Description

Drive System and Control Method of the Same

Technical Field

[0001] The present invention relates to a drive system and a

control method of the drive system. More specifically the

invention pertains to a drive system including an internal

combustion engine equipped with an exhaust treatment catalyst

in an exhaust system, as well as to a control method of such

a drive system.

Background Art

[0002] One proposed drive system has an adsorbent that is

arranged in a branch pipe to absorb uncombusted hydrocarbon (HC)

gas (see, for example, Japanese Patent Laying-Open Gazette No.

HlO -153112) . The branch pipe is branched off from an exhaust

pipe of an engine and is again joined to the exhaust pipe. This

prior art drive system utilizes a negative pressure in ari air

intake system to open a valve disposed in the branch pipe on

a start of the engine. In the open position of the valve, the

exhaust gas of the engine is led to the branch pipe and goes

through the adsorbent, which absorbs the uncombusted HC gas

included in the exhaust gas. The HC gas absorbed to the

adsorbent is released with an increase in temperature of the

adsorbent and is led to the air intake system via an EGR pipe

to be burned out .

Disclosure of the Invention

[0003] This prior art drive system may, however, cause unstable

operation of the engine and poor emission on a start of the engine ,

In a stop condition of the engine, the fuel vapor may be

accumulated in the air intake system due to oil-tight leakage

of a fuel injection valve with elapse of time. The amount of

the fuel vapor accumulated in the air intake system is not fixed

but is varied depending upon the time elapsed since a stop of

the engine. This undesirably causes a variation in air-fuel

ratio on or immediately after a restart of the engine with engine

cranking and fuel injection under such conditions. The

variation in air-fuel ratio may lead to unstable operation of

the engine and cause some trouble, for example, a misfire. One

possible measure against this problem increases the amount of

fuel injection on the start of the engine by taking into account

the potential variation in amount of the fuel vapor accumulated

in the air intake system. This, however, undesirably worsens

the emission. As mentioned above, the proposed drive system

utilizes the negative pressure in the air intake system to open

the valve and lead the exhaust gas of the engine to the branch

pipe for absorption of the uncorabusted HC gas in the exhaust

gas to the adsorbent . On a start of the engine with engine

cranking, the valve-open timing may be too late to lead the

exhaust gas to the branch pipe. In this case, the fuel vapor

accumulated in the air intake system does not go through the

branch pipe with the adsorbent but is directly discharged to

the outside air.

[0004] The drive system and the drive system control method of

the invention thus aim to prevent a variation in air-fuel ratio

on or immediately after a start of an internal combustion engine .

The drive system and the drive system control method of the

invention also aim to improve emission on a start of the internal

combustion engine. The drive system and the drive system

control method of the invention further aim to ensure

satisfaction of a power demand even during start control of the

internal combustion engine.

[0005] In order to attain at least part of the above and the

other related objects, the drive system and the drive system

control method of the invention have the configurations

discussed below.

[0006] The present invention is directed to a first drive system

including an internal combustion engine equipped with an

exhaust treatment catalyst in an exhaust system. The first drive

system includes : a fuel exhaust adsorption unit that is arranged

in the exhaust system to absorb a component of a fuel exhaust ;

a cranking structure that cranks the internal combustion

engine; and a start control module that, in response to a start

instruction of the internal combustion engine, controls the

cranking structure to crank the internal combustion engine and

controls the internal combustion engine to start fuel injection

from a fuel injection valve and eventually start the internal

combustion engine after cranking of the internal combustion

engine progresses to a specific extent that is required for

substantial elimination of a fuel vapor accumulated in an air

intake system and in a combustion chamber.

[0007] In response to a start instruction of the internal

combustion engine that is equipped with the exhaust treatment

catalyst and the fuel exhaust adsorption unit in the exhaust

system, the first drive system of the invention controls the

cranking structure to crank the internal combustion engine and

controls the internal combustion engine to start fuel injection

from the fuel injection valve and eventually start the internal

combustion engine after cranking of the internal combustion

engine progresses to the specific extent that is required for

substantial elimination of the fuel vapor accumulated in the

air intake system and in the combustion chamber. The fuel

injection is performed to start the internal combustion engine

after substantial elimination of the fuel vapor accumulated in

the air intake system and in the combustion chamber. This

arrangement effectively prevents a variation in air- fuel ratio

on or immediately after a start of the internal combustion

engine . The fuel exhaust adsorption unit absorbs the component

of the fuel exhaust flowed into the exhaust system in the course

of cranking the internal combustion engine. This arrangement

improves emission on a start of the internal combustion engine.

The first drive system of the invention may be mounted a motor

vehicle as its driving system. One typical application of the

invention is thus a motor vehicle equipped with this first drive

system.

[0008] The present inbention is also directed to a second drive

system including an internal combustion engine equipped with

an exhaust treatment catalyst in an exhaust system. The second

drive system includes: a fuel exhaust adsorption unit that is

arranged in the exhaust system to absorb a component of a fuel

exhaust; a changeover mechanism that is driven by an actuator

to change over a flow path of the fuel exhaust between a first

gas pathway that causes a main portion of the fuel exhaust

introduced into the exhaust system to be discharged without

transmission through the fuel exhaust adsorption unit and a

second gas pathway that causes all the fuel exhaust introduced

into the exhaust system to be discharged after transmission

through the fuel exhaust adsorption unit; a cranking structure

that cranks the internal combustion engine,- and a start control

module that, in response to a start instruction of the internal

combustion engine, drives the actuator and controls the

changeover mechanism to change over the flow path of the fuel

exhaust to the second gas pathway and controls the internal

combustion engine to start cranking the internal combustion

engine and eventually start the internal combustion engine

after the changeover of the flow path of the fuel exhaust to

the second gas pathway by the changeover mechanism.

[0009] In the second drive system of the invention, the

changeover mechanism is driven by the actuator to change over

the flow path of the fuel exhaust between the first gas pathway

that causes the main portion of the fuel exhaust introduced into

the exhaust system to be discharged without transmission

through the fuel exhaust adsorption unit and the second gas

pathway that causes all the fuel exhaust introduced into the

exhaust system to be discharged after transmission through the

fuel exhaust adsorption unit. In response to a start

instruction of the internal combustion engine that is equipped

with the exhaust treatment catalyst and the fuel exhaust

adsorption unit in the exhaust system, the second drive system

of the invention drives the actuator and controls the changeover

mechanism to change over the flow path of the fuel exhaust to

the second gas pathway and controls the internal combustion

engine to start cranking the internal combustion engine and

eventually start the internal combustion engine after the

changeover of the flow path of the fuel exhaust to the second

gas pathway by the changeover mechanism. This arrangement

desirably prevents direct discharge of the fuel vapor, which

is accumulated in the air intake system and is flowed into the

exhaust system in the course of cranking the internal combustion

engine, without transmission through the fuel exhaust

adsorption unit and thus improves the emission on a start of

the internal combustion engine . The second drive system of the

invention may be mounted a motor vehicle as its driving system.

One typical application of the invention is thus a motor vehicle

equipped with this second drive system.

[0010] In one preferable embodiment of the invention, the second

drive system further includes a changeover detection unit that

detects the changeover of the flow path of the fuel exhaust to

the second gas pathway by the changeover mechanism. ^" The start

control module controls the cranking structure to start

cranking the internal combustion engine, in response to

detection of the changeover of the flow path of the fuel exhaust

to the second gas pathway by the changeover detection unit.

This arrangement more effectively prevents direct discharge of

the fuel vapor, which is accumulated in the air intake system

and is flowed into the exhaust system in the course of cranking

the internal combustion engine, without transmission through

the fuel exhaust adsorption unit .

[0011] In one preferable structure of the second drive system

of the invention, the start control module controls the internal

combustion engine to start fuel injection from a fuel injection

valve and eventually start the internal combustion engine after

cranking of the internal combustion engine progresses to a

specific extent that is required for substantial elimination

of a fuel vapor accumulated in an air intake system and in a

combustion chamber. The fuel injection is performed to start

the internal combustion engine after substantial elimination

of the fuel vapor accumulated in the air intake system and in

the combustion chamber. This arrangement effectively prevents

a variation in air-fuel ratio on or immediately after a start

of the internal combustion engine.

[0012] In the first and second drive system of the invention

that controls the internal combustion engine to start fuel

injection from a fuel injection valve and eventually start the

internal combustion engine after cranking of the internal

combustion engine progresses to a specific extent, the start

control module may control the internal combustion engine to

start the fuel injection from the fuel injection valve and start

the internal combustion engine after cranking of the internal

combustion engine continues for a predetermined time period,

which expects the progress of cranking to the specific extent.

[0013] In the first and second drive system of the invention,

the start control module may function in response to a first

start instruction of the internal combustion engine after

system activation.

[0014] In one preferable structure of either of the first drive

^■ system and the second drive system of the invention, the exhaust

treatment catalyst is arranged downstream the fuel exhaust

adsorption unit to convert the component of the fuel exhaust

absorbed by the fuel exhaust adsorption unit and later released

from the fuel exhaust adsorption unit. The component of the

fuel exhaust released from the fuel exhaust adsorption unit is

converted by the active exhaust treatment catalyst.

[0015] In one preferable embodiment of either of the first drive

system and the second drive system of the invention, the drive

system is designed to directly or indirectly use output power

of the internal combustion engine and enable output of power

to a driveshaft and further includes : a driveshaft motor that

outputs power to the driveshaft; an accumulator unit that

receives and transmits electric power from and to the driveshaft

motor; and a power demand setting module that sets a power demand

in response to an operator's manipulation. The start control

module controls the driveshaft motor to output a power

equivalent to the set power demand to the driveshaft. This

arrangement ensures satisfaction of the power demand, although

a relatively long time is required for a start of the internal

combustion engine. In this embodiment, the start control

module may control the driveshaft motor to output the power

equivalent to the set power demand to the driveshaft within an

output limit of the accumulator unit. This arrangement

effectively prevents over discharge of the accumulator unit.

In one preferable application, the drive system of this

embodiment further includes an electric power-mechanical power

input output mechanism that is connected with an output shaft

of the internal combustion engine and with the driveshaft to

function as the cranking structure with input and output of

electric power and mechanical power and to output at least part

of the output power of the internal combustion engine to the

driveshaft after a start of the internal combustion engine . One

typical example of the electric power-mechanical power input

output mechanism includes: a- three shaft-type power input

output module that is linked to three shafts, the output shaft

of the internal combustion engine, the driveshaft, and a third

rotating shaft, and automatically inputs and outputs power from

and to a residual one shaft based on powers input from and output

to any two shafts among the three shafts,- and a rotating shaft

motor that is capable of inputting and outputting power from

and to the third rotating shaft. Another typical example of

the electric power-mechanical power input output mechanism is

a pair-rotor motor that has a first rotor connected to the output

shaft of the internal combustion engine and a second rotor

connected to the driveshaft and is driven to rotate the first

rotor relative to the second rotor through electromagnetic

operations of the first rotor and the second rotor.

[0016] The present invention is directed to a first control

method of a drive system including : an internal combustion

engine equipped with an exhaust treatment catalyst in an exhaust

system; a fuel exhaust adsorption unit that is arranged in the

exhaust system to absorb a component of a fuel exhaust; and a

cranking structure that cranks the internal combustion engine.

In response to a start instruction of the internal combustion

engine the first control method of the drive system (a) controls

the cranking structure to crank the internal combustion engine; ^'

and (b) controls the internal combustion engine to start fuel

injection from a fuel injection valve and eventually start the

internal combustion engine after cranking of the internal

combustion engine progresses to a specific extent that is

required for substantial elimination of a fuel vapor

accumulated in an air intake system and in a combustion chamber.

[0017] In response to a start instruction of the internal

combustion engine that is equipped with the exhaust treatment

catalyst and the fuel exhaust adsorption unit in the exhaust

system, the first control method of the drive system of the

invention controls the cranking structure to crank the internal

combustion engine and controls the internal combustion engine

to start fuel injection from the fuel injection valve and

eventually start the internal combustion engine after cranking

of the internal combustion engine progresses to the specific

extent that is required for substantial elimination of the fuel

vapor accumulated in the air intake system and in the combustion

chamber. The fuel injection is performed to start the internal

combustion engine after substantial elimination of the fuel

vapor accumulated in the air intake system and in the combustion

chamber. This arrangement effectively prevents a variation in

air-fuel ratio on or immediately after a start of the internal

combustion engine. The fuel exhaust adsorption unit absorbs

the component of the fuel exhaust flowed into the exhaust system

in the course of cranking the internal combustion engine. This

arrangement improves emission on a start of the internal

combustion engine.

[0018] The present invention is directed to a second control

method of a drive system including : an internal combustion

engine equipped with an exhaust treatment catalyst in an exhaust

system; a fuel exhaust adsorption unit that is arranged in the

exhaust system to absorb a component of a fuel exhaust; a

changeover mechanism that is driven by an actuator to change

over a flow path of the fuel exhaust between a first gas pathway

that causes a main portion of the fuel exhaust introduced into

the exhaust system to be discharged without transmission

through the fuel exhaust adsorption unit and a second gas

pathway that causes all the fuel exhaust introduced into the

exhaust system to be discharged after transmission through the

fuel exhaust adsorption unit,- and a cranking structure that

cranks the internal combustion engine. In response to a start

instruction of the internal combustion engine, the second

control method of the drive system (a) drives the actuator and

controlling the changeover mechanism to change over the flow

path of the fuel exhaust to the second gas pathway; and (b) controls the internal combustion engine to start cranking the

internal combustion engine and eventually start the internal

combustion engine after the changeover of the flow path of the

fuel exhaust to the second gas pathway by the changeover

mechanism.

[0019] In the second control method of the drive system of the

invention, the changeover mechanism is driven by the actuator

to change over the flow path of the fuel exhaust between the

first gas pathway that causes the main portion of the fuel

exhaust introduced into the exhaust system to be discharged

without transmission through the fuel exhaust adsorption unit

and the second gas pathway that causes all the fuel exhaust

introduced into the exhaust system to be discharged after

transmission through the fuel exhaust adsorption unit. In

response to a start instruction of the internal combustion

engine that is equipped with the exhaust treatment catalyst and

the fuel exhaust adsorption unit in the exhaust system, the

second control method of the drive system of the invention

drives the actuator and controls the changeover mechanism to

change over the flow path of the fuel exhaust to the second gas

pathway and controls the internal combustion engine to start

cranking the internal combustion engine and eventually start

the internal combustion engine after the changeover of the flow

path of the fuel exhaust to the second gas pathway by the

changeover mechanism. This arrangement desirably prevents

direct discharge of the fuel vapor, which is accumulated in the

air intake system and is flowed into the exhaust system in the

course of cranking the internal combustion engine, without

transmission through the fuel exhaust adsorption unit and thus

improves the emission on a start of the internal combustion

engine .

Brief Description of the Drawings

[0020]

Fig. 1 schematically illustrates the configuration of a

hybrid vehicle equipped with a drive system in one embodiment

of the invention;

Fig. 2 schematically shows the structure of an engine

mounted on the hybrid vehicle of the embodiment;

Fig. 3 schematically illustrates the structure of a

second catalytic conversion unit included in the hybrid vehicle

of the embodiment;

Fig. 4 is a flowchart showing a start control routine

executed by a hybrid electronic control unit included in the

hybrid vehicle of the embodiment;

Fig. 5 is a flowchart showing a drive control routine

executed by the hybrid electronic control unit included in the

hybrid vehicle of the embodiment;

Fig. 6 shows a variation in output limit Wout of a battery

against batter temperature Tb;

Fig.7 shows a variation in output limit correction factor

for the output limit Wout against state of charge SOC of the

battery;

Fig. 8 shows one example of a torque demand setting map,-

Fig. 9 is an alignment chart showing torque-rotation

speed dynamics of respective rotational elements included in

a power distribution integration mechanism in the hybrid

vehicle of the embodiment; and

Fig. 10 schematically illustrates the configuration of

another hybrid vehicle as one modified example.

Best Modes of Carrying Out the Invention

[0021] One mode of carrying out the invention is described below

as a preferred embodiment with reference to the accompanied

drawings. Fig. 1 schematically illustrates the configuration

of a hybrid vehicle 20 equipped with a drive system in one

embodiment of the invention. Fig. 2 schematically shows the

structure of an engine 22 mounted on the hybrid vehicle 20 of

the embodiment. As illustrated in Fig. 1, the hybrid vehicle

20 of the embodiment includes the engine 22, a three shaft-type

power distribution integration mechanism 30 that is linked to

a crankshaft 26 or an output shaft of the engine 22 via a damper

28, a motor MGl that is connected to the power distribution

integration mechanism 30 and has power generation capability,

a reduction gear 35 that is attached to a ring gear shaft 32a

or a driveshaft linked with the power distribution integration

mechanism 30, a motor MG2 that is connected to the reduction

gear 35, and a hybrid electronic control unit 70 that controls

the operations of the whole drive system in the hybrid vehicle

20.

[0022] The engine 22 is an internal combustion engine that

consumes a hydrocarbon fuel, such as gasoline or light oil, to

output power. As shown in Fig. 2, the air cleaned by an air

cleaner 122 and taken in via a throttle valve 124 is mixed with

the atomized gasoline injected by an injector 126 to the

air- fuel mixture. The air-fuel mixture is introduced into a

combustion chamber via an intake valve 128. The introduced

air-fuel mixture is ignited with spark made by a spark plug 130

to be explosively combusted. The reciprocating motions of a

piston 132 by the combustion energy are converted into

rotational motions of the crankshaft 26. The exhaust from the

engine 22 sequentially goes through a first catalytic

conversion unit 134 (filled with three-way catalyst) and a

second catalytic conversion unit 140 to convert toxic

components included in the exhaust, that is, carbon monoxide

(CO) , hydrocarbons (HC) , and nitrogen oxides (NOx) , into

harmless components , and is discharged to the outside air . Fig .

3 schematically illustrates the structure of the second

catalytic conversion unit 140.

[0023] As illustrated in Fig.3, the second catalytic conversion

unit 140 includes a cylindrical inner case 142 filled with a

three-way catalyst 141, a cylindrical outer case 144 having a

larger diameter than the diameter of the inner case 142, a

cylindrical partition member 145 having an opening 145a and

forming a bypass pathway 145b, an HC adsorbent 146 packed in

a ring-shaped space formed in the bypass pathway 145b by an outer

wall of the partition member 145 and an inner wall of the outer

case 144, an exhaust flow changeover valve 147 attached to the

opening 145a of the partition member 145, and an actuator 148

driven to open and close the exhaust flow changeover valve 147.

The actuator 148 is, for example, an electric actuator. An

outer wall of the smaller-diameter inner case 142 and an inner

wall of the larger-diameter outer case 144 define a ring-shaped

space. The ^" inner case 142 and the outer case 144 are arranged,

such that an inlet 142a of the inner case 142 is aligned with

an inlet 144a of the outer case 144 across some space. The

opening 145a of the partition member 145 connects the inlet 142a

of the inner case 142 to the inlet 144a of the outer case 144.

The partition member 145 is designed to have a diameter larger

than the diameter of the inner case 142 but smaller than the

diameter of the outer case 144. The partition member 145 parts

the ring-shaped space defined by the outer wall of the inner

case 142 and the inner wall of the outer case 144 to form the

bypass pathway 145b. The bypass pathway 145b does not directly

lead a gas flow introduced through the inlet 144a of the outer

case 144 to the inlet 142a of the inner case 142 but bypasses

the gas flow. In a closed position of the exhaust flow

changeover valve 147, a gas flow introduced via the inlet 144a

of the outer case 144 into the second catalytic conversion unit

140 is lead through the bypass conduit 145b including the HC

adsorbent 146 to the inlet 142a of the inner case 142. The gas

flow then goes through the three-way catalyst 141 and is flowed

out of the second catalytic conversion unit 140 via an outlet

142b of the inner case 142. In an open position of the exhaust

flow changeover valve 147, on the other hand, a main portion

of the gas flow introduced via the inlet 144a of the outer case

144 into the second catalytic conversion unit 140 ^' is directly

led to the inlet 142a of the inner case 142 via the open exhaust

flow changeover valve 147, while a residual portion of the gas

flow goes through the bypass pathway 145b to the inlet 142a of

the inner case 142. The gas flow then goes through the three-way

catalyst 141 and is flowed out of the second catalytic

conversion unit 140 via the outlet 142b of the inner case 142.

The three-way catalyst 141 mainly consists of an oxidation

catalyst, such as platinum (Pt) or palladium (Pd), a reduction

catalyst, such as rhodium (Rh) , and an assisting catalyst, such

as ceria (CeO ₂ ) . The three-way catalyst 141 is active at high

temperatures. The functions of the oxidation catalyst convert

CO and HC included in the exhaust into water (H ₂ O) and carbon

dioxide (CO ₂ ) . The functions of the reduction catalyst convert

NOx included in the exhaust into nitrogen (N ₂ ) and oxygen (O ₂ ) .

The HC adsorbent 146 mainly composed of zeolite absorbs HC at

low temperatures and releases the absorbed HC at high

temperatures. In a low temperature range where the three-way

catalyst 141 is inactive, setting the exhaust flow changeover

valve 147 to the closed position enables HC to be temporarily

absorbed by the HC adsorbent 146. With a temperature rise, the

three-way catalyst 141 is activated to convert the HC absorbed

by the HC adsorbent 146.

[0024] The engine 22 is under control of an engine ^' electronic

control unit 24 (hereafter referred to as engine ECU 24) . The

engine ECU 24 receives, via its input port (not shown) , signals

from various sensors that measure and detect the conditions of

the engine 22. The signals input into the engine ECU 24 include

a crank position from a crank position sensor 150 measured as

the rotational position of the crankshaft 26, a cooling water

temperature from a water temperature sensor 152 measured as the

temperature of cooling water for the engine 22, a cam position

from a cam position sensor 154 measured as the rotational

position of a camshaft driven to open and close the intake valve

128 and an exhaust valve for gas intake and exhaust into and

from the combustion chamber, a throttle valve position from a

throttle valve position sensor 156 detected as the opening of

the throttle valve 124 , an intake negative pressure or an amount

of intake air from a vacuum sensor 158 measured as the load of

the engine 22, and a valve-closing switch signal from a

valve-closing switch 149 detecting the setting of the -exhaust

flow changeover valve 147 in the closed position. The engine

ECU 24 outputs, via its output port (not shown) , diverse control

signals and driving signals to drive and control the engine 22,

for example, driving signals to the fuel injection valve 126,

driving signals to a throttle motor 136 for regulating the

position of the throttle valve 124, control signals to an

ignition coil 138 integrated with an igniter, control signals

to a variable valve timing mechanism 160 to vary the open and

close timings of the intake valve 128, and driving signals to

the actuator 148 for opening and closing the exhaust flow

changeover valve 147. The engine ECU 24 communicates with the

hybrid electronic control unit 70. The engine ECU 24 receives

control signals from the hybrid electronic control unit 70 to

drive and control the engine 22 , while outputting data regarding

the driving conditions of the engine 22 to the hybrid electronic

control unit 70 according to the requirements.

[0025] The power distribution and integration mechanism 30 has

a sun gear 31 that is an external gear, a ring gear 32 that is

an internal gear and is arranged concentrically with the sun

gear 31, multiple pinion gears 33 that engage with the sun gear

31 and with the ring gear 32, and a carrier 34 that holds the

multiple pinion gears 33 in such a manner as to allow free

revolution thereof and free rotation thereof on the respective

axes. Namely the power distribution and integration mechanism

30 is constructed as a planetary gear mechanism that allows for

differential motions of the sun gear 31, the ring gear 32, and

the carrier 34 as rotational elements. The carrier 34, the sun

gear 31, and the ring gear 32 in the power distribution and

integration mechanism 30 are respectively coupled with the

crankshaft 26 of the engine 22, the motor MGl, and the reduction

gear 35 via ring gear shaft 32a. While the motor MGl functions

as a generator, the power output from the engine 22 and input

through the carrier 34 is distributed into the sun gear 31 and

the ring gear 32 according to the gear ratio. While the motor

MGl functions as a motor, on the other hand, the power output

from the engine 22 and input through the carrier 34 is combined

with the power output from the motor MGl and input through the

sun gear 31 and the composite power is output to the ring gear

32. The power output to the ring gear 32 is thus finally-

transmitted to the driving wheels 63a and 63b via the gear

mechanism 60, and the differential gear 62 from ring gear shaft

32a.

[0026] Both the motors MGl and MG2 are known synchronous motor

generators that are driven as a generator and as a motor. The

motors MGl and MG2 transmit electric power to and from a battery

50 via inverters 41 and 42. Power lines 54 that connect the

inverters 41 and 42 with the battery 50 are constructed as a

positive electrode bus line and a negative electrode bus line

shared by the inverters 41 and 42. This arrangement enables

the electric power generated by one of the motors MGl and MG2

to be consumed by the other motor. The battery 50 is charged

with a surplus of the electric power generated by the motor MGl

or MG2 and is discharged to supplement an insufficiency of the

electric power. When the power balance is attained between the

motors MGl and MG2 , the battery 50 is neither charged nor

discharged. Operations of both the motors MGl and MG2 are

controlled by a motor electronic control unit (hereafter

referred to as motor ECU) 40. The motor ECU 40 receives diverse

signals required for controlling the operations of the motors

MGl and MG2 , for example, signals from rotational position

detection sensors 43 and 44 that detect the rotational positions

of rotors in the motors MGl and MG2 and phase currents applied

to the motors MGl and MG2 and measured by current sensors (not

shown) . The motor ECU 40 outputs switching control signals to

the inverters 41 and 42. The motor ECU 40 communicates with

the hybrid electronic control unit 70 to control operations of

the motors MGl and MG2 in response to control signals

transmitted from the hybrid electronic control unit 70 while

outputting data relating to the operating conditions of the

motors MGl and MG2 to the hybrid electronic control unit 70

according to the requirements.

[0027] The battery 50 is under control of a battery electronic

control unit (hereafter referred to as battery ECU) 52. The

battery ECU 52 receives diverse signals required for control

of the battery 50, for example, an inter-termiήal voltage

measured by a voltage sensor (not shown) disposed between

terminals of the battery 50, a charge-discharge current

measured by a current sensor (not shown) attached to the power

line 54 connected with the output terminal of the battery 50,

and a battery temperature Tb measured by a temperature sensor

51 attached to the battery 50. The battery ECU 52 outputs data

relating to the state of the battery 50 to the hybrid electronic

control unit 70 via communication according to the requirements.

The battery ECU 52 calculates a state of charge (SOC) of the

^■ battery 50, based on the accumulated charge-discharge current

measured by the current sensor, for control of the battery 50.

[0028] The hybrid electronic control unit 70 is constructed as

a microprocessor including a CPU 72, a ROM 74 that stores

processing programs, a RAM 76 that temporarily stores data, and

a non-illustrated input-output port, and a non-illustrated

communication port. The hybrid electronic control unit 70

receives various inputs via the input port : an ignition signal

from an ignition switch 80, a gearshift position SP 'from a

gearshift position sensor 82 that detects the current position

of a gearshift lever 81, an accelerator opening Ace from an

accelerator pedal position sensor 84 that measures a step-on

amount of an accelerator pedal 83, a brake pedal position BP

from a brake pedal position sensor 86 that measures a step-on

amount of a brake pedal 85, and a vehicle speed V from a vehicle

speed sensor 88. The hybrid electronic control unit 70

communicates with the engine ECU 24, the motor ECU 40, and the

battery ECU 52 via the communication port to transmit diverse

control signals and data to and from the engine ECU 24 , the motor

ECU 40, and the battery ECU 52, as mentioned previously.

[0029] The hybrid vehicle 20 of the embodiment thus constructed

calculates a torque demand to be output to the ring gear shaft

32a functioning as the drive shaft, based on observed values

of a vehicle speed V and an accelerator opening Ace, which

corresponds to a driver ' s step-on amount of an accelerator pedal

83. The engine 22 and the motors MGl and MG2 are subjected to

operation control to output a required level of power

corresponding to £he calculated torque demand to the ring gear

shaft 32a . The operation control of the engine 22 and the motors

MGl and MG2 selectively effectuates one of a torque conversion

drive mode, a charge-discharge drive mode, and a motor drive

mode . The torque conversion drive mode controls the operations

of the engine 22 to output a quantity of power equivalent to

the required level of power, while driving and controlling the

motors MGl and MG2 to cause all the power output from the engine

22 to be subjected to torque conversion by means of the power

distribution integration mechanism 30 and the motors MGl and

MG2 and output to the ring gear shaft 32a. The charge-discharge

drive mode controls the operations of the engine 22 to output

a quantity of power equivalent to the sum of the required level

of power and a quantity of electric power consumed by charging

the battery _. 50 or supplied by discharging the battery 50, while

driving and controlling the motors MGl and MG2 to cause all or

part of the power output from the engine 22 equivalent to the

required level of power to be subjected to torque conversion

by means of the power distribution integration mechanism 30 and

the motors MGl and MG2 and output to the ring gear shaft 32a,

simultaneously with charge or discharge of the battery 50. The

motor drive mode stops the operations of the engine 22 and drives

and controls the motor MG2 to output a quantity of power

equivalent to the required level of power to the ring gear shaft

32a. The torque conversion drive mode is equivalent to the

charge-discharge drive mode under the condition of the

charge-discharge power of the battery 50 equal to 0. Namely

the torque conversion drive mode is regarded as one type of the

charge-discharge drive mode. The hybrid vehicle 20 of the

embodiment is accordingly driven with a switchover of the drive

mode between the motor drive mode and the charge-discharge drive

mode .

[0030] The ^" description regards the operations of the hybrid

vehicle 20 of the embodiment having the configuration discussed

above, especially a series of start control for a first start

of the engine 22 after system activation. Fig. 4 is a flowchart

showing a start control routine executed by the hybrid

electronic control unit 70. This start control routine is

triggered by a first start instruction of the engine 22 after

system activation.

[0031] In the start control routine of Fig. 4, the CPU 72 of

the hybrid electronic control unit 70 first gives a

valve-closing instruction to the engine ECU 24 to close the

exhaust flow changeover valve 147 (step SlOO) . The engine ECU

24 receives the valve-closing instruction and actuates and

controls the actuator 148 to close the exhaust flow changeover

valve 147. The CPU 72 inputs a valve-closing switch signal

(step SIlO) and confirms the setting of the exhaust flow

changeover valve 147 in the closed position (step S120) . The

valve-closing switch signal output from the valve-closing

switch 149 is received from the engine ECU 24 by communication.

After confirmation of the closed position of the exhaust flow

changeover valve 147, the CPU 72 sets a value '1' to a flag F

to start cranking the engine 22 according to a drive control

routine described later (step S130) .

[0032] The CPU 72 waits until elapse of a preset time period

since the start of cranking the engine 22 (step S140) and inputs

a rotation speed Ne of the engine 22 (step S150) . When the input

rotation speed Ne of the engine 22 reaches or exceeds a preset

reference rotation speed Nref (step S160) , the CPU 72 gives a

start instruction to the engine ECU 24 to perform fuel injection

control and ignition control (step S170) . The fuel injection

from the fuel injection valve 126 starts after elapse of the

preset time period for cranking the engine 22, because of the

following reason. In a stop condition of the engine 22, the

fuel vapor may be accumulated in an air intake system due to

oil-tight leakage of the fuel injection valve 126 with elapse

of time. The accumulated fuel vapor undesirably causes a

variation in air- fuel ratio on or immediately after a restart

of the engine 22, even when the fuel injection from the fuel

injection valve 126 is regulated to attain a target air-fuel

ratio. This variation in air-fuel ratio may lead to some

trouble, for example, a misfire. The preset time period is

accordingly specified as an engine cranking time required for

substantial elimination of the fuel vapor accumulated in the

air intake system and is set equal to 5 seconds in this

embodiment .

[0033] The CPU 72 subsequently specifies whether the start of

the engine 22 is complete or incomplete (step SlffO) . In the

case of the complete start of the engine 22, the CPU 72 waits

until complete warm-up of the first catalytic conversion unit

134 (filled with the three-way catalyst) and the three-way

catalyst 141 included in the second catalytic conversion unit

140 (step S190) and gives a valve-opening instruction to the

engine ECU 24 to open the exhaust flow changeover valve 147 (step

S200) . The start control routine is then terminated. The HC

included in the exhaust is converted by the catalytic functions

of the three-way catalyst in the first catalytic conversion unit

134 and the three-way catalyst 141 in the second catalytic

conversion unit 140. The HC absorbed by the HC adsorbent 146

is released at high temperatures and is introduced into the

three-way catalyst 141 for catalytic conversion.

[0034] The description regards drive control of the engine 22

and the motors MGl and MG2 at a start of the engine 22. Fig.

5 is a flowchart showing a drive control routine executed by

the hybrid electronic control unit 70. This drive control

routine is triggered by system activation. The drive control

routine of Fig. 5 is thus executed in parallel with the start

control routine of Fig.4 on a first start of the engine 22 after

system activation.

[0035] In the drive control routine of Fig. 5, the CPU 72 of

the hybrid electronic control unit 70 first inputs required data

for control, that is, the accelerator opening Ace from the

accelerator pedal position sensor 84, the vehicle speed V from

the vehicle speed sensor 88, rotation speeds NmI and Nm2 of the

motors MGl and MG2 , and an output limit Wout of the battery 50

(step S210) . The rotation speeds NmI and Nm2 of the motors MGl

and MG2 are computed from the rotational positions of the

respective rotors in the motors MGl and MG2 detected by the

rotational position detection sensors 43 and 44 and are received

from the motor ECU 40 by communication. The output limit Wout

of the battery 50 is set corresponding to the battery

temperature Tb of the battery 50 measured by the temperature

sensor 51 and the state of charge SOC of the battery 50 and is

received from the battery ECU 52 by communication. A concrete

procedure of setting the output limit Wout of the battery 50

specifies a base value of the output limit Wout corresponding

to the measured battery temperature Tb, specifies an output

limit correction factor corresponding to the state of charge

SOC of the battery 50, and multiplies the specified base value

of the output limit Wout by the specified output limit

correction factor to determine the output limit Wout of the

battery 50. Fig. 6 shows a variation in output limit Wout of

the battery 50 against the battery temperature Tb. Fig. 7 shows

a variation" in output limit correction factor for ^' the output

limit Wout against the state of charge SOC of the battery 50.

[0036] After the data input, the CPU 72 sets a torque demand

Tr* to be output to the ring gear shaft 32a or the driveshaft

linked with the drive wheels 63a and 63b as a required torque

for the hybrid vehicle 20, based on the input accelerator

opening Ace and the input vehicle speed V (step S220) . A

concrete procedure of setting the torque demand Tr* in this

embodiment stores in advance variations in torque demand Tr*

against the accelerator opening Ace and the vehicle speed V as

a torque demand setting map in the ROM 74 and reads the torque

demand Tr* corresponding to the given accelerator opening Ace

and the given vehicle speed V from this torque demand setting

map. One example of the torque demand setting map is shown in

Fig. 8. [0037] The CPU 72 subsequently identifies the value of the flag

F representing a start of cranking the engine 22 (step S230) .

When the flag F is equal to 0 , a value '0' is set to a torque

command TmI* as a torque to be output from the motor MGl (step

S240) . When the flag F is equal to 1, on the other hand, a

cranking torque Tcr required for cranking the engine 22 is set

to the torque command TmI* of the motor MGl (step S250) . Fig.

9 is an alignment chart showing torque-rotation speed dynamics

of the respective rotational elements included in the power

distribution integration mechanism 30. The left axis 'S ¹

represents a rotation speed of the sun gear 31 that is equivalent

to the rotation speed NmI of the motor MGl. The middle axis

¹ C represents a rotation speed of the carrier 34 that is

equivalent to the rotation speed Ne of the engine 22. The right

axis ¹ R ¹ represents a rotation speed Nr of the ring gear 32 that

is equivalent to division of the rotation speed Nm2 of the motor

MG2 by a gear ratio Gr of the reduction gear 35. Output of an

upward torque on the axis ' S ' from the motor MGl cranks the engine

22. Two thick arrows on the axis 'R' represent a torque

(-Tml*/p) applied to the ring gear shaft 32a by output of the

torque TmI* from the motor MGl and a torque (Tm2*-Gr) applied to the ring gear shaft 32a via the reduction gear 35 by output

of a torque Tm2* from the motor MG2.

[0038] After setting the torque command TmI* of the motor MGl,

the CPU 72 calculates an upper torque restriction Tmax as a

maximum possible torque output from the motor MG2 according to

Equation (1) given below (step S260) . The calculation

subtracts the product of the torque command TmI* and the current

rotation speed NmI of the motor MGl, which represents the power

consumption (power generation) of the motor MGl, from the output

limit Wout of the battery 50 and divides the difference by the

current rotation speed Nm2 of the motor MG2 :

Tmax = (Wout - TmI*-NmI) / Nm2 (1)

The CPU 72 then calculates a tentative motor torque Tm2tmp as

a torque to be output from the motor MG2 from the torque demand

Tr*, the torque command TmI* of the motor MGl, a gear ratio p of the power distribution integration mechanism 30, and the gear

ratio Gr of the reduction gear 35 according to Equation (2) given

below (step S270) :

Tm2tmp = (Tr*+Tml*/p) / Gr (2)

The CPU 72 compares the calculated upper torque restriction Tmax

with the calculated tentative motor torque Tm2tmp and sets the

smaller to a torque command Tm2* of the motor MG2 (step S280) .

Such setting of the torque command Tm2* of the motor MG2

restricts the torque demand Tr* to be output to the ring gear

shaft 32a or the driveshaft within the range of the output limit

Wout of the battery 50. Equation (2) is readily led from the

alignment chart of Fig. 9.

[0039] After setting the torque commands TmI* and Tm2* of the

motors MGl and MG2 in the above manner, the CPU 72 sends the

torque commands TmI* and Tm2* to the motor ECU 40 (Step S290) .

The motor ECU 40 receives the torque commands TmI* and Tm2* and

performs switching control of the switching elements included

in the respective inverters 41 and 42 to drive the motor MGl

with the torque command TmI* and the motor MG2 with the torque

command Tm2*.

[0040] The processing of steps S210 to S290 is repeated until

completion of the start of the engine 22 (step S300) by execution

of the start control routine of Fig. 4. After completion of

the start of the engine 22 (step S300) , the CPU 72 changes over

the drive mode of the hybrid vehicle 20 from the motor drive

mode to the charge-discharge drive mode (step S310) and exits

from this drive control routine. As described previously, the

start control routine of Fig. 4 starts the fuel injection

control and the ignition control after elapse of the preset time

period (for example, 5 seconds) for cranking the engine 22. A

relatively long time is thus required for a complete start of

the engine 22. On the complete start of the engine 22, the

torque demand Tr* is output to the ring gear shaft 32a or the

driveshaft .

[0041] As described above, at the time of a first start of the

engine 22 after system activation, the hybrid vehicle 20 of the

embodiment starts fuel injection from the fuel injection valve

126 to start the engine 22 after cranking the engine 22 for the

preset time period. Such control ensures start of fuel

injection from the fuel injection valve 126 after substantial

elimination of the fuel vapor accumulated in the air intake

system. This effectively prevents a variation of the air-fuel

ratio and stabilizes the drive of the hybrid vehicle 20 on or

immediately after a start of the engine 22. The motor MG2 is

driven and controlled to output the torque demand Tr* to the

ring gear shaft 32a or the driveshaft . The drive control of

this embodiment satisfies output of the torque demand Tr* to

the ring gear shaft 32a, although requiring a relatively long

time for a complete start of the engine 22.

[0042] The hybrid vehicle 20 of the embodiment starts cranking

the engine 22 after closing the exhaust flow changeover valve

147. Such control enables the fuel vapor accumulated in the

air intake system to be effectively absorbed by the HC adsorbent

146. This improves the emission on the start of the engine 22.

The closed position of the exhaust flow changeover valve 147

is confirmed by the valve-closing switch signal output from the

valve-closing switch 149. This further ensures effective

absorption of the fuel vapor accumulated in the air intake

system to the HC adsorbent 146.

[0043] The hybrid vehicle 20 of the embodiment starts cranking

the engine ^' 22 after confirming the closed position of the

exhaust flow changeover valve 147 based on the valve-closing

switch signal output from the valve-closing ¹ switch 149. This

method is, however, not restrictive but any other suitable

technique may be applied to confirm the closed position of the

exhaust flow changeover valve 147. One applicable technique

measures the electric current applied to the electric actuator

148 for confirmation of the closed position of the exhaust flow

changeover valve 147. A modified flow of the start control may

not directly confirm the closed position of the exhaust flow

changeover valve 147 but may start cranking the engine 22 after

elapse of a preset time period since output of a valve-closing

instruction. When a distance between the air intake system and

the HC adsorbent 146 is in a specified range, the start control

may immediately start cranking the engine 22 without confirming

the closed position of the exhaust flow changeover valve 147.

[0044] In the hybrid vehicle 20 of the embodiment, the second

catalytic conversion unit 140 is designed to introduce the HC,

which is absorbed by the HC adsorbent 146 and is later released

from the HC adsorbent 146, into the three-way catalyst 141 for

catalytic conversion. The HC absorbed by the HC adsorbent 146

and later released from the HC adsorbent 146 may directly be

led to the air intake system via an EGR pipe to be burned out .

[0045] The "hybrid vehicle 20 of the embodiment includes two

catalytic conversion units, that is, the first catalytic

conversion unit 134 and the second catalytic conversion unit

140. The hybrid vehicle may, however, have only one catalytic

conversion unit, that is, the second catalytic conversion unit

140, or may have three or more catalytic conversion units.

[0046] In the hybrid vehicle 20 of the embodiment, the power

of the engine 22 is output via the power distribution

integration mechanism 30 to the ring gear shaft 32a or the

driveshaft connected to the drive wheels 63a and 63b. The

technique of the invention is, however, not restricted to this

configuration but may also be applicable to a hybrid vehicle

220 of a modified configuration shown in Fig. 10. The hybrid

vehicle 220 of Fig. 10 has a pair-rotor motor 230 including an

inner rotor 232 connected to the crankshaft 26 of the engine

22 and an outer rotor 234 connected to a driveshaft for output

of power to the drive wheels 63a and 63b. The pair-rotor motor

230 transmits part of the output power of the engine 22 to the

driveshaft, while converting the residual engine output power

into electric power.

[0047] The technique of the invention is applicable to the hybrid

vehicle of any other structure including: an engine equipped

with an HC adsorbent and an exhaust treatment catalyst for

catalytic conversion in an exhaust system; and a cranking device

for cranking the engine. The technique of the invention is not

restricted to the hybrid vehicles but is also applicable to

conventional motor vehicles without a drive motor, as well as

drive systems that are not mounted on the motor vehicles .

[0048] The embodiment discussed above is to be considered in

all aspects as illustrative and not restrictive. There maybe

many modifications, changes, and alterations without departing

from the scope or spirit of the main characteristics of the

present invention.

Industrial Applicability

The technique of the present invention is preferably

applicable to the manufacturing industries of drive systems and

automobiles .