Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
HYBRID VEHICLE, HYBRID VEHICLE DRIVING SYSTEM AND
METHOD OF DRIVING HYBRID VEHICLE
TECHNICAL FIELD
The present invention relates to a hybrid vehicle
having a driving system including an internal combustion
I
engine and another power source, a hybrid vehicle driving
system, and a method of driving a hybrid vehicle.
BACKGROUND TECHNOLOGY
There have been proposed hybrid vehicles having a
driving system including an engine and another power source,
such as an electric motor.
Hybrid electric vehicles (hereinafter abbreviated to
"HEVs")provided with an engine and an electric motor are
classified by the type of a driving system into series HEVs
(hereinafter abbreviated to "SHEVs") and parallel HEVs
(hereinafter abbreviated to "PHEVs"). In the SHEV, an
engine drives a generator to generate electric energy, and
a motor is driven by the electric energy to drive wheels.
In the PHEV, an engine and a motor are used for driving
wheels.
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I~ a vehicle provided with only an engine, the
engine is unable to operate efficiently during idling and
during low-speed low-load condition, and there is a limit
to the reduction of fuel consumption. A vehicle provided
with only a motor must be loaded with heavy batteries for
storing electricity, have a large vehicle weight and is
unable to travel a long distance before the batteries are
exhausted.
The HEV compensates those drawbacks in the vehicle
provided with only an engine and the vehicle provided with
only a motor, and is able to make the most of their
advantages. During idling and low-speed low-load condition,
in which the engine is unable to operate efficiently, only
the motor is used, and changes the power source from the
motor to the engine as vehicle speed increases.
The engine is able to operate efficiently and, when
an increased torque is required temporarily for
acceleration or the like, the output torque of the motor
having high response characteristics is used additionally.
A HEV disclosed in Japanese Patent Laid-open No. Hei
8-294205 is provided with a lean-burn engine.
This engine is able to operate in either a
stoichiometric mode in which a mixture of a stoichiometric
air-fuel ratio is supplied to the engine or a lean-burn
mode in which a lean mixture is supplied to the engine.
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This engine is controlled so as to operate in the lean-burn
mode for most part of an operating time to maintain the
efficiency of the engine as high as possible.
This prior art HEV, however, supplies electric
energy from batteries to the motor when the torque of the
motor is necessary. Therefore, the operating mode of the
engine must be changed from the lean-burn mode to the
i
stoichiometric mode when the batteries are charged
insufficiently and the engine is unable to operate
continuously in the lean-burn mode.
DISCLOSURE OF THE INVENTION
In view of the foregoing problems, it is an object
of the present invention to provide a hybrid vehicle
driving system capable of making an engine mounted on a HEV
operate continuously as long as possible in the lean-burn
mode in which the engine is able to operate at a high
efficiency.
Even if the batteries are sufficiently charged, the
operating mode must be changed from the lean-burn mode to
the stoichiometric mode when a high torque is required.
There is a transient combustion range in which a large
amount of NOx is produced between a lean-burn range and a
stoichiometric combustion range. If the operating mode of
the engine is changed directly from that in the lean-burn
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range to that in the stoichiometric combustion range to
skip an operation in the transient combustion range, the
output torque of the engine changes suddenly to produce a
torque shock.
To solve such a problem, it is a second object of
the present invention to provide a driving method capable
of making the most use of the characteristics of the HEV to
add the output torque of a motor to the output torque of an
t
engine, of changing the operating mode of the engine from
that in the lean-burn range to that in the stoichiometric
combustion range without producing.NOx and without
producing any torque shocks.
Compression ignition techniques for gasoline engines
have made a rapid progress in recent years. However, any
compression ignition engine capable of producing torques
sufficient for driving a vehicle has not been developed.
Accordingly, it is a third object of the present
invention to provide an automobile capable of producing a
torque sufficient for driving a vehicle by a compression
ignition engine capable of producing a low torque.
The first object of the present invention can be
achieved by a hybrid vehicle driving system having a power
transmitting means for selectively transmitting the output
torque of an electric motor, the output torque of an
internal-combustion engine or a composite torque produced
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by combining the output torques of the internal-combustion
engine and the electric motor to driving wheels, comprising
a turbogenerator capable of converting the energy of
exhaust gas discharged from the internal-combustion engine
into electric energy, and an electrical connecting means
for electrically connecting the turbogenerator to the
electric motor.
The second object of the present invention can be
achieved by a hybrid vehicle driving method comprising
operating an internal-combustion engine selectively in a
first operating mode in which a mixture of an air-fuel
ratio not lower than a predetermined first air-fuel ratio
is supplied to the internal-combustion engine or a second
operating mode in which a mixture of an air-fuel ratio not
higher than a predetermined second air-fuel ratio and lower
than the first air-fuel ratio is supplied to the internal-
combustion engine, and driving wheels by a composite torque
produced by combining the respective output torques of the
internal-combustion engine and an electric motor, wherein
the electric motor is driven and the air-fuel ratio of the
mixture supplied to the internal-combustion engine is
maintained at the first air-fuel ratio when the air-fuel
ratio decreases below the first air-fuel ratio while the
internal-combustion engine is operating in the first
operating mode.
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The second object can be achieved also by estimating
a second air-fuel ratio engine torque that may be produced
by the internal-combustion engine when a mixture of the
second air-fuel ratio would be supplied to the internal-
combustion engine, calculating a torque difference between
an engine torque that may be produced when a mixture of the
first air-fuel ratio is supplied to the engine and the
estimated second air-fuel ratio engine torque, and changing
the operating mode from the first operating mode to the
second operating mode when the output torque of the
electric motor is approximately equal to the calculated
torque difference.
The third object can be achieved by a hybrid vehicle
comprising an internal-combustion engine capable of
operating in a compression ignition mode, a generator
capable of converting the output energy of the internal-
combustion engine into electric energy, and an electric
motor capable of converting the electric energy generated
by the generator into driving energy for driving wheels.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a hybrid vehicle
driving system in a first embodiment according to the
present invention.
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Fig. 2 is a diagram of assistance in explaining a
method of determining a desired driving torque for the
hybrid vehicle driving system shown in Fig. 1.
Fig. 3 is a diagram of assistance in explaining an
engine operating mode for the hybrid vehicle driving system
shown in Fig. 1.
Fig. 4 is a diagram of assistance in explaining.a
motor operating mode for the hybrid vehicle driving system
shown in Fig. 1.
Fig. 5 is a diagram of assistance in explaining
series/parallel modes in which the hybrid vehicle driving
system shown in Fig. 1 operates.
Fig. 6 is a diagram showing regions for the
operation of the engine shown in Fig. 1 at a minimum fuel
consumption.
Fig. 7 is a time chart of assistance in explaining
the variation of parameters when the operating condition of
the hybrid vehicle driving system shown in Fig. 1 changes.
Fig. 8 is a graph showing the response
characteristics of the change of condition for the hybrid
vehicle driving system shown in Fig. 1.
Fig. 9 is a graph showing the relation between
engine torque and the amount of discharged NOX when air-
fuel ratio for a hybrid vehicle shown in Fig. 1 is changed.
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Fig. 10 is flow chart of a motor-assistance control
procedure to be carried out when changing air-fuel ratio by
the hybrid vehicle driving system shown in Fig. 1.
Figs. 11A and 11B are pictorial views of assistance
in explaining power transmitting lines when the hybrid
vehicle shown in Fig. 1 operates in a regenerative braking
mode.
Fig. 12 is a flow chart of a control procedure to be
i
carried out for controlling the hybrid vehicle shown in Fig.
1.
Fig. 13 is a block diagram of a hybrid vehicle
driving system in a second embodiment according to the
present invention.
Fig. 14 is a diagram of assistance in explaining a
motor-drive mode for the hybrid vehicle driving system
shown in Fig. 13.
Figs. 15A and 15B are pictorial views of assistance
in explaining power transmitting lines when the hybrid
vehicle shown in Fig. 13 operates in a regenerative braking
mode.
Fig. 16 is a flow chart of a control procedure to be
carried out by the hybrid vehicle driving system shown in
Fig. 13.
Fig. 17 is a block diagram of a hybrid vehicle
driving system in a third embodiment according to the
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present invention.
Fig. 18 is diagram of assistance in explaining an
engine-drive mode for the hybrid vehicle driving system
shown in Fig. 17.
Fig. 19 is diagram of assistance in explaining a
motor-drive mode for the hybrid vehicle driving system
shown in Fig. 17.
Fig. 20 is a diagram of assistance in explaining a
i
series/parallel mode for the hybrid vehicle driving system
of Fig. 17.
Fig. 21 is a time chart of assistance in explaining
the variation of parameters when the operating condition of
the hybrid vehicle driving system shown in Fig. 17 changes;
Fig. 22 is a flow chart of a control procedure to be
carried out by the hybrid vehicle driving system shown in
Fig. 17.
Fig. 23 is a sectional view of a turbogenerator to
be employed in an embodiment of the present invention.
Fig. 24 is a graph showing the exhaust heat
recovering ability of the turbogenerator shown in Fig. 23.
Fig. 25 is a diagram showing the relation between
accelerator pedal displacement, brake pedal displacement,
driving torque and regenerative torque.
Fig. 26 is a graph showing change of operating
condition.
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Fig. 27 is a graph showing change of operating
condition.
Fig. 28 is a graph showing operating condition
change.
Fig. 29 is a time chart showing operating condition
change (Y -~ Z) with time.
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will
be described with reference to the accompanying drawings.
Fig. 1 shows a HEV driving system in a first
embodiment according to the present invention. The HEV
driving system comprises an engine 10, a generator 17 for
generating electric energy by an engine torque driven by
the engine 10, a motor/generator 19 that receives electric
energy and produces a motor torque, and a turbogenerator 7
incorporated into an exhaust system 9 for the engine 10 to
receive the energy of exhaust gas for power generation.
The HEV driving system further comprises a power
transmission changing mechanism 12 comprising a planetary
gear for distributing the output of the engi~le 10 to the
generator 17 and a drive shaft 21, a power transmission
change mechanism 22 for combining the output of the
i
motor/generator 19 and the output of the drive shaft 21, an
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electric energy converter 8 for controlling the voltage of
electric energy generated by the turbogenerator 7, an
electric energy converter 16 for controlling the voltage of
electric energy generated by the generator 17, an electric
energy converter 18 for supplying electric energy to the
motor/generator 19, an electric energy storage device 5
connected to the electric energy converters to store
electric energy, and an electric energy converter
1
controller 1 for controlling the voltages of the electric
energy converters and controlling a charging operation for
charging the electric energy storage device.
The engine 10 is provided with an electronically
controlled throttle valve, not shown, which is fully open
while the engine 10 is in a normal operation. A
nonthrottle engine not provided with any throttle valve may
be used instead of the engine 10. Thus, pump loss, which
i reduces thermal efficiency, is not produced. The output
torque of the engine 10 is controlled through the control
of air-fuel ratio, i.e., through the control of fuel supply
amount. The engine thus controlled is, for example, a
diesel engine. However, a diesel engine is not preferable
because a diesel engine produce smoke when the same
operates in a high-load operating range. According to the
present invention, the engine 10 is assumed to be a lean-
burn gasoline engine. Preferably, the engine is a lean-
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burn engine of a cylinder injection type, in which the fuel
is injected directly into a combustion chamber, capable of
operating at a high air-fuel ratio of about fifty at a
maximum. When the air-fuel ratio is not smaller than fifty,
the mixture is ignited for combustion by compression
ignition system that ignites a homogeneous mixture by heat
of compression. A compression-ignition engine is described
in detail in Japanese Patent Laid-open No. Hei 10-56413.
The operation of the first embodiment of the present
invention will be described hereinafter. Fig. 2 is a
diagram of assistance in explaining a method of determining
a desired driving torque for a HEV provided with the HEV
driving system shown in Fig. 1. The desired driving torque
is a torque to be transmitted to a driving wheel to drive
the HEV for traveling and is the sum of an engine torque
and a motor torque.
A desired driving torque is dependent on accelerator
pedal displacement, brake pedal displacement and the
traveling speed of the HEV. Accelerator pedal displacement
and brake pedal displacement reflect the driver's intention
of acceleration and driver's intention of deceleration,
respectively, and represent desired output torques,
respectively. The desired driving torque increases as the
accelerator pedal displacement increases, and the desired
torque decreases (regenerative torque increases) as the
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brake pedal displacement increases. The relation between
those factors varies with the traveling speed. The amount
of change of the driving torque with the accelerator pedal
displacement and that of the driving torque with the brake
pedal displacement are small when the traveling speed is
high.
Fig. 3 shows an engine operating mode for the engine
of the HEV in this embodiment. The engine operating mode
i
is determined on the basis of traveling speed and desired
driving torque. The operating mode is divided roughly into
regions A, B and C. Values of traveling speed and desired
torque are normalized by maximum values for the HEV in this
embodiment. In the region A, the engine is not operated
and only the motor 19 is used for traveling until traveling
speed reaches a predetermined traveling speed V1 (Fig. 3).
If the amount of electric energy stored in the electric
energy storage device 5 is insufficient or decreases, the
engine 10 is operated in the compression ignition mode to
generate power by the generator 17. In this state, the
engine speed of the engine 10 is kept constant, the
throttle valve is fully opened, and generator driving power
is controlled only through the control of fuel feed amount.
This control is achieved by controlling power generating
amount by an engine controller 11 for controlling the
engine 10 on the basis of information provided by a main
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controller 15. If the desired driving torque is high and
the electric energy requirement of the motor/generator 19
is large in the region A; the operating mode is changed to
a stratified charge combustion mode (region A2) or a
homogeneous charge combustion mode (region A3). A very
lean mixture having an air-fuel ratio of 50 or above
(superlean mixture) is used for the compression ignition
mode, a lean mixture having an air-fuel ratio in the range
t
of 30 to 50 (lean mixture) is used for the stratified
charge combustion mode, and a stoichiometric mixture having
an air-fuel ration in the range of 14 to 15 (stoichiometric
mixture) is used for the homogeneous charge combustion mode.
In a region B, the traveling speed is in the range
of Vl and V3, the desired driving torque is not higher than
T2, the engine is operated in the stratified charge
combustion mode and the air-fuel ratio is in the range of
30 to 50.
In a region C, the air-fuel ratio is stoichiometric,
and the engine 10 is operated in the homogeneous charge
combustion mode to increase the engine torque.
Fig. 4 shows a motor operating mode for the HEV in
this embodiment. The motor operating mode is determined on
the basis of traveling speed and desired driving torque.
The operating mode is divided roughly into regions A, D, E
and F. Values of traveling speed and desired torque are
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normalized by maximum values for the HEV in this embodiment.
In the region A, the engine is not operated and only the
motor 19 is used for traveling until the traveling speed
reaches a predetermined traveling speed Vl (Fig. 4).
Electric energy for driving the motor 19 is supplied from
the electric energy storage device 5. If the amount of
electric energy stores in the electric energy storage
device 5 is insufficient or decreases, the engine 10 is
operated in the compression ignition mode to generate power
by the generator 17 and electric energy thus generated is
supplied to the motor 19. This control is achieved by
controlling power generating amount by the engine
controller 11 for controlling. the engine 10 and an electric
energy converter controller 1 on the basis of information
provided by the main controller 15.
In the region D, traveling speed is in the range of
Vl to V2, desired driving torque is not higher than T1,
only the engine is used for traveling and the motor is not
operated.
In the region E, the turbogenerator 7 is driven by
the energy of the exhaust gas discharged from the engine 10
to generate electric energy. The electric energy thus
generated is used for driving the motor 19 as needed or is
used for charging the electric energy storage device 5.
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In the region F, the turbogenerator 7 is driven by
the energy of the exhaust gas discharged from the engine 10.
the generator l7 is driven by the engine 10 to increase
power generating amount, and the motor 19 is driven by the
thus generated electric energy.
In this embodiment, energy is recovered by the
turbogenerator 7 in the regions E and F where engine torque
and engine speed are relatively high. As obvious from Fig.
1
24 which will be described later, the higher the engine
torque, the greater is the amount of recovered waste heat.
The conventional automobile recovers energy from
exhaust heat produced by the engine by a turbosupercharger
and a turbogenerator. Although the turbosupercharger is
able to compress intake air, energy recovered by the
turbosupercharger cannot be stored. Energy recovered by
the turbogenerator can be stored as electric energy in
batteries.
Since the hybrid vehicle is provided with a motor
that uses electric energy as a driving means, it is
preferable that the hybrid vehicle is provided with a
turbogenerator, the hybrid vehicle enables inclusive energy
management, and the hybrid vehicle operates at improved
efficiency.
Fig. 5 shows operating modes for the HEV sorted on
the basis of series/parallel conception. Basically, the
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engine 10 is not operated and only the motor/generator 19
produces driving power in a region A. In this state, the
HEV operates as an electric vehicle.
When the electric energy storage device 5 is
insufficiently charged or the energy stored in the electric
energy storage device 5 decreases, the engine 10 is
operated in the compression ignition mode to drive the
generator 17, electric energy generated by the generator 17
s
is supplied to the motor/generator 19. Consequently, the
HEV operates as an SHEV when the electric energy is charged.
In a region B, only the engine 10 produces driving
power. The HEV operates as an automobile provided with an
ordinary internal-combustion engine. A mixture of an air-
fuel ratio in the range of 30 to 50 is supplied to the
engine 10 to operate the engine 10 in the stratified charge
combustion mode. Therefore the efficiency is not reduced.
The energy of the exhaust gas is recovered and used by the
turbogenerator 7 for power generation.
In a region B', a mixture having an air-fuel ratio
of 30 is supplied to the engine 10 for constant operation,
and the driving torque is supplemented by the torque of the
motor/generator 19. Most part of the electric energy for
driving the motor/generator 19 is generated by the
turbogenerator 7 and hence the amount of electric energy
stored in the electric energy storage device 5 is not
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affected by the operation of the motor/generator 19. In
this respect, the HEV is a PHEV that uses the output
torques of both the engine 10 and the motor/generator 19.
Since the HEV uses electric energy generated by the
turbogenerator 7 for driving the motor/generator 19, the
HEV is an SHEV.
In a region C', a mixture having an air-fuel ratio
in the range of 14 to 15 is supplied to the engine 10 and
r
the engine 10 operates constantly in the homogeneous charge
combustion mode. Driving torque is supplemented with the
output torque of the motor/generator 19. Most part of
electric energy supplied to the motor/generator 19 is
electric energy generated by the turbogenerator 7 and hence
the amount of electric energy stored in the electric energy
storage device 5 is not affected by the operation of the
motor/generator 19. Thus, the HEV operates as both a PHEV
and an SHEV as the same operation as the region B'.
In the region C, the generator 17 is operated to
increase power generating amount, and electric energy
generated by both the turbogenerator 7 and the generator 17
is used: In this region, the HEV operates as a PHEV that
uses the output torques of both the engine 10 and the
motor/generator 19, and as an SHEV that uses electric
energy generated by the turbogenerator 7 for driving the
motor/generator 19.
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Fig. 6 shows characteristics of the engine for the
HEV in this embodiment. Fig. 6 shows the dependence of
fuel consumption on engine speed and engine torque, and
ranges in which the engine operates at a minimum fuel
consumption rate in each operating mode. An ordinary
engine the output torque of which is controlled by
regulating the amount of air by a throttle valve has a
single range in which the engine is able to operate at a
l
minimum fuel consumption rate. The fuel consumption rate
of the engine increases in an operating range in which the
engine speed and load on the engine are low. The engine in
this embodiment for the HEV is able to operate selectively
in one of the compression ignition mode, the stratified
charge combustion mode and the homogeneous charge
combustion mode. Therefore, the engine operates at the
minimum fuel consumption rate in three ranges as shown in
Fig. 6. In a region G, the engine operates in the
compression ignition mode and air-fuel ratio for Dl is
about 50. In a region H, the engine operates in the
stratified charge combustion mode, air-fuel ratio is about
40 for E1 and about 30 for E2. In a region J, the engine
operates in the homogeneous charge combustion mode and air-
fuel ratio is about 15 for F1 and about 14 for F2. Air-
fuel ratio is thus determined for each operating mode and
engine speed is controlled so that fuel consumption rate is
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in a minimum fuel consumption rate range.
Fig. 7 is a time chart showing control operations of
a control system. A characteristic operation of this
embodiment will be described on an assumption that
operating condition changed from that indicated by a point
X to that indicated by a point Y in Fig. 5.
While the HEV is traveling under conditions in the
region A, the engine 10 is stopped when the electric energy
storage device is fully charged or the engine 10 is
operated in the compression ignition mode if the electric
energy storage device 5 is insufficiently charged, and an
engine torque Tel indicated by dotted line 30 is produced.
The engine torque Tel is not used directly for driving the
vehicle; the same is used to drive the generator 17 for
power generation. Therefore, air-fuel ratio is infinity
while the engine 10 is stopped and is about 50 as indicated
by dotted line 31 while the engine 10 is in operation. In
the region A, the vehicle is driven by the motor/generator
19 and the motor produces a torque Tml. An output torque
T1 equal to the torque Tml is transmitted to the driving
wheel. When the accelerator pedal displacement is changed
from al to a2, a desired driving torque is calculated on
the basis of information about the change of the
accelerator pedal displacement and the traveling speed, and
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the driving toque is changed from Tol to To2. During the
change of the desired driving torque from that at the point
X to that at the point Y (Fig. 5), the output driving
torque changes through those in the regions B and B' to
that in the region C. When operating condition changes
from that in the region A to that in the region B, air-fuel
ratio is determined so that the engine kept stopped or
operating to produce the torque Tel for power generation is
I
operated in the stratified charge combustion mode to
produce an engine torque Te2. The torque of the
motor/generator 19 is decreased gradually until the air-
fuel ratio of the mixture supplied to the engine 10
coincides with a set air-fuel ratio. The output torque of
the motor/generator 19 is adjusted by adjusting a current.
The motor torque is reduced by reducing the current. In
this state, the motor may continue to run by inertia. In
the region B, the motor torque is reduced to naught upon
the coincidence of the air-fuel ratio of the mixture
supplied to the engine 10 with the set value. When the
operating condition changes from that in the region B to
that in the region B', a mixture having an air-fuel ratio
of 30 is supplied to the engine 10, the engine 10 continues
to operate at a fixed engine speed in the stratified charge
combustion mode to increase the output torque of the
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motor/generator 19. Thus, the engine 10 is assisted by the
motor/generator 19, the engine 10 is able to continue the
operation in the stratified charge combustion mode and
hence fuel consumption rate can be improved. Since
electric energy generated by the turbogenerator 7 is used
for driving the motor/generator 19, the amount of electric
energy stored in the electric energy storage device 5 does
not change. In the region C, the engine 10 operates in the
homogeneous charge combustion mode. Consequently, an
engine torque Te3 produced by the engine in the homogeneous
mixture combustion mode differs from the engine torque Te2
produced by the engine in the stratified charge combustion
mode by a torque difference OTe. A conventional engine
system not provided with any motor-assist mechanism adjusts
the output by reducing the flow of air through the throttle
valve so as to reduce the torque difference ~Te, which,
however, produces a negative pressure in the cylinders and
produces a pump loss.
In this embodiment, the operating condition is
changed from that in the region B' to that in the region C
when the torque of the assisting motor became approximately
equal to the torque difference DTe. A control operation
for changing the operating condition will be described with
reference to Fig. 9. A period where the operating
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condition is in the region 8', time for which the
motor/generator 19 is operated for torque assist, is
determined on the basis of the accelerator pedal
displacement. Since time in which the accelerator pedal
displacement changes from al to a2 is conceived to be a
desired value of output driving torque response time
desired by the driver, a short period (Ta2 - Tal) signifies
quick acceleration and a relatively long period (Ta2 - Tal)
signifies slow acceleration. Therefore, in a period (t4 -
t3) in the region B' is determined as shown in Fig. 8
according to the period (Ta2 - Tal). When the operating
condition is changed to that in the region C, a mixture
having an air-fuel ratio of 15 is supplied to the engine 10
and the engine 10 continues to operate at a fixed engine
speed in the homogeneous charge combustion mode. The motor
torque produced by the motor/generator 19 drops by OTe and
current command is small immediately after the change of
the operating condition. Subsequently, the motor torque of
the motor/generator 19 is increased until the desired
driving torque is produced. When it is desired to make the
generator 17 generate power in the region C, the air-fuel
ratio is changed to an air-fuel ratio of 14 as indicated by
dotted line to increase the engine torque as indicated by
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dotted line 32.
Control operations for changing the operating
condition from that in the region B' to that in region C
will be described with reference to Fig. 9. The output
characteristic of the engine for the HEV in this embodiment
is represented by the relation between air-fuel ratio and
engine torque. In a range where air-fuel ratio is 50 or
above, the engine is operated in the compression ignition
mode in the region A to make the generator 17 generate
power. When the generator 17 does not generate any power,
the engine torque is naught. A range where air-fuel ratio
is in the range of 30 to 50 corresponds to the stratified
charge combustion mode, and a range where air-fuel ratio is
in the range of 14 to 15 corresponds to the homogeneous
charge combustion mode. A range where air-fuel ratio is in
the range of 30 to 15 is not used because a large amount of
NOx is produced when the engine is operated in that range.
The engine for the HEV of the present invention is
provided with an electronically controlled throttle.
However, the flow of air is not varied and fuel supply
amount is varied to control engine torque to operate the
engine at a high efficiency. Therefore, when air-fuel
ratio is changed from 30 to 15, the engine torque changes
by a torque change ~Te.
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If air-fuel ratio is thus changed, operating
performance becomes worse and it is possible that a driving
force transmitting system is broken. The present invention
compensates the torque change by the motor torque so that
torque is transmitted smoothly to the driving wheel when
air-fuel ratio is changed. Since electric energy supplied
to the motor/generator 19 in compensating the torque change
is generated by the turbogenerator 7 by using energy
l
recovered from the exhaust gas. Therefore, the amount of
electric energy stored in the electric energy storage
device 5 is not affected by the change of air-fuel ratio.
A changing method will more concretely be described. The
engine 10 starts operating in a constant operation mode and
the motor/generator 19 starts producing motor torque after
air-fuel ratio reached 30. Since the motor produces motor
torque according to a current command, torque can smoothly
be produced by minutely controlling the current command.
Consequently, the torque change does not cause any problem.
Timing of changing air-fuel ratio from 30 to 15 is
determined so that air-fuel ratio is changed when a motor
torque ~Tm coincides with the engine torque change ~Te.
Upon the change of air-fuel ratio, the electric energy
converter controller 1 reduces the value of the current
command given to the motor/generator 19 to reduce the motor
CA 02326849 2000-10-26
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torque corresponding to the engine torque change 4Te. If
the changing timing is too late,
OTm > OTe ... (1)
and the output driving torque changes stepwise. If the
output driving torque drops even for a moment after the
change of air-fuel ratio, operating performance and a
sensation of acceleration are spoiled. Therefore timing of
i air-fuel ratio change must be determined so as to meet:
~Tm ~ Te ... (2)
Motor torque can accurately be known through the
measurement of a current. Engine torque can be estimated
from fuel feed amount, intake air supply amount and engine
speed. An engine torque when fuel feed amount is increased
while a mixture having an air-fuel ratio of 30 is supplied
to the engine is estimated. If an estimated engine torque
is excessively high, the motor/generator controls ~Tm on
the basis of a wrong OTe' different from the actual engine
torque change DTe and a state represented by Expression (1)
may occur. Therefore, the relation between the estimated
engine torque change OTe' and the motor torque ~Tm is
expressed by:
OTm = ~ x ~Te' ... (3)
CA 02326849 2000-10-26
- 27 -
and the value of ~ is adjusted so that the estimated engine
torque change ~Te' approaches the actual engine torque
change ~Te.
Fig. 10 shows a control procedure to be carried out
when changing the air-fuel ratio. When a motor-assisted
operation control operation is started in block 40, the
main controller 15 stores time data indicating the time
when the motor-assisted operation control operation is
started in a storage device included in a control unit in
block 41. In block 42, engine torque at present (air-fuel
ratio . 30) is calculated on the basis of fuel feed amount,
intake air supply amount and engine speed. In block 43,
engine torque when air-fuel ratio is 15 is estimated on the
basis of the calculated result. At the beginning of the
first cycle of the air-fuel ratio change control operation,
the correction coefficient ~ for correcting an estimated
engine torque is given in block 44. When learned value of
the correction coefficient ~ is stored in the storage
device included in the control unit, reference is made to
the learned value of the correction coefficient ~ in block
46 and the value of the correction coefficient ~ is
determined in block 45. The motor torque change ~Tm is
calculated by using Expression (3) in block 47, and a
CA 02326849 2000-10-26
- 28 -
current I' that produces the motor torque change OTm is
calculated. In block 48, motor current I is measured, and
the motor current I is compared with the motor current I'
in block 49. If the motor current I and I' are different
from each other, the motor current I is measured again 1n
block 48 and is compared with the motor current I' in block
49. When I = I', an air-fuel ratio change~command
requesting changing air-fuel ratio from 30 to 15 is given
to the controller il of the engine 10. In block 51, change
in the driving wheel is measured to decide whether or not
the correction coefficient ~ for correcting the estimated
engine torque is appropriate. The change in the rotation
of the driving wheel is measured by a torque sensor
attached to a propeller shaft or a wheel speed sensor
included in an antilock brake system (ABS). Since a torque
sensor measures an actual torque being transmitted to the
driving wheel, it can be decided that the output driving
torque has smoothly changed. A wheel speed sensor measures
a change in rotating speed when the output driving torque
changes stepwise. Change in the output driving torque can
be measured by either a torque sensor or a wheel speed
sensor. In block 52, a set of data including a change in
the output driving torque, a fuel feed amount, an intake
air supply amount, an engine speed, an estimated engine
CA 02326849 2000-10-26
- 29 -
torque difference and a motor torque is stored in the
storage device for learning control. Therefore, the
accuracy of the correction coefficient ~ is improved by
leaning control. After the completion of the motor-
assisted air-fuel ratio change control operation, the
control procedure returns to a main control procedure.
Figs. 11A and 11B show the condition of power
transmitting lines when the brake system of the HEV is
operated. In the HEV, a braking force proportional to the
brake pedal displacement is produced as shown in Fig. 2.
In this specification, the braking force is equal to the
sum of a braking force produced by a mechanical brake
system of the vehicle, a regenerative braking force
produced by the motor/generator 19 and an engine-braking
force. As shown in Fig. 11A, rotational energy of a
mechanism on the side of the wheels is used to drive the
motor/generator 19 for regenerative braking when the
electric energy storage device 5 has empty capacity (when
the electric energy storage device 5 is not fully charged).
As shown in Fig. 11B, rotational energy of the mechanism on
the side of the wheels is used to drive the engine when the
electric energy storage device has a little empty capacity
(when the electric energy storage device 5 is fully
charged). In this state, the electronically controlled
CA 02326849 2000-10-26
- 30 -
throttle is fully closed to produce negative pressures in
the cylinders of the engine in order that the braking
effect of the engine is enhanced.
Fig. 12 shows a control procedure in this embodiment.
In block 60, an operating condition of the HEV is
determined on the basis of a set of data including an
accelerator pedal displacement, a brake pedal displacement
and a traveling speed; and a desired driving torque is
calculated in block 61. In block 62, an operating mode is
determined on the basis of the desired driving torque and
the traveling speed. In the region A, the amount of
electric energy stored in the electric energy storage
device 5 is checked in block 63. If the electric energy
storage device 5 is insufficiently charged, the engine 10
is operated in the compression ignition mode in block 64 to
generate power by the generator in block 69. If the
electric energy storage device 5 is fully charged, the
engine 10 is stopped. When the engine 10 is operated, the
electric energy converter controller 1 gives a voltage
control signal to the electric energy converter 16 of the
generator 17. Since the generator 17 is assumed to be an
ac generator, the electric energy converter 16 is an ac-do
converter for converting ac electric energy generated by
the generator 17 into corresponding do electric energy. If
the generator 17 is a do generator, the electric energy
CA 02326849 2000-10-26
- 31 -
converter 16 is a dc-do converter, and the controller 1
executes a voltage changing control operation to change a
voltage to a predetermined voltage. As shown in block 74,
the motor/generator 19 produces a driving force for
traveling in the region A.
In the region B, the engine 10 is operated in the
stratified charge combustion mode in block 65 and the
motor/generator 19 does not produce any driving force. In
I
block 68, the amount of electric energy stored in the
electric energy storage device 5 is checked. If the
electric energy storage device 5 is insufficiently charged,
power is generated by the turbogenerator 7 combined with
the exhaust pipe 9 of the engine 10 to charge the electric
energy storage device 5. The region B has a special region
B' for special conditions, i.e., transient conditions under
which the engine 10 is operated when the operating
condition of the engine changes from that in the region B
to that in the region C. In the region B', the engine 10
operates constantly in the stratified charge combustion
mode and the motor/gene~ator 19 is driven to assist the
engine 10 for providing a desired torque.
In the region C, the engine 10 is operated in the
homogeneous charge combustion mode in block 66, the
motor/generator 19 is driven in block 76 to provide an
supplementary torque. Electric energy is supplied to the
CA 02326849 2000-10-26
- 32 -
motor/generator 19 only by the turbogenerator 7 in the
region C', and by both the turbogenerator 7 and the
generator 17 in the region C.
Basically, the motor/generator 19 recovers energy in
block 73 when the brake system is operated. When it is
confirmed in block 63 that the electric energy storage
device 5 is fully charged, the motor/generator 19 is not
used for regenerative braking operation and the braking
1
effect of the engine 10 is used in block 67. In any one of
those modes, the output driving torque T is measured in
block 77 and the foregoing operations are repeated until
the output driving torque T coincides with the desired
driving torque To.
Another embodiment of the present invention will be
described. Fig. 13 shows an HEV driving system in a second
embodiment according to the present invention. The HEV
driving system comprises an engine 10, a motor/generator 17
interposed between the engine 10 and a clutch 12, a
motor/generator 19 independent of the engine 10, and a
turbogenerator 7 combined with the exhaust system 9 of the
engine 10 to generate power by using the energy of the
exhaust gas. The HEV driving system further comprises a
power transmission change mechanism 22 for combining the
output of the motor/generator 19 and the output of the
engine 10 transmitted by a drive shaft 21, an electric
CA 02326849 2000-10-26
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energy converter 8 for controlling the voltage of electric
energy generated by the turbogenerator 7, an electric
energy converter 16 for controlling the voltage of electric
energy generated by the motor/generator 17, an electric
energy converter 18 for supplying electric energy to the
motor/generator 19, an electric energy storage device 5
connected to the electric energy converters to store
electric energy, and an electric energy converter
controller 1 for controlling the voltages of the electric
energy converters and controlling a charging operation for
charging the electric energy storage device. Desirably,
the engine is similar to that included in the first
embodiment.
The operation of the second embodiment will
concretely be described hereinafter. A method of
determining a desired driving torque for an HEV driven by
the HEV driving system shown in Fig. 3 is the same as that
previously explained with reference to Fig. 2. Engine
operating modes and series/parallel modes for the engine of
the HEV in this embodiment are the same as those previously
described with reference to Figs. 3 and 5. Fig. 14 shows a
motor operating modes. The motor operating mode is
determined on the basis of traveling speed and desired
driving torque. The motor operating mode is divided
roughly into regions A, D, E and F. Values of traveling
CA 02326849 2000-10-26
- 34 -
speed and desired driving torque are normalized by maximum
values for the HEV in this embodiment. In the region A,
the engine is not operated and only the motor 19 is used
for traveling until traveling speed reaches a predetermined
traveling speed V1 (Fig. 14). The electric energy storage
device 5 supplies electric energy for driving the motor 19.
If the amount of electric energy stored in the electric
energy storage device 5 is insufficient or decreases, the
1
engine 10 is operated in the compression ignition mode to
generate power by the generator 17 and electric energy
generated by the generator 17 is used for driving the motor
19. This control is achieved by controlling power
generating rate by an engine controller 11 for controlling
the engine 10 and the electric energy converter controller
1 on the basis of information provided by a main controller
15.
In the region D, where traveling speed is in the
range of Vl to V2, and desired driving torque is not higher
than T1, only the engine is used for traveling and the
motor is not operated.
In the region E, the turbogenerator 7 is driven by
the energy of the exhaust gas discharged from the engine 10,
electric energy generated by the turbogenerator 7 is used
for driving the motor 19 or for charging the electric
energy storage device 5.
CA 02326849 2000-10-26
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In the region F, the turbogenerator 7 is driven by
the energy of the exhaust gas discharged from the engine 10,
the motor/generator 17 is driven by the engine 10 to
increase power generating amount and electric energy
generated by the turbogenerator 7 and the motor generator
17 is used for driving the motor 19.
Figs. 15A and 15B show the condition of power
transmitting lines when the brake system of the HEV is
operated. In the HEV, a braking force proportional to the
brake pedal displacement is produced as shown in Fig. 2.
In this specification, the braking force is equal to the
sum of a braking force produced by a mechanical brake
system of the vehicle, a regenerative braking force
produced by the motor/generators 17 and 19, and an engine-
braking force. As shown in Fig. 15A, rotational energy of
a mechanism on the side of the wheels is used to drive the
motor/generator 19 for regenerative braking when the
electric energy storage device 5 has empty capacity (when
the electric energy storage device 5 is not fully charged).
As shown in Fig. 15B, rotational energy of the mechanism on
the side of the wheels is. transmitted through a power
transmission changing mechanism, a transmission and a
clutch to the motor/generator 17 and is used to increase
the regenerative braking force when the electric energy
storage device has little empty capacity. In Fig. 15B, the
CA 02326849 2000-10-26
- 36 -
energy of the mechanism on the side of the wheels is not
transmitted to the two motor/generators 17 and 19 and is
transmitted to the engine 10 when the electric energy
storage device 5 has little empty capacity (when the
electric energy storage device 5 is fully charged). In
this state, the electronically controlled throttle is fully
closed to produce negative pressures in the cylinders of
the engine in order that the braking effect of the engine
1
is enhanced.
Fig. 16 shows a control procedure in this embodiment.
In block 160, an operating condition of the HEV is
determined on the basis of a set of data including an
accelerator pedal displacement, a brake pedal displacement
and a traveling speed, and a desired driving torque is
calculated in block 161. In block 162, an operating mode
is determined on the basis of the desired driving torque
and the traveling speed. When the operating mode is in the
region A, the amount of electric energy stored in the
electric energy storage device 5 is checked in block 163.
If the electric energy storage device 5 is insufficiently
charged, the engine 10 is operated in the compression
ignition mode in block 164 to generate power by the motor
generator in block 169. If the electric energy storage
device 5 is fully charged, the engine 10 is stopped. When
the engine 10 is operated, the electric energy converter
CA 02326849 2000-10-26
- 37 -
controller 1 gives a voltage control signal to the electric
energy converter 16 of the motor/generator 17. Since the
motor/generator 17 is assumed to be an ac generator, the
electric energy converter 16 is an ac-do converter for
converting ac electric energy generated by the
motor/generator 17 into corresponding do electric energy.
If the motor/generator 17 is a do generator, the electric
energy converter 16 is a dc-do converter, and the
1
controller 1 executes a voltage changing control operation
to change a voltage to a predetermined voltage. As shown
in block 174, the motor/generator 19 produces a driving
force for traveling in the region A.
In the region B, the engine 10 is operated in the
stratified charge combustion mode in block 165 and the
motor/generator 19 does not produce any driving force. In
block 168, the amount of electric energy stored in the
electric energy storage device 5 is checked. If the
electric energy storage device 5 is insufficiently charged,
power is generated by the turbogenerator 7 combined with
the exhaust pipe 9 of the~engine 10 to charge the electric
energy storage device 5. The region 8 has a special region
B' for special conditions, i.e., transient conditions under
which the engine is operated when the operating condition
of the engine changes from that in the region B to that in
the region C. In the region B', the engine 10 operates
CA 02326849 2000-10-26
- 38 -
constantly in the stratified charge combustion mode and the
motor/generator 19 is driven to assist the engine 10 for
providing a desired torque.
In the region C, the engine 10 is operated in the
homogeneous charge combustion mode in block 166, the
motor/generator 19 is driven in block 176 to provide an
supplementary torque. Electric energy is supplied to the
motor/generator 19 only by the turbogenerator 7 in the
region C', and by both the turbogenerator 7 and the
generator 17 in the region C.
Basically, the motor/generators 17 and 19 recover
energy in blocks 173 and 179 when the brake system is
operated. When it is confirmed in block 163 that the
electric energy storage device 5 is fully charged, the
motor/generators 17 and 19 are not used for regenerative
braking operation and the braking effect of the engine 10
is used in block 167. In any one of those modes, the
output driving torque T is measured in block 177_and the
foregoing operations are repeated until the output driving
torque T coincides with the desired driving torque To.
A further embodiment of the present invention will
be descr3.bed. Fig. 17 shows an HEV driving system in a
third embodiment according to the present invention. The
HEV driving system comprises an engine 10, a
motor/generator 17 interposed between the engine 10 and a
CA 02326849 2000-10-26
- 39 -
clutch 12, and a turbogenerator 7 combined with the exhaust
system 9 of the engine 10 to generate power by using the
energy of the exhaust gas. A transmission 13 is connected
to the engine 10 and the output shaft of the
motor/generator 17. The HEV driving system further
comprises an-electric energy converter 8 for controlling
the voltage of electric energy generated by the
turbogenerator 7, an electric energy converter 16 for
i
controlling the voltage of electric energy generated by the
motor/generator, an electric energy storage device 5
connected to the electric energy converters to store
electric energy, and an electric energy converter
controller 1 for controlling the voltages of the electric
energy converters and controlling a charging operation for
charging the electric energy storage device. Desirably,
the engine is similar to that included in the first
embodiment.
The operation of the third embodiment will
concretely be described hereinafter. A method of
determining a desired driving torque for an HEV driven by
the HEV driving system shown in Fig. 17 is the same as that
previously explained with reference to Fig. 2. Engine
operating modes for the engine of the HEV in this
embodiment are shown in Fig. 18. The engine operating mode
is determined on the basis of traveling speed and desired
CA 02326849 2000-10-26
- 40 -
driving torque. The engine operating mode is divided
roughly into regions A, B and C. Values of traveling speed
and desired driving torque are normalized by maximum values
for the HEV in this embodiment. The engine 10 is operated
in the compression ignition mode, in the region A, in the
stratified charge combustion mode in the region B and the
homogeneous charge combustion mode in the region C. In
this state, the engine 10 is operated at a fixed engine
speed, the throttle valve is fully opened and the output of
the engine 10 is controlled by controlling only fuel feed
amount. This control is achieved by controlling power
generating amount by an engine controller ll for
controlling the engine 10 on the basis of information
provided by a main controller 15. The operating mode is
changed through the stratified charge combustion mode
(region A2) in which the fuel is injected into the
cylinders, to the homogeneous charge combustion mode
(region A3) to increase engine output. The air-fuel ratio
of the mixture is 50 or above (superlean mixture) for the
compression ignition mode, in the range of 30 to 50 (lean
mixture) for the stratified charge combustion mode, and in
the range of 14 to 15 (stoichiometric mixture) for the
homogeneous combustion mode.
In the region B, the traveling speed is in the
range of V1 to V3, the desired driving torque is not higher
CA 02326849 2000-10-26
- 41 -
than T2, the engine is operated in the stratified charge
combustion mode and the air-fuel ratio is in the range of
30 to 50.
In the range C, the air-fuel ratio is stoichiometric,
and the engine 10 is operated in the homogeneous charge
combustion mode to increase the engine torque.
Fig. 19 shows a motor operating mode for the HEV.
.The motor operating mode is determined on the basis of
traveling speed and desired driving torque. The operating
mode is divided roughly into regions D, E and F. Values of
traveling speed and desired torque are normalized by
maximum values for the HEV in this embodiment. In the
region E, assistive torque production is not performed and
power is generated continuously by using the output of the
engine. The region D included in the region E is a low-
engine-speed, low-load region. It is not desirable to
operate the engine in the region D from the viewpoint of
efficiency. Therefore, torque production is assisted by
the motor/generator 17. In the region F, torque production
must always be assisted by the motor/generator 17 and the
turbogenerator supplies electric energy.
Fig. 20 shows an operating mode for the HEV in this
embodiment. The operating mode is determined on the basis
of traveling speed and desired driving torque. The
operating made is divided roughly into regions O, P, Q, R
CA 02326849 2000-10-26
- 42 -
and S. Values of traveling speed and desired output
torque are normalized by maximum values for the HEV in this
embodiment.
Since the HEV driving system in this embodiment is
provided with only on motor/generator, the HEV cannot
operated as an SHEV. In the region O, the engine 10 is
operated in the compression ignition mode and the
motor/generator 17 produces an supplementary torque to
i
assist the engine 10. In the region P, the engine 10 is
operated in the compression ignition mode and the
motor/generator 17 generates power. In the region Q, the
engine 10 is operated in the stratified charge combustion
mode and the motor/generator 17 generates power. In the
region R, the engine 10 is operated in the stratified
charge combustion mode, the turbogenerator 7 generates
power and the motor/generator 17 produces an supplementary
torque to assist the engine 10. In the region S, the
engine is operated in the homogeneous charge combustion
mode, the turbogenerator generates power and the
motor/generator 17 produces an supplementary torque to
assist the engine 10.
Fig. 21 is a time chart showing control operations
of a control system. A characteristic operation of this
embodiment will be described on an assumption that the
desired output torque changed from a value indicated by a
CA 02326849 2000-10-26
- 43 -
point X to that indicated by a point Y in Fig. 20. While
the engine 10 is stopped in a condition in the region O,
the accelerator pedal is not displaced and any output
driving torque is not produced. When the accelerator pedal
is operated at time tl, a desired driving torque To2
corresponding to an accelerator pedal displacement is
determined. In this state immediately after the start of
the engine 10, air-fuel ratio is unstable. In this region,
I
the motor/generator 17 produces a supplementary torque to
assist the engine 10. The operating condition of the
engine 10 changes to an operating condition in the region P
by time t2, in which air-fuel ratio is stable and the
torque of the engine increases and hence the
motor/generator 17 stops producing the supplementary torque.
In the region P, the motor generator 17 is driven for power
generation by part of the output torque of the engine.
Power generating amount is adjusted by slightly reducing
air-fuel ratio to increase the output torque of the engine.
After air-fuel ratio is adjusted to 30, engine torque is
kept constant and motor torque is produced. An air-fuel
ratio changing control operation is performed at time t4
when the motor torque difference OTm becomes approximately
equal to the engine torque difference ~Te so that the
output driving torque varies smoothly. In the region S,
CA 02326849 2000-10-26
- 44 -
the engine 10 is operated in the homogeneous charge
combustion mode, electric energy generated by the
turbogenerator 7 is supplied to the motor/generator 17 and
the desired driving torque is produced at time t5.
Fig. 22 shows a control procedure in this embodiment.
In block 260, an operating condition of the HEV is
determined on the basis of a set of data including an
accelerator pedal displacement, a brake pedal displacement
I
and a traveling speed, and a desired driving torque is
calculated in block 261. In block 262, an operating mode
is determined on the basis of the desired driving torque
and the traveling speed.
When the operating mode is in the region O, the
amount of electric energy stored in the electric energy
storage device 5 1s checked in block 263. If the electric
energy storage device 5 is sufficiently charged, the engine
operating in the compression ignition mode in block 264
is assisted by a supplementary torque.
In the region P, the~engine 10 is operated in the
compression ignition mode in block 264 to drive the vehicle.
The motor/generator 17 does not produce any driving force.
The amount of electric energy stored in the electric energy
storage device 5 is checked in block 268. If the electric
energy storage device 5 is insufficiently charged, the
electric energy storage device 5 is charged by using the
CA 02326849 2000-10-26
- 45 -
output of the engine in block 270.
In the regions Q and R, the engine 10 is operated in
the stratified charge combustion mode in block 265. In the
region Q, the motor/generator 17 does not produce any
driving force. The amount of electric energy stored in the
electric energy storage device 5 is checked in block 268.
If the electric energy storage device 5 is insufficiently
charged, power is generated by using the output of the
i
engine in block 270 to charge the electric energy storage
device 5. In the region R, power is generated by the
turbogenerator 7 in block 271 and the electric energy
generated by the turbogenerator 7 is used for generating an
supplementary torque by the motor/generator in block 275 to
assist the engine.
In the region S, the engine is operated in the
homogeneous charge combustion mode in block 266. The
turbogenerator 7 generates power in block 272, and the
motor/generator is operated in block 276 by using electric
energy generated by the turbogenerator 7 to produce a
supplementary torque to assist the engine.
Fig. 23 shows a turbogenerator to be employed in the
present invention. The turbogenerator comprises a shaft 83,
a turbine wheel 87 mounted on the shaft 83, a field magnet
rotor 93 mounted on the shaft 83, a radial bearing 80, a
thrust bearing 81, an angular position sensor 90, a shaft
' CA 02326849 2000-10-26
- 46 -
seal 91 and a stator 92. An oil is supplied through an oil
supply port 85 to cool and lubricate the shaft 83, and is
discharged through a discharge port 86. The exhaust gas
discharged from the engine flows into a turbine chamber 82
housing the turbine wheel 87 to drive the turbine wheel 87.
The exhaust gas is discharged through an discharge opening
84.
Fig. 24 shows amount of heat that can be recovered
from the exhaust gas by the turbogenerator employed in the
present invention. Fig. 24 shows the relation between
engine speed and engine torque. In Fig. 24, a curve 94
indicates the output torque characteristic of the engine,
dotted lines 95 to 99 connect points indicating the same
amount of recovered heat, and numerals enclosed by a
rectangle indicates the ratio of the amount of recovered
exhaust heat to that indicated by the dotted line 95. A
greater amount of exhaust heat can be recovered when the
engine torque is higher.
Fig. 25 shows the relation between accelerator pedal
displacement and brake pedal displacement, and driving
torque and regenerative braking torque. Suppose that the
accelerator pedal is depressed while the HEV is traveling
at a low traveling speed V1 to accelerate the HEV for
steady-state traveling at an increased traveling speed V2.
The HEV is in a steady-state traveling at the traveling
CA 02326849 2000-10-26
- 47 -
speed V1 in a state X, and the same is in a steady-state
traveling at the traveling speed V2 in a state Z. When an
accelerator pedal displacement a1 in the state X is
increased to an accelerator pedal displacement a2, the
traveling speed changes scarcely immediately after the
increase of accelerator pedal displacement and the desired.
driving torque is equal to that in a state Y' shown in Fig.
( 25. Since the traveling speed increases gradually, the
desired driving torque is equal to that in the state Y.
Details between the state X and the state Y are mentioned
in connection with the description of the first embodiment
with reference to Figs. 1 to 12.
In the state Y, the traveling speed is V2 and. the
accelerator pedal displacement remains at a2. Consequently,
the traveling speed increases further to V3. The
accelerator pedal displacement must be reduced to maintain
the traveling speed at~V2. If the accelerator pedal
displacement i~ reduced to a3, the traveling speed is
maintained at V2 and the HEV travels in a steady-state
traveling mode in the state Z. A state change A occurs
between the state Y and the state Z. Reduction of
accelerator pedal displacement in the state Z is a
preparatory operation for braking and the HEV operates in
the regenerative braking mode shown in Figs. 11A and 11B.
CA 02326849 2000-10-26
- 48 -
The state change A will be described.
A state change X -~ Y -> Z is illustrated in Figs. 26,
27 and 28. Power sources to be used are shown in Fig. 28.
When the operating state changes from the state Y to the
state Z, the operating state changes from a series/parallel
state changes to a state in which only the engine is used.
Fig. 27 shows a motor operating mode. In the state Y, the
turbogenerator and the generator are used for power
generation, and the motor generator is used for driving.
In the state Z, the motor generator is stopped. Fig. 26
shows an engine operating mode. The engine is operated in
the homogeneous charge combustion mode in the state Y and
in the stratified charge combustion mode in the state Z.
Fig. 29 shows a change from the state Y to the state
Z. In a region C in the state Y, accelerator pedal
displacement is a2, desired driving torque is To2 and
output driving torque is T2. The output driving torque T2
is the sum of an engine torque' Te3 and a motor torque Tml.
When accelerator pedal displacement-is changed from a2 to
a3 to maintain the traveling speed, desired driving torque
becomes To3, and the operating mode of the engine is
changed from the homogeneous charge combustion mode to the
stratified charge combustion mode, in which air-fuel ratio
is changed from 14.7 to about 30. When the operating mode
CA 02326849 2000-10-26
- 49 -
of the engine is changed, engine torque drops by ~Te.
Therefore, a current command is changed to increase motor
torque by ~Tm. Consequently, the operating condition can
be changed from that in the region C to that in region B'
without changing torque stepwise. After the region has
been changed at time tl, air-fuel ratio is maintained at 30
until time t2, and the torque of the motor is reduced
( gradually to naught by the time t2. After the motor torque
has been reduced to naught, air-fuel ratio is changed to 40
to reduce engine torque to an output driving torque T3 by
time t3. Thus, operating region can smoothly be changed.
Since electric power generated by using energy recovered
from the exhaust gas by the turbogenerator is used to
produce the torque increment OTm, the efficiency is not
reduced by the changing control.
INDUSTRIAL APPLICABILITY
The hybrid vehicle driving system according to the
present invention having the means for combining the
respective output torques of the internal-combustion engine
and the motor or transmitting the output torque of the
internal-combustion engine or that of the motor comprises
the turbogenerator for converting the energy of the exhaust
gas of the internal-combustion engine into electric energy,
CA 02326849 2000-10-26
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and the means for electrically connecting the
turbogenerator and the electric motor, the engine of the
HEV can be operated in the lean combustion mode for most
part of its operating time and hence the fuel consumption
rate and efficiency of the engine can be improved.
According to the present invention, a hybrid vehicle
driving method operates an internal-combustion engine
selectively in a first operating mode in which a mixture of
an air-fuel ratio not lower than a predetermined first air-
fuel ratio is supplied to the internal-combustion engine or
a second operating mode in which a mixture of an air-fuel
ratio not higher than a predetermined second air-fuel ratio
lower than the first air-fuel ratio is supplied to the
internal-combustion engine, and drives wheels by a
composite torque produced by combining the. respective
output torques of the internal-combustion engine and an
electric motor, wherein the electric motor is driven and
maintains the air-fuel ratio of the mixture supplied to the
internal-combustion engine at the first air-fuel ratio when
the air-fu$1 ratio decreases below the first air-fuel ratio
while the internal-combustion engine is operating in the
first operating mode. Thus, the present invention provides
a HEV driving system capable of changing its operating
condition in a lean combustion region to that in a
stoichiometric combustion region without operating in an
CA 02326849 2000-10-26
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operating condition that produces NOx and provides an
automobile that does not cause air contamination.
According to the present invention, a second air-
fuel ratio engine torque that may be produced by the
internal-combustion engine when a mixture of the second
air-fuel ratio is supplied to the internal-combustion
engine is estimated, a torque difference between an engine
torque that may be produced when a mixture of the first
f
air-fuel ratio is supplied to the engine and the estimated
second air-fuel ratio engine torque is calculated, and the
operating mode is changed from the first operating mode to
the second operating mode when the output torque of the
electric motor is approximately equal to the calculated
torque difference. Thus, the present invention provides a
driving method that does not change the torque suddenly and
improves the performance of the automobile.
According to the present invention, a hybrid vehicle
comprises an internal-combustion engine capable of
operating in a compression ignition mode, a generator
capable of converting the output energy of the internal-
combustion engine into electric energy, and an electric
motor capable of converting the electric energy generated
by the generator into driving energy for driving driving
wheels. Thus, a torque sufficient for driving a vehicle
can be produced by the engine capable of producing a small
~
CA 02326849 2000-10-26
- 52 -
torque and of operating in the compression ignition mode.
