the run of the vehicle is a vehicle
speed of the vehicle.
5. The electric energy charging control apparatus according to
claim 4, wherein if the vehicle speed of the vehicle is a low
vehicle speed for a predetermined time, the controller increases
the target value of charge of the electric energy storage device to
secure an amount of charge at least equal to an amount of charge
that will be consumed by the motor-generator in anticipation of the
vehicle being stopped or greatly accelerated.
6. The electric energy charging control apparatus according to
claim 4, wherein if the vehicle speed of the vehicle speed is a
high vehicle speed for a predetermined time, the controller
decreases the target value of charge of the electric energy storage
device to increase a region for recovery of a regenerative energy
that is to be obtained through the motor-generator in anticipation
of a future state of the vehicle being decelerated.
7. The electric energy charging control apparatus according to
claim 6, wherein: a quantity of charge of the electric energy
storage device corresponding to the decrease in the target value of
charge is used by the motor-generator to assist in driving the
vehicle, thereby reducing the output of the internal combustion
engine and improving fuel economy.
8. The electric energy charging control apparatus according to
claim 3, wherein if the vehicle ambient temperature of the vehicle
is lower than a predetermined temperature, the controller increases
the target value of charge of the electric energy storage device to
secure an amount of charge at least equal to an amount of charge
that will be consumed by the motor-generator in anticipation of a
low charging/discharging efficiency.
9. The electric energy charging control apparatus according to
claim 3, wherein if the vehicle ambient temperature of the vehicle
is at least equal to a predetermined temperature, the controller
only slightly increases the target value of charge of the electric
energy storage device to secure an amount of charge at least equal
to an amount of charge that will be consumed by the motor-generator
in anticipation of a normal start or acceleration.
10. A electric energy charging control method for a hybrid vehicle
including an internal combustion engine, a motor-generator capable
of assisting a run of the vehicle, and a electric energy storage
device connected to the motor-generator, the method comprising:
predicting a future state of charge/discharge of the electric
energy storage device; and changing a target value of charge of the
electric energy storage device based on a result of the prediction
regarding the future state of the charge/discharge of the electric
energy storage device.
11. The electric energy charging control method according to claim
10, wherein the future state of charge/discharge of the electric
energy storage device is predicted based on a state of the run of
the vehicle, and wherein: the target value of charge is increased
if, from the state of the run of the vehicle, at least a
predetermined amount of the charge is predicted to be discharged
from the electric energy storage device at a future time, and the
target value of charge is reduced if, from the state of the run of
the vehicle, at least a predetermined amount of the charge is
predicted to be charged into the electric energy storage device at
the future time.
12. The electric energy charging control method according to claim
10, wherein the target value of charge of the electric energy
storage device is changed in accordance with a vehicle ambient
temperature.
13. The electric energy control method according to claim 11,
wherein the state of the run of the vehicle is a vehicle speed of
the vehicle.
14. The electric energy charging control method according to claim
13, wherein: if the vehicle speed of the vehicle is a low vehicle
speed for a predetermined time, the target value of charge of the
electric energy storage device is increased to secure an amount of
charge at least equal to an amount of charge that will be consumed
by the motor-generator in anticipation of the vehicle being stopped
or greatly accelerated.
15. The electric energy charging control method according to claim
13, wherein: if the vehicle speed of the vehicle speed is a high
vehicle speed for a predetermined time, the target value of charge
of the electric energy storage device is decreased to increase a
region for recovery of a regenerative energy that is to be obtained
through the motor-generator in anticipation of a future state of
the vehicle being decelerated.
16. The electric energy charging control method according to claim
15, wherein: a quantity of charge of the electric energy storage
device corresponding to the decrease in the target value of charge
is used by the motor-generator to assist in driving the vehicle
thereby reducing the output of the internal combustion engine and
improving fuel economy.
17. The electric energy charging control method according to claim
12, wherein if the vehicle ambient temperature of the vehicle is
lower than a predetermined temperature, the target value of charge
of the electric energy storage device is increased to secure an
amount of charge at least equal to an amount of charge that will be
consumed by the motor-generator in anticipation of a low
charging/discharging efficiency.
18. The electric energy charging control method according to claim
12, wherein: if the vehicle ambient temperature of the vehicle is
at least equal to a predetermined temperature, the target value of
charge of the electric energy storage device is only slightly
increased to secure an amount of charge at least equal to an amount
of charge that will be consumed by the motor-generator in
anticipation of a normal start or acceleration.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2000-082748 filed on Mar. 23, 2000 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to electric energy charging control
apparatus and method for a hybrid vehicle. More specifically, the
invention relates to electric energy charging control apparatus and
method for hybrid vehicle, that achieve efficient utilization of an
electric energy storage device while allowing a size reduction of
the electric energy storage device in a hybrid vehicle that needs a
large amount of electric energy output in order to assist the
running of the vehicle through the use of a motor-generator.
[0004] 2. Description of the Related Art
[0005] Vehicles equipped with hybrid vehicle (HV) systems that
achieve great advantages in environmental protection and fuel
economy improvement (hereinafter, referred to as "hybrid vehicles
(HV)") are being developed and commercialized. An HV system is a
power train that uses a combination of two kinds of drive power
sources, for example, an internal combustion engine (a gasoline
engine, a diesel engine, etc.) and an electric motor. By
selectively using the engine and the electric motor in accordance
with the driving condition, the system makes full use of the
advantages of the two drive power sources, and supplements
disadvantageous aspects of the two drive power sources with each
other, so as to achieve smooth and highly responsive power
performance. That is, by operating one of the engine and the
electric motor alone or both of them in concert, the system is able
to improve fuel economy and considerably reduce exhaust emissions.
For example, during a low-load region where the engine efficiency
is low (in particular, at the time of a vehicle start or a very low
vehicle speed), the engine is not started, but the electric motor
alone is operated to drive the vehicle. When the vehicle enters a
speed region where the engine efficiency is high, the engine is
started and the electric motor is stopped. When an increased output
is needed, for example, during acceleration or the like, the engine
and the electric motor are simultaneously operated to perform
torque assist using the electric motor so that a desired output can
be obtained.
[0006] When the electric motor is used in this manner, electric
power is supplied from a battery installed in the vehicle.
Therefore, the hybrid vehicle needs to be equipped with a
large-capacity battery. In order to realize good use of the
electric motor as described above, the state of charge (SOC) of the
battery must always be controlled.
[0007] A typical hybrid vehicle is equipped with a motor-generator
(MG) that performs an electric motor function and a power
generating function. The MG is controlled so as to generate
electric power so that the amount of charge in the battery
converges to a target value of charge of the battery (target SOC).
For example, Japanese Patent Application Laid-Open No. HEI
11-299004 discloses a control method for maintaining a targeted SOC
by adjusting the engine output in accordance with the SOC.
[0008] Normally, the target SOC of a hybrid vehicle is set to a
fixed value (e.g., an amount of charge being 60% of the full
amount) with such a good margin between an upper limit and a lower
limit that a discharge request (an electric motor drive request)
and a charge request (a request for power charging through
regeneration) can be accepted.
[0009] However, with regard to the hybrid vehicles, there are
demands for reductions in vehicle weight, increases in compartment
space, reductions in vehicle cost, etc. Therefore, battery size
reductions are needed. If a battery is reduced in size, the battery
capacity naturally reduces. In that case, therefore, a problem
arises when the battery is to be charged or discharged. That is,
the amount of charge or discharge allowed with reference to the
target SOC reduces. As a result, it becomes impossible to discharge
an amount that is needed at the time of a vehicle start or
acceleration. A problem also arises at the time of deceleration.
That is, only a small amount of energy can be charged into the
battery although a large amount of regenerative electric power is
generated. Thus, the amount of electric energy generated cannot be
sufficiently utilized, and efficient utilization of energy
(battery) cannot be realized.
[0010] Furthermore, the chemical reactions that occur inside
batteries become slow when the battery ambient temperature
decreases. Therefore, at low temperatures, the charging/discharging
efficiency decreases, and sufficient charging/discharging becomes
impossible even when the state of charge has converged to a target
SOC. Therefore, according to the conventional art, it is inevitable
to provide large-capacity (large-size) batteries in preparation for
low ambient temperatures. Thus, the conventional art cannot meet
the demand for a battery size reduction.
SUMMARY OF THE INVENTION
[0011] Accordingly, it is an object of the invention to provide an
electric energy charging control apparatus of a hybrid vehicle that
is capable of performing the requested charging/discharging at a
high efficiency while allowing a size reduction of an electric
energy storage device.
[0012] In accordance with a first aspect of the invention, an
electric energy charging control apparatus of a hybrid vehicle
includes an internal combustion engine, a motor-generator capable
of assisting a run of the vehicle, an electric energy storage
device connected to the motor-generator, controller that predicts a
future state of charge/discharge of the electric energy storage
device and changes a target value of charge of the electric energy
storage device based on a result of prediction regarding
charge/discharge of the electric energy storage device.
[0013] According to this construction, if it is predicted that the
electric energy storage device will be discharged in the future,
the target amount of charge of the electric energy storage device
is changed to an increased value to increase the amount of charge
beforehand, so that when the discharging occurs, an increased
amount of discharge from the electric energy storage device can be
provided. Conversely, if it is predicted that the electric energy
storage device will be charged in the future, the target amount of
charge of the electric energy storage device can be changed to a
reduced value to reduce the amount of charge beforehand, so that
when the charging occurs, an increased amount of charge into the
electric energy storage device can be achieved. Therefore, a
substantial electric energy charging/discharging range can be
expanded. As a result, it becomes possible to efficiently perform
charging/discharging as requested while allowing a size reduction
of the electric energy storage device.
[0014] In the above-described aspect, the controller may predict
the future state of the charge/discharge of the electric energy
storage device based on a state of the run of the vehicle, and may
increase the target value of charge when the state of the run of
the vehicle is a state where it is predicted that at least a
predetermined amount is discharged from the electric energy storage
device, and the target value changing means may reduce the target
value of charge when the state of the run of the vehicle is a state
where it is predicted that at least a predetermined amount will be
charged into the electric energy storage device.
[0015] The controller performs prediction regarding the
charge/discharge of the electric energy storage device based on,
for example, vehicle speed information. For example, if a low
vehicle speed continues for a predetermined time, it is predicted
that the vehicle will be stopped or greatly accelerated in the
future. In association with a stop or a great acceleration, a large
amount of electric energy will be consumed by the electric motor
function of the motor-generator. Therefore, the target amount of
charge of the electric energy storage device is increased to secure
a sufficient amount of charge beforehand. Conversely, if a high
vehicle speed continues for a predetermined time, it is predicted
that the vehicle will be decelerated in the future. At the time of
a deceleration, a great amount of regenerative energy will be
obtained by the power generating function of the motor-generator.
Therefore, the target amount of charge is reduced to increase the
region for recovery of regenerative energy beforehand, so that
regenerative energy will be sufficiently recovered. This
construction makes it possible to efficiently perform
charging/discharging as requested while allowing a size reduction
of the electric energy storage device.
[0016] In the above-described aspect, the controller may change the
target value of charge of the electric energy storage device in
accordance with a vehicle ambient temperature.
[0017] According to this construction, if the vehicle ambient
temperature is low, for example, below the freezing point, the
target value of charge is increased so as to compensate for a
reduction in the charging/discharging efficiency of the electric
energy storage device caused by low temperature. Therefore, it is
possible to efficiently perform charging/discharging as requested
while allowing a size reduction of the electric energy storage
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of preferred embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements and wherein:
[0019] FIG. 1 is a conceptual diagram of a construction of a
vehicle having a battery charging control apparatus in accordance
with an embodiment of the invention;
[0020] FIG. 2 is a functional block diagram illustrating a target
SOC changing procedure performed by a control unit of the vehicle
having the battery charging control apparatus in accordance with
the embodiment of the invention;
[0021] FIG. 3 is a diagram illustrating a concept of calculation of
a requested amount of power generation with respect to the SOC of a
battery performed by the battery charging control apparatus in
accordance with the embodiment of the invention;
[0022] FIG. 4 is a flowchart illustrating the target SOC changing
procedure performed by the battery charging control apparatus in
accordance with the embodiment of the invention;
[0023] FIG. 5 is a diagram indicating changes in the SOC of an HV
battery, changes in the vehicle speed of an hybrid vehicle, and
changes in the target SOC that occur at the time of the control by
the battery charging control apparatus in accordance with the
embodiment of the invention; and
[0024] FIG. 6 is a flowchart illustrating a target SOC changing
procedure performed by the battery charging control apparatus in
accordance with the embodiment of the invention, taking into
consideration the external air temperature.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0025] A preferred embodiment of the invention (hereinafter,
referred to as "embodiment") will be described hereinafter with
reference to the accompanying drawings.
[0026] FIG. 1 shows a conceptual diagram of a construction of a
hybrid vehicle (HV) 10 in accordance with the embodiment of the
invention. The hybrid vehicle 10 includes, as drive power sources,
an internal combustion engine (hereinafter, simply referred to as
"engine"), for example, a gasoline engine, a diesel engine, etc.,
and a motor-generator (MG) 14. In FIG. 1, the MG 14 is illustrated
as an electric motor 14A and a generator 14B for the sake of
convenience in illustration. However, in accordance with the
running state of the hybrid vehicle 10, the electric motor 14A can
function as a generator, and the generator 14B can function as an
electric motor.
[0027] The hybrid vehicle 10 further includes: a speed reducer 18
for transmitting power generated by the engine 12 or the MG 14
toward a wheel side 16 and transmitting the drive power from the
wheel side 16 to the engine 12 or the MG 14; a power splitter
mechanism (e.g., a planetary gear in FIG. 1) 20 for distributing
the power generated by the engine 12 to two paths, that is, to the
wheel side 16 and the generator 14B; an HV battery 22 as an
electric energy storage device for storing electric power for
driving the MG 14; an inverter 24 for performing current control
while performing conversion between the direct current related to
the HV battery 22 and the alternating current related to the
electric motor 14A and the generator 14B; a battery electronic
control unit (hereinafter, referred to as "battery ECU") 26 for
managing and controlling the state of charge/discharge of the HV
battery 22; an engine ECU 28 for controlling the operation state of
the engine 12; an MGECU 30 for controlling the MG 14, the battery
ECU 26, the inverter 24, etc., in accordance with the state of the
hybrid vehicle 10; an HVECU 32 for controlling the entire HV system
so that the hybrid vehicle 10 can run at a maximum efficiency by
managing and controlling the battery ECU 26, the engine ECU 28, the
MGECU 30, etc. in an interrelated manner; etc. Although in FIG. 1,
the ECUs are separate units, two or more of the ECUs may be
integrated into a single ECU.
[0028] In the hybrid vehicle 10 equipped with the HV system as
shown in FIG. 1, the electric motor 14A of the MG 14 alone is used
to drive the hybrid vehicle 10 when the efficiency of the engine 12
is low, for example, at the time of a vehicle start, a low-speed
travel, etc. During a normal travel, for example, the power from
the engine 12 is divided into the two paths by the power splitter
mechanism 20, so as to directly drive the wheel side 16 on one hand
and drive the generator 14B for electric power generation on the
other hand. The electric power thus generated is used to drive the
electric motor 14A so as to assist the driving of the wheel side
16. During a high-speed travel, electric power from the HV battery
22 is supplied to the electric motor 14A to increase the output of
the electric motor 14A, thereby adding to the drive power for the
wheel side 16. During a deceleration, the electric motor 14A,
driven by the wheel side 16, functions as a generator to perform
regenerative power generation. The thus-recovered power is stored
into the HV battery 22. When the amount of charge in the HV battery
22 decreases so that the charging of the HV battery 22 is needed,
the output of the engine 12 is increased to increase the power
generated by the generator 14B in order to increase the amount of
charge in the HV battery 22. Even during a low-speed travel, a
control of increasing the amount of driving output of the engine 12
is performed if necessary, for example, when the charging of the HV
battery 22 is needed, or when an accessory appliance, such as an
air-conditioner or the like, is driven, or when the temperature of
cooling water of the engine 12 is to be raised to a predetermined
temperature.
[0029] A feature of this embodiment is that even if the HV battery
22 is reduced in size and therefore is reduced in capacity, the
efficient charging/discharging of the HV battery 22 is performed by
predicting a future charge/discharge state of the HV battery 22 and
appropriately changing a target state of charge (target SOC) of the
HV battery 22.
[0030] FIG. 2 is a block diagram illustrating internal
constructions of the ECUs shown in FIG. 1 separately for functions,
to help describe the changing of the target SOC of the HV battery
22 in relation with the ECUs.
[0031] Normally, the HVECU 32, while controlling the driving of the
hybrid vehicle 10, generally manages the output of the engine 12
and the driven state of the MG 14 so that the SOC of the HV battery
22 converges to the target SOC. The target SOC is set to a default
value of 60% or so in order to allow both the charging and the
discharging to be performed to some extents.
[0032] The overall control of the hybrid vehicle 10 will next be
described. Firstly, an accelerator operation recognizing portion 34
included in the HVECU 32 recognizes an amount of depression of an
accelerator caused by a driving person through the use of a sensor
36a disposed on an accelerator pedal 36. A vehicle speed
recognizing portion 38 recognizes a present vehicle speed of the
hybrid vehicle 10 based on information from a vehicle speed sensor
40 and the like. An output shaft torque calculating portion 42
calculates an output shaft torque needed to achieve a traveling
state requested by the driving person, based on the amount of
accelerator operation and the vehicle speed. A needed vehicle power
calculating portion 44 calculates an engine power needed to achieve
the traveling state requested by the driving person. An accessory
requested amount recognizing portion 46 calculates an energy needed
to operate an accessory 48, such as an air-conditioner or the like,
based on the operation state of the accessory 48.
[0033] An SOC recognizing portion 50 included in the battery ECU 26
checks the state of charge of the HV battery 22. A target SOC is
set in the battery ECU 26 in order to maintain an optimal SOC of
the HV battery 22. Normally, a requested power generation amount
calculating portion 52 calculates a requested amount of power
generation that can be generated by the generator 14B such that the
SOC converges to the target SOC (e.g., 60%). For example, if the
present SOC of the HV battery 22 recognized by the SOC recognizing
portion 50 is 50% when the target SOC has been set to 60%, the
power generation of 4 kW is requested as indicated in FIG. 3. If
the present SOC of the HV battery 22 is 70%, the power generation
of -4 kW, that is, the discharge of 4 kW, is requested.
[0034] As mentioned above, there are cases where depending on a
further travel of the hybrid vehicle 10, the discharging of a great
amount of power is requested, or the charging of a great amount is
requested in response to generation of a great amount of
regenerative power. However, if the HV battery 22 is reduced in
size, the amount of charge or discharge allowed with reference to
the target SOC reduces, so that sufficient charging/discharging may
become impossible. Therefore, a charge/discharge predicting portion
(charge/discharge predicting means) 54 included in the HVECU 32
predicts what manner of running the hybrid vehicle 10 will undergo
in the future, based on, for example, information from the vehicle
speed recognizing portion 38. Based on a result of the prediction,
a target SOC changing portion (target value changing means) 56
included in the HVECU 32 changes the target SOC from the default
value of 60%. For example, if a low vehicle speed continues for at
least a predetermined time, it is predicted that the hybrid vehicle
10 will be stopped, or will be greatly accelerated in the future.
If the hybrid vehicle 10 is stopped, the next action performed is a
start. As mentioned above, at the time of starting, the engine
revolution speed needs to be quickly raised. Therefore, it is
predicted that discharge from the HV battery 22 will be performed.
In particular, if the engine 12 is a diesel engine having a
relatively great friction, it is predicted that a further increased
amount of discharge will be caused. Furthermore, when the hybrid
vehicle 10 is greatly accelerated, it is desirable that the torque
assist by the electric motor 14A be performed. Therefore, great
discharge from the HV battery 22 is predicted. Thus, when the
hybrid vehicle 10 is running at a low vehicle speed, the next
traveling operation predicted involves the consumption of a great
amount of electric energy by the electric motor 14A. Therefore, it
is necessary to have an increased amount of electric power ready.
Hence, the target SOC is increased to secure a sufficient amount of
charge.
[0035] Conversely, if a high vehicle speed continues for at least a
predetermined time, it is predicted that the hybrid vehicle 10 will
be decelerated in the future. Since a great amount of regenerative
energy will be obtained through the generator 14B during
acceleration, the target SOC is reduced to increase the free
capacity of the HV battery 22 so that the regenerative energy will
be recovered without wastage. In order to increase the free
capacity of the HV battery 22, it is necessary to discharge the HV
battery 22 by using the electric motor 14A. By driving the electric
motor 14A based on the discharge, the drive power for the hybrid
vehicle 10 can be increased, so that the output of the engine 12
can be correspondingly reduced and the fuel economy can be
improved.
[0036] An example of the procedure of changing the target SOC will
be described with reference to the flowchart of FIG. 4. First, the
target SOC changing portion 56 sets the target SOC to the default
value of 60% (S100). Subsequently, the charge/discharge predicting
portion 54 acquires vehicle speed information from the vehicle
speed recognizing portion 38, and determines whether a high vehicle
speed has continued for a predetermined time (S101). For example,
if the hybrid vehicle 10 has been traveling at a high vehicle speed
of at least 80 km/h (an average vehicle speed of 80 km/h) for at
least 5 minutes, the charge/discharge predicting portion 54
predicts that the hybrid vehicle 10 will be decelerated at some
future time. As described above, when the hybrid vehicle 10 is
decelerated, the generator 14B is driven by a drive power obtained
from the wheel side 16, thereby performing regenerative power
generation. In this case, the regenerated electric power increases
with increases in deceleration. Therefore, in order to recover as
much regenerative power as possible, a region for charging
regenerative power is made ready in the HV battery 22 beforehand.
That is, in order to reduce the present SOC of the HV battery 22,
the target SOC is changed from the default value of 60% to, for
example, 50% (S102).
[0037] Conversely, if the charge/discharge predicting portion 54
determines in S101 that the high vehicle speed has not continued
for the predetermined time, the charge/discharge predicting portion
54 then determines whether a low vehicle speed has continued for a
predetermined time (S103). For example, if the hybrid vehicle 10
has been traveling at a low vehicle speed of at most 20 km/h (an
average vehicle speed of 20 km/h) for at least 5 minutes, the
charge/discharge predicting portion 54 predicts that the hybrid
vehicle 10 will be stopped or greatly accelerated at some future
time. As described above, after the hybrid vehicle 10 is stopped,
restarting will be performed, so that the driving of the electric
motor 14A will be needed and a large amount of discharge from the
HV battery 22 will be caused. In the case of great acceleration,
too, the driving of the electric motor 14A is needed, so that a
large amount of discharge from the HV battery 22 will be caused. In
order to previously secure the power discharged in such a case, the
target SOC of the HV battery 22 is changed from the default value
of 60% to, for example, 70% (S104) to increase the present SOC. If
it is determined in S103 that the low vehicle speed has not
continued for the predetermined time, the target SOC of 60% is
maintained.
[0038] After the target SOC changing portion 56 supplies the
thus-determined target SOC to the requested power generation amount
calculating portion 52, the requested power generation amount
calculating portion 52 determines a requested amount of power
generation by comparing the target SOC with the present SOC of the
HV battery 22 recognized by the SOC recognizing portion 50. That
is, if the present SOC is 50% whereas the target SOC has been
changed to 70%, power generation of 8 kW is requested as indicated
by a broken line in FIG. 3. If the present SOC is 60% whereas the
target SOC has been changed to 50%, power generation of -4 kW, that
is, discharge of 4 kW, is requested as indicated by a one-dot chain
line in FIG. 3. In short, it is determined how much the output of
the engine 12 should be increased or reduced in order for the
generator 14B to perform the power generation needed.
[0039] After that, an engine output determining portion 58 included
in the HVECU 32 determines an engine output, that is, a total of an
engine power needed to achieve a driving person-requested traveling
state that is calculated by the needed vehicle power calculating
portion 44, an engine power needed to obtain an amount of energy
needed to operate the accessory 48 which is calculated by the
accessory requested amount recognizing portion 46, and an engine
power needed to obtain an amount of generated power needed to
converge the SOC of the HV battery 22 to the target SOC determined
through calculation by the requested power generation amount
calculating portion 52.
[0040] After an engine output is determined, the HVECU 32 operates
as described below so that the hybrid vehicle 10 will run at a
highest efficiency. That is, an engine revolution determining
portion 62 included in the engine ECU 28 determines an engine
revolution speed, and a fuel injection amount/ignition timing
determining portion 64 determines an amount of fuel injected and an
ignition timing, thereby controlling the running of the hybrid
vehicle 10.
[0041] FIG. 5 indicates changes in the SOC of the HV battery 22
(thick solid line), changes in the vehicle speed of the hybrid
vehicle 10 (thin solid line), and changes in the target SOC (broken
line). The target SOC has been increased to 70% as a result of a
stop of the hybrid vehicle 10. Simultaneously with a starting
operation, the SOC of the HV battery 22 considerably decreases.
However, a sufficient and smooth start of the hybrid vehicle 10 is
realized since the amount of charge of the HV battery 22 has been
increased beforehand by increasing the target SOC. Referring to
FIG. 5, it is recognized that the average vehicle speed is 20 km/h,
and the target SOC is maintained at 70% for a while, so that the
SOC of the HV battery 22 is converged to 70% in preparation for a
predicted future restart or great acceleration. After that,
acceleration is performed, and it is recognized that the average
vehicle speed is 80 km/h. Then, the target SOC is changed to 50%,
so that the SOC of the HV battery 22 is converged to 50% in
preparation for the recovery of regenerative power caused by a
predicted future deceleration.
[0042] Thus, even if the HV battery 22 is reduced in capacity
(reduced in size), it is possible to perform smooth start or
acceleration by predicting a future charge/discharge situation of
the HV battery 22 of the hybrid vehicle 10 and securing a
sufficient amount of charge prior to a request for a large amount
of discharge. Furthermore, before a great regenerative power is
obtained and a great charging request is outputted, a sufficient
region for charging is secured such that the regenerative power can
be recovered without wastage, and the electric motor 14A is
actively used in order to secure a region for charging. As a
result, the output of the engine 12 can be reduced, so that the
fuel economy can be improved and the HV battery 22 can be used at a
high efficiency as a whole.
[0043] FIG. 6 shows a flowchart illustrating a procedure of
changing the target SOC taking into consideration that the
charging/discharging efficiency of the HV battery 22 decreases
depending on the vehicle ambient temperature.
[0044] First, as in the flowchart of FIG. 4, the target SOC
changing portion 56 sets the target SOC to the default value of 60%
(S200). Subsequently, the charge/discharge predicting portion 54
acquires vehicle speed information from the vehicle speed
recognizing portion 38, and determines whether a high vehicle speed
has continued for a predetermined time (S201). For example, if the
hybrid vehicle 10 has been traveling at a high vehicle speed of at
least 80 km/h (an average vehicle speed of 80 km/h) for at least 5
minutes, the charge/discharge predicting portion 54 predicts that
the hybrid vehicle 10 will be decelerated and regenerative power
generation will be performed at some future time, and therefore
predicts that an allowance for charging will be needed. As
described above, when the hybrid vehicle 10 is decelerated, the
generator 14B is driven by drive power obtained from the wheel side
16, thereby performing regenerative power generation. In this case,
the power regenerated increases with increases in deceleration.
Therefore, in order to recover as much regenerative power as
possible, a region for charging regenerative power is prepared in
the HV battery 22 beforehand. That is, in order to reduce the
present SOC of the HV battery 22, the target SOC changing portion
56 changes the target SOC from the default value of 60% to, for
example, 50% (S202).
[0045] Conversely, if the charge/discharge predicting portion 54
determines in S201 that the high vehicle speed has not continued
for the predetermined time, the charge/discharge predicting portion
54 determines whether a low vehicle speed has continued for a
predetermined time (S203). For example, if the engine 12 has been
traveling at a low vehicle speed of at most 20 km/h (an average
vehicle speed of 20 km/h) for at least 5 minutes, the
charge/discharge predicting portion 54 predicts that a great amount
of discharge will be requested in the future. In this case, the
charge/discharge predicting portion 54 also determines whether the
ambient temperature of the hybrid vehicle 10 is lower than a
predetermined temperature, for example, 0.degree. C., based on
information from an external temperature sensor or the like (S204).
If the external air temperature is lower than the predetermined
temperature, the chemical reactions within the HV battery 22 become
slow and the charging/discharging efficiency becomes low, so that
the charge/discharge predicting portion 54 outputs to the target
SOC changing portion 56 a command to increase the target SOC to,
for example, 70%, in order to increase the amount of charge in the
HV battery 22 beforehand (S205), in preparation for a large
discharge request under a situation of a low charging/discharging
efficiency (in particular, a start of the electric motor 14A below
a freezing point or the like). As a result, when the hybrid vehicle
10 is started by the electric motor 14A, sufficient discharging
from the HV battery 22 can be achieved and the hybrid vehicle 10
can be smoothly started, even if the charging/discharging
efficiency of the HV battery 22 has fallen due to low
temperature.
[0046] If the charge/discharge predicting portion 54 determines in
S204 that the external air temperature is not below the
predetermined temperature, that is, if it can be determined that
the external air temperature does not adversely affect the chemical
reactions in the HV battery 22, the charge/discharge predicting
portion 54 outputs to the target SOC changing portion 56 a command
to change the target SOC to a slightly increased value, for
example, 65%, in preparation for a large amount of discharge at the
time of a normal start or acceleration (S206). If it is determined
in S203 that the low vehicle speed has not continued for the
predetermined time, it is considered that a request for extreme
charging/discharging of the HV battery 22 will not be made, and the
target SOC is maintained at 60%.
[0047] Thus, by predicting how much of charging/discharging is
needed for the next running of the hybrid vehicle 10 taking into
consideration the charging/discharging efficiency of the HV battery
22 in addition to the present running state of the hybrid vehicle
10, it becomes possible to secure a sufficient amount of
charge/discharge even if the HV battery 22 is reduced in size so
that the charging/discharging range with reference to the target
SOC is narrow. Thus, the HV battery 22 can be efficiently used.
[0048] In the embodiment, the default value of the target SOC is
set to 60%, and the increased values thereof are set to 65% and
70%, and the reduced value thereof is set to 50%. However, these
set values are arbitrary. It is preferable to select suitable set
values taking into consideration the capability of the HV battery
22, the performance of the hybrid vehicle 10, the environment of
use, etc. Furthermore, the conditions for changing the target SOC,
such as the predetermined speed (average speed), the duration of
continuation of the speed, the external air temperature, etc., are
also arbitrary. That is, it is preferable to select suitable
conditions.
[0049] In the above embodiment, the HV battery 22 is used as an
electric energy storage device. However, the electric energy
storage device of the invention is not limited only to a battery. A
condenser may also be used as an electric energy storage device of
the invention.
[0050] In the illustrated embodiment, the controller (the HVECU 32)
is implemented as a programmed general purpose computer. It will be
appreciated by those skilled in the art that the controller can be
implemented using a single special purpose integrated circuit
(e.g., ASIC) having a main or central processor section for
overall, system-level control, and separate sections dedicated to
performing various different specific computations, functions and
other processes under control of the central processor section. The
controller can be a plurality of separate dedicated or programmable
integrated or other electronic circuits or devices (e.g., hardwired
electronic or logic circuits such as discrete element circuits, or
programmable logic devices such as PLDs, PLAs, PALs or the like).
The controller can be implemented using a suitably programmed
general purpose computer, e.g., a microprocessor, microcontroller
or other processor device (CPU or MPU), either alone or in
conjunction with one or more peripheral (e.g., integrated circuit)
data and signal processing devices. In general, any device or
assembly of devices on which a finite state machine capable of
implementing the procedures described herein can be used as the
controller. A distributed processing architecture can be used for
maximum data/signal processing capability and speed.
[0051] While the invention has been described with reference to
preferred embodiments thereof, it is to be understood that the
invention is not limited to the preferred embodiments or
constructions. To the contrary, the invention is intended to cover
various modifications and equivalent arrangements. In addition,
while the various elements of the preferred embodiments are shown
in various combinations and configurations, which are exemplary,
other combinations and configurations, including more, less or only
a single element, are also within the spirit and scope of the
invention.
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