Direct injection type internal combustion engine control apparatus and control method of the same

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2000-136046 filed on May 9, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control apparatus and a control method of a direct injection type internal combustion engine in which fuel delivered from a fuel pump is directly injected into a combustion chamber from a fuel injection valve and the thus-formed mixture is ignited by an ignition plug. In particular, the invention relates to a direct injection type internal combustion engine control apparatus that automatically stops a direct injection type internal combustion engine if during operation of the internal combustion engine, the operating state of the engine meets an automatic stop condition, and that automatically starts operation of the engine if an automatic start condition is met.

2. Description of Related Art

A conventional direct injection type internal combustion engine is known which realizes lean burn when the engine is in a low load state, for example, during idling or the like, and thereby achieves both high output and reduced fuel consumption and also reduces emissions of carbon dioxide and the like (Japanese Patent Application Laid-Open No. 10-299543). In order to ensure that the mixture will be ignited without fail during lean burn, such a direct injection type internal combustion engine performs stratified charge combustion in which fuel is injected during the compression stroke to provide a fuel-rich mixture stratified around the ignition plug before being ignited to burn. In a case where the combustion is to be performed at a stoichiometric air-fuel ratio, the engine performs uniform combustion in which fuel is injected during the intake stroke to produce a state in which fuel is uniformly dispersed in the entire combustion chamber before being burned.

An automatic stop/start apparatus for an automotive internal combustion engine, that is, a generally-termed economy running system, is known which, for the purpose of improving fuel economy or the like, automatically stops the internal combustion engine at the time of a stop of the motor vehicle at an intersection or the like, and then automatically starts the engine by turning the starter upon an operation for starting the vehicle so that the vehicle can be pulled off (Japanese Patent Application Laid-Open No. HEI 10-47104).

Therefore, by combining this automatic stop/start apparatus with the above-described direct injection type internal combustion engine, a further fuel economy improvement can be expected.

For fuel injection during the compression stroke of a direct injection type internal combustion engine, fuel needs to be injected into a high-pressure combustion chamber. Therefore, a typical direct injection type internal combustion engine employs a high-pressure fuel pump to highly pressurize fuel and deliver high-pressure fuel toward the fuel injection valve side.

However, when such a direct injection type internal combustion engine is automatically stopped by the automatic stop/start apparatus, the high-pressure fuel pump also stops. Therefore, during the automatic stop, high-pressure fuel is not supplied to the fuel injection valve side. Even though the fuel injection valve side, including the fuel piping, is tightly closed, fuel gradually leaks. Therefore, during the automatic stop, the accumulated fuel pressure drops.

After that, at the time of an automatic start, the driving of the fuel pump is started. However, if the fuel pressure is insufficient for the compression-stroke fuel injection due to a fuel pressure decrease occurring during the automatic stop, it is inevitable to perform uniform combustion in which fuel is injected during the intake stroke during which good injection is possible even at low fuel injection pressure, until a sufficient fuel pressure is recovered. Therefore, even if the operating state of the engine other than the fuel pressure allows stratified charge combustion upon automatic start, the uniform combustion must be performed. Hence, the improvement in fuel economy and the like may become insufficient.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a direct injection type internal combustion engine control apparatus capable of maintaining a sufficient fuel pressure for the compression-stroke fuel injection for a long time even after the internal combustion engine has been stopped by an automatic stop function, and capable of increasing the frequency of performing the compression-stroke injection after the engine is automatically started. Operation and advantages obtained by the invention will be described.

A control apparatus of. a direct injection type internal combustion engine in which an air-fuel mixture formed by injecting a fuel delivered from a fuel pump, directly from a fuel injection valve into a combustion chamber, is ignited by an ignition plug, the control apparatus is provided with an automatic stop permitting unit that permits an automatic stop of the internal combustion engine if during an operation of the internal combustion engine, an operating state of the internal combustion engine meets an automatic stop condition, an automatic start permitting unit that permits an automatic start of the internal combustion engine if the operating state of the internal combustion engine meets an automatic start condition, and a fuel pressure raising unit that raises a fuel pressure on a fuel injection valve side during a first period of time_prior to the automatic stop permitted by the automatic stop permitting unit.

The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side immediately prior. to the automatic stop. Therefore, after the delivery of high-pressure fuel from the fuel pump stops upon the automatic stop of the direct injection type internal combustion engine, the fuel pressure starts to gradually decrease from a higher fuel pressure, in comparison with the conventional art in which the engine is stopped with an ordinary fuel pressure state. As a result, a long time of engine stop is allowed before the fuel pressure decreases to a pressure that makes it impossible to perform appropriate fuel injection into the combustion chamber during the compression stroke.

Therefore, the possibility that a fuel pressure sufficient for the compression-stroke fuel injection will be maintained immediately after a subsequent automatic start is increased. If such a fuel pressure is maintained, the stratified charge combustion can be accomplished by performing the compression-stroke injection immediately after the subsequent automatic start provided that the internal combustion engine is in an operating state that allows the stratified charge combustion. Thus, the frequency of performing the compression-stroke injection following an automatic start can be increased, and sufficient improvements in fuel economy and the like can be achieved.

The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side during the first period of time prior to the automatic stop by adjusting an amount of the fuel delivered from the fuel pump to a maximum.

Thus, by maximizing the amount of delivery from the fuel pump, the fuel pressure can be quickly brought to a sufficiently high pressure state. As a result, the frequency of performing the compression-stroke injection following an automatic start is further increased, and a fuel economy improvement and the like will become more effective.

The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. During the first period of time prior to the automatic stop, the fuel pressure raising unit raises the fuel pressure on the fuel injection valve side so as to temporarily open the relief valve by adjusting the amount of the fuel delivered from the fuel. pump to the maximum.

During the pressure raise continuation duration immediately prior to the automatic stop, the fuel pressure raising unit raises the fuel pressure by adjusting the amount of delivery from the fuel pump to the maximum, so that the relief valve is temporarily opened. This may open the relief valve, which is hardly ever opened during normal operation.

Therefore, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the locking or fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.

Furthermore, by setting a long pressure raise continuation duration so as to deliver a large amount of high-pressure fuel toward the fuel injection valve side and to discharge fuel via the relief valve, a reduced fuel temperature on the fuel injection valve side can be achieved immediately prior to the automatic stop. Therefore, it is possible to maintain a sufficiently high fuel pressure achieved by thermal expansion caused by increases in the fuel temperature during the automatic stop of the engine. Consequently, the frequency of performing the compression-stroke injection following an automatic stop can be further increased, and improvements in fuel economy and the like can be more effectively achieved.

The control apparatus is further provided with a fuel pressure control unit that adjusts the fuel pressure on the fuel injection valve side to a target fuel pressure that is set in accordance with the operating state of the internal combustion engine by adjusting an amount of the fuel delivered from the fuel pump. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side prior to the automatic stop by correcting the target fuel pressure to a higher level.

If the fuel pressure control unit adjusts the fuel pressure to a target fuel pressure in accordance with the operating state of the internal combustion engine by adjusting the amount of delivery from the fuel pump, the fuel pressure raising unit is able to raise the fuel pressure by correcting the target fuel pressure set by the fuel pressure control unit in accordance with the operating state of the internal combustion engine to an increase side immediately prior to the automatic stop.

Therefore, immediately prior to the automatic stop, the control apparatus realizes a high fuel pressure that is higher than a usual fuel pressure adjusted by the fuel pressure control unit. As a result, a longer-than-usual time of engine stop is allowed before the fuel pressure decreases to a pressure that makes it impossible to perform fuel injection into the combustion engine during the compression-stroke injection.

Therefore, the possibility of performance of the compression-stroke injection immediately following a subsequent automatic start is increased, and the frequency of performing the compression-stroke injection is increased. Thus, sufficient improvements in fuel economy and the like can be achieved.

The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side to at least the predetermined valve opening pressure of the relief valve prior to the automatic stop.

The fuel pressure raising unit raises the fuel pressure to at least the predetermined valve opening pressure of the relief valve provided on the fuel injection valve side, immediately prior to the automatic stop. This provides an occasion of opening the relief valve, which is hardly ever opened during normal operation.

Therefore, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.

The internal combustion engine includes a relief valve that opens and discharges the fuel from the fuel injection valve side when the fuel pressure on the fuel injection valve side reaches at least a predetermined valve opening pressure. The fuel pressure raising unit raises the fuel pressure on the fuel injection valve side to at least the predetermined valve opening pressure of the relief valve prior to the automatic stop.

Thus, during the pressure raise continuation duration after the fuel pressure raising means raises the fuel pressure to or above the set valve opening pressure of the relief valve, the fuel pressure raising means further continues the process of raising the fuel pressure to or above the predetermined valve opening pressure of the relief valve. Therefore, during the pressure raise continuation duration just prior to the automatic stop, the relief valve is continuously or repeatedly opened, so that a large amount of fuel can be delivered toward the fuel injection valve side and a large amount of fuel can be discharged via the relief valve. Hence, in addition to achieving sufficient improvements in fuel economy and the like by increasing the frequency of performing the compression-stroke injection following an automatic start, the control apparatus is able to prevent the fixation of the relief valve or the clogging thereof with a foreign matter, which is likely to occur after the relief valve has not been opened for a long time.

Furthermore, by setting the pressure raise continuation duration, it becomes possible to deliver a large amount of fuel toward the fuel injection valve side and discharge a large amount of fuel via the relief valve. Thus, a reduced fuel temperature on the fuel injection valve side can be achieved immediately before the automatic stop. Hence, it becomes possible to maintain a sufficiently high fuel pressure achieved by thermal expansion caused by increases in the fuel temperature during the automatic stop of the engine. Consequently, the frequency of performing the compression-stroke injection following an automatic stop can be further increased, and improvements in fuel economy and the like can be more effectively achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic diagram illustrating a construction of a direct injection type internal combustion engine in accordance with Embodiment 1;

FIG. 2

is a block diagram of a control system of the direct injection type internal combustion engine in accordance with Embodiment 1;

FIG. 3

is a horizontal sectional view of a cylinder head in Embodiment 1;

FIG. 4

is a plan view of a top surface of a piston in Embodiment 1;

FIG. 5

is a section taken on line X—X in

FIG. 3

;

FIG. 6

is a section taken on line Y—Y in

FIG. 3

;

FIG. 7

is a diagram illustrating the construction of a fuel supply system in Embodiment 1;

FIG. 8

is a flowchart illustrating an operation mode setting process in Embodiment 1;

FIG. 9

is a diagram illustrating the construction of a map for determining a lean fuel injection amount QL in Embodiment 1;

FIG. 10

is a diagram illustrating the construction of a map for setting a mode of operation in Embodiment 1;

FIG. 11

is a flowchart illustrating a fuel injection amount control process in Embodiment 1;

FIG. 12

is a diagram illustrating the construction of a map for determining a stoichiometric air-fuel ratio basic fuel injection amount QBS in Embodiment 1;

FIG. 13

is a flowchart illustrating a high-load increase amount OTP calculating process executed in Embodiment 1;

FIG. 14

is a flowchart illustrating an electromagnetic spill valve control process in Embodiment 1;

FIG. 15

is a timing chart illustrating an example of the electromagnetic spill valve control in Embodiment 1;

FIG. 16

is a diagram illustrating the construction of a map for determining a target fuel pressure Pt in Embodiment 1;

FIG. 17

is a flowchart illustrating an automatic stop control process in Embodiment 1;

FIG. 18

is a flowchart illustrating an automatic start control process in Embodiment 1;

FIG. 19

is a timing chart illustrating an example of the control of the fuel pressure P in Embodiment 1;

FIG. 20

is a timing chart illustrating an example of the control of the fuel pressure P in Embodiment 2;

FIG. 21

is a flowchart illustrating an automatic stop control process in Embodiment 3; and

FIG. 22

is a flowchart illustrating an electromagnetic spill valve control process in Embodiment 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

FIG. 1

schematically illustrates a direct injection type internal combustion engine to which the above-described invention is applied.

FIG. 2

shows a block diagram of a control system of the direct injection type internal combustion engine.

A gasoline engine (hereinafter, referred to as an “engine”)

2

provided as a direct injection type internal combustion engine is installed in a motor vehicle for driving the vehicle. The engine

2

has six cylinders

2

a

. As shown in

FIGS. 3

to

6

, each cylinder

2

a

has a combustion chamber

10

that is defined by a cylinder block

4

, a piston

6

provided for reciprocating movements within the cylinder block

4

, and a cylinder head

8

disposed on top of the cylinder block

4

.

Each combustion chamber

10

is provided with a first intake valve

12

a

, a second intake valve

12

b

, and a pair of exhaust valves

16

. The first intake valve

12

a

is connected to a first intake port

14

a

. The second intake valve

12

b

is connected to a second intake port

14

b

. The two exhaust valves

16

are connected to two exhaust ports

18

, respectively.

FIG. 3

is a horizontal sectional view of a portion of the cylinder head

8

corresponding to a cylinder. As shown in

FIG. 3

, the first intake port

14

a

and the second intake port

14

b

of each cylinder are straight intake ports that extend substantially linearly. An ignition plug

20

is disposed in a central portion of an inner wall surface of the cylinder head

8

. A fuel injection valve

22

is disposed in a peripheral portion of an inner wall surface of the cylinder head

8

that is adjacent to both the first intake valve

12

a

and the second intake valve

12

b

. Each fuel injection valve

22

is disposed so that fuel can be injected therefrom directly into the combustion chamber.

FIG. 4

is a plan view of a stop surface of a piston

6

.

FIG. 5

is a section taken on line X—X in FIG.

3

.

FIG. 6

is a section taken on line Y—Y in FIG.

3

. As shown in the drawings, a generally ridge-shaped top face of the piston

6

has a recess

24

having an inverted dome-like contour which extends from a site below the fuel injection valve

22

to a site below the ignition plug

20

.

As shown in

FIG. 1

, the first intake ports

14

a

of the cylinders

2

a

are connected to a surge tank

32

via first intake passages

30

a

formed in an intake manifold

30

. The second intake ports

14

b

are connected to the surge tank

32

via second intake passages

30

b

. An airflow control valve

34

is disposed within each second intake passage

30

b

. The airflow control valves

34

are interconnected via a common shaft

36

, and are opened and closed via the shaft

36

by a negative pressure actuator

37

. When the airflow control valves

34

are closed, intake air introduced via only the first intake ports

14

a

form strong swirls s (

FIG. 3

) within the combustion chambers

10

.

The surge tank

32

is connected to an air cleaner

42

via an intake duct

40

. A throttle valve

46

driven by an electric motor

44

(a DC motor or a step motor) is disposed in the intake duct

40

. The degree of opening of the throttle valve

46

(degree of throttle opening TA) is detected by a throttle opening sensor

46

a

. The degree of opening of the throttle valve

46

is controlled in accordance with the operating state. The exhaust ports

18

of the cylinders

2

a

are connected to an exhaust manifold

48

. The exhaust manifold

48

discharges exhaust gas, via a catalytic converter

49

for emission control.

FIG. 7

illustrates a construction of a fuel supply system for supplying high-pressure fuel toward the fuel injection valves

22

. As shown in

FIG. 7

, a fuel distribution pipe

50

is provided in a portion of the cylinder head

8

located near the first intake valves

12

a

and the second intake valves

12

b

. The fuel distribution pipe

50

is connected to the fuel injection valve

22

of each cylinder

2

a

. Fuel supplied from the fuel distribution pipe

50

is injected from the fuel injection valves

22

directly into the corresponding combustion chambers

10

.

The fuel distribution pipe

50

for distributing fuel to the fuel injection valves

22

is connected to a high-pressure fuel pump

54

via a high-pressure fuel passage

54

a

. The high-pressure fuel passage

54

a

is provided with a check valve

54

b

that restricts reverse flow of fuel from the fuel distribution pipe

50

toward the high-pressure fuel pump

54

. A feed pump

58

provided within a fuel tank

56

is connected to the high-pressure fuel pump

54

via a low-pressure fuel passage

54

c.

The feed pump

58

draws fuel present in the fuel tank

56

and ejects fuel toward the low-pressure fuel passage

54

c

, thereby delivering fuel into a gallery

54

i

of the high-pressure fuel pump

54

via a filter

58

a

and a pressure regulator

58

b.

The high-pressure fuel pump

54

is mounted on a cylinder head cover (not shown) that covers an upper portion of the cylinder head

8

. A plunger

54

e

is reciprocated within a pump cylinder

54

d

of the high-pressure fuel pump

54

, by rotation of a pump cam

2

c

provided on a cam shaft

2

b

of the intake valves or exhaust valves of the engine

2

. Due to the reciprocating movements of the plunger

54

e

, the high-pressure fuel pump

54

operates as follows. That is, during the suction stroke during which the capacity of a high-pressure pump chamber

54

f

increases, the high-pressure fuel pump

54

sucks fuel into the high-pressure pump chamber

54

f

from the side of low-pressure fuel passage

54

c

via the gallery

54

i

. During the pressurization stroke during which the capacity of the high-pressure pump chamber

54

f

decreases, the high-pressure fuel pump

54

delivers fuel pressurized in the high-pressure pump chamber

54

f

to the side of the fuel distribution pipe

50

via the high-pressure fuel passage

54

a

at a needed timing.

An electromagnetic spill valve

55

is provided within the high-pressure fuel pump

54

. The electromagnetic spill valve

55

is an open-close valve for connecting and disconnecting the gallery

54

i

and the high-pressure pump chamber

54

f

in communication. While the electromagnetic spill valve

55

is open, the gallery

54

i

and the high-pressure pump chamber

54

f

are connected in communication. Therefore, fuel drawn into the high-pressure pump chamber

54

f

spills to the side of the low-pressure fuel passage

54

c

via the gallery

54

i

during the pressurization stroke. Thus, while the electromagnetic spill valve

55

is open, fuel is not pressurized, and is not delivered toward the fuel distribution pipe

50

via the high-pressure fuel passage

54

a.

In contrast, when the electromagnetic spill valve

55

is closed, the communication between the gallery

54

i

and the high-pressure pump chamber

54

f

is shut off. Therefore, during the pressurization stroke, fuel in the high-pressure pump chamber

54

f

does not spill into the gallery

54

i

, but is pressurized to a high pressure by the pressing movement of the plunger

54

e

. Therefore, the check valve

54

b

is opened, so that high-pressure fuel is delivered toward the fuel distribution pipe

50

via the high-pressure fuel passage

54

a.

An electronic control unit (hereinafter, referred to as “ECU”)

60

controls the open-close timing of the electromagnetic spill valve

55

with reference to the fuel pressure P detected by a fuel pressure sensor

50

a

attached to the fuel distribution pipe

50

and the amount of fuel injection Q separately controlled by the ECU

60

. Thus, the ECU

60

is able to adjust the amount of fuel delivered from the high-pressure fuel pump

54

toward the fuel distribution pipe

50

, and is also able to adjust the fuel pressure P in the fuel distribution pipe

50

to a needed pressure.

A discharge path

54

h

having a relief valve

54

g

is connected to the fuel distribution pipe

50

. If the fuel pressure P in the fuel distribution pipe

50

exceeds a set valve opening pressure due to an excessive supply of fuel to the side of the fuel distribution pipe

50

, the relief valve

54

g

is opened to discharge an excess amount of fuel toward the discharge path

54

h

, and thereby keeps the fuel pressure in the fuel distribution pipe

50

at or below the set valve opening pressure. The fuel discharged toward the discharge path

54

h

is returned toward the gallery

54

i

. Thus, the fuel supply system is formed as a return-less fuel supply system in which an excess amount of fuel on the side of the fuel distribution pipe

50

is not returned directly to the fuel tank

56

.

In the return-less fuel supply system, the fuel pressure in a passage from the discharge path

54

h

to the low-pressure fuel passage

54

c

tends to rise when fuel is returned from the side of the fuel distribution pipe

50

to the discharge path

54

h

. When the fuel pressure in the low-pressure system tends to rise, the pressure regulator

58

b

in the fuel tank

56

becomes opened. Therefore, of the amount of fuel present within the low-pressure fuel passage

54

c

, an amount of fuel present near the pressure regulator

58

b

, that is, an amount of fuel just pumped up from the fuel tank

56

by the feed pump

58

, is returned from the pressure regulator

58

b

into the fuel tank

56

. Thus, a rise in the fuel pressure in the low-pressure system extending from the discharge path

54

h

to the low-pressure fuel passage

54

c

is prevented. Furthermore, since the amount of fuel returned into the fuel tank

56

is the amount of fuel just pumped up from the fuel tank

56

, a temperature increase in the fuel tank

56

can be prevented.

As shown in

FIG. 2

, the ECU

60

is formed by a digital computer that has a CUP (microprocessor)

60

b

, a ROM (read-only memory)

60

c

, a RAM (random access memory), a backup RAM

60

e

, an input circuit

60

f

, and an output circuit

60

g

that are interconnected by a bidirectional bus

60

a.

The throttle opening sensor

46

a

for detecting the degree of throttle opening TA inputs to the input circuit

60

f

an output voltage proportional to the degree of opening TA of the throttle valve

46

. An accelerator pedal

74

is provided with an accelerator depression sensor

76

that inputs to the input circuit

60

f

an output voltage proportional to the amount ACCP of depression of the accelerator pedal

74

. A stop lamp switch

80

for detecting a state of depression of a brake pedal

78

inputs a stop lamp switch signal SLSW to the input circuit

60

f

. A revolution sensor

82

generates an output pulse at every 30° rotation of a crankshaft (not shown), and inputs the output pulse to the input circuit

60

f

. A cylinder discrimination sensor

84

generates an output pulse when, for example, a No.

1

cylinder of the cylinders

2

a

reaches the intake top dead center, and inputs the output pulse to the input circuit

60

f

. The CPU

60

b

calculates a present crank angle based on output pulses from the cylinder discrimination sensor

84

and output pulses from the revolution sensor

82

, and calculates an engine revolution speed NE based on the frequency of output pulses from the revolution sensor

82

.

The cylinder block

4

of the engine

2

is provided with a water temperature sensor

86

. The water temperature sensor

86

detects the temperature THW of cooling water of the engine

2

, and inputs to the input circuit

60

f

an output voltage corresponding to the cooling water temperature THW. The surge tank

32

is provided with an intake pressure sensor

88

. The intake pressure sensor

88

inputs to the input circuit

60

f

an output voltage corresponding to the intake pressure (pressure of intake air (absolute pressure)) PM in the surge tank

32

. The exhaust manifold

48

is provided with an air-fuel ratio sensor

90

. The air-fuel ratio sensor

90

inputs to the input circuit

60

f

an output voltage Vox in accordance with the air-fuel ratio. The fuel pressure sensor

50

a

provided on the fuel distribution pipe

50

inputs to the input circuit

60

f

an output voltage in accordance with the fuel pressure P in the fuel distribution pipe

50

. A voltage VB of a battery

92

installed in the vehicle is inputted to the input circuit

60

f

. Furthermore, an output side of the transmission apparatus (not shown) is provided with a vehicle speed sensor

94

. The vehicle speed sensor

94

inputs to the input circuit

60

f

a signal generated in accordance with the vehicle speed SPD based on rotation of an output shaft of the transmission.

The output circuit

60

g

is connected to the fuel injection valves

22

, the negative pressure actuator

37

, the drive motor

44

for the throttle valve

46

, the electromagnetic spill valve

55

, an igniter

100

, and a starter motor

102

, and drives and controls the actuator units

22

,

37

,

45

,

55

,

100

,

102

in accordance with needs.

A fuel injection control performed after the engine

2

has been started will next be described. The flowchart of

FIG. 8

illustrates a process of setting a mode of operation needed for the fuel injection control. This process is periodically executed at every pre-set crank angle. The individual process steps in the flowchart described below will be referred to as “S”.

In S

100

, the engine revolution speed NE acquired from the signal from the revolution sensor

82

, the amount of depression of the accelerator pedal

74

(hereinafter, referred to as “accelerator pedal depression”) ACCP acquired from the signal from the accelerator depression sensor

76

, and the fuel pressure P acquired from the signal from the fuel pressure sensor

50

a

are inputted into work areas of the RAM

60

d.

Subsequently in S

102

, a lean fuel injection amount QL is calculated based on the engine revolution speed NE and the accelerator pedal depression ACCP. The lean fuel injection amount QL represents an optimal fuel injection amount for bringing the output toque of the engine

2

to a requested torque during performance of stratified charge combustion. The lean fuel injection amount QL is empirically determined, and is pre-stored in the ROM

60

c

in the form of a map that employs the accelerator pedal depression ACCP and the engine revolution speed NE as parameter as indicated in FIG.

9

. In S

102

, the lean fuel injection amount QL is calculated based on the aforementioned map. In the map, values are discretely arranged. Therefore, if there is no value that matches as a parameter, a suitable value is determined by interpolation. This manner of determining a value from the map through interpolation is likewise performed in determining values from maps other than the aforementioned map, as well.

Subsequently in S

104

, it is determined whether the actually measured fuel pressure P is at least a reference pressure Pc, that is, whether the actually measured fuel pressure P is a fuel pressure that sufficiently allows fuel injection during the compression stroke for the purpose of stratified charge combustion.

If “YES” in S

104

, that is, if P≧Pc, it is possible to perform sufficient fuel injection during the compression stroke. Then, the process proceeds to S

106

. In S

106

, based on the lean fuel injection amount QL and the engine revolution speed NE, an operation mode is set corresponding to one of three regions R

1

, R

2

, R

3

as indicated in the map of FIG.

10

. After that, the process is temporarily ended. The map of

FIG. 10

is prepared beforehand by empirically setting suitable modes of operation in accordance with the lean fuel injection amount QL and the engine revolution speed NE. The map is stored in the ROM

60

c

as a map that employs the lean fuel injection amount QL and the engine revolution speed NE as parameters.

Referring to

FIG. 10

, in the operation region R

1

where the lean fuel injection amount QL and the engine revolution speed NE are less than a boundary line QQ

1

, a mode F

1

is selected as a mode of operation. In the operation mode F

1

, an amount of fuel corresponding to the lean fuel injection amount QL is injected during a late period in the compression stroke. Injected fuel provided by injected performed during the late period of the compression stroke moves from the fuel injection valve

22

into the recess

24

of the piston

6

in each cylinder, and then strikes a peripheral wall surface

26

(

FIGS. 4

,

5

). Upon striking the peripheral wall surface

26

, fuel vaporizes and forms a combustible mixture layer in the recess

24

adjacent to the ignition plug

20

. The stratified combustible mixture is ignited by the ignition plug

20

, thereby accomplishing stratified charge combustion. In this manner, stable combustion can be accomplished in the combustion chambers with intake air existing in an extremely excess amount relative to fuel.

In the operation region R

2

where the lean fuel injection amount QL and the engine revolution speed NE are between the boundary line QQ

1

and a boundary line QQ

2

, a mode F

2

is selected as a mode of operation. In the operation mode F

2

, an amount of fuel corresponding to the lean fuel injection amount QL is injected dividedly twice, that is, once during the intake stroke and once during the late period of the compression stroke. That is, the first fuel injection is performed during the intake stroke, and the second fuel injection is performed during the late period of the compression stroke. The first injected fuel flows together with intake air into the combustion chamber

10

, and thereby forms a uniform lean mixture in the entire space of the combustion chamber

10

. Furthermore, as a result of the second fuel injection performed during the late period of the compression stroke, a combustible mixture layer is formed within the recess

24

adjacent to the ignition plug

20

as described above. The stratified combustible mixture is ignited by the ignition plug

20

, and the ignited flame burns the lean mixture filling the entire combustion chamber

10

. That is, in the operation mode F

2

, stratified charge combustion is performed at a reduced degree of stratification in comparison with the operation mode F

1

. In this manner, smooth torque changing can be realized in an intermediate region between the operation region R

1

and the operation region R

3

.

In the operation region R

3

where the lean fuel injection amount QL and the engine revolution speed NE are greater than the boundary line QQ

2

, a mode F

3

is set as a mode of operation. In the operation mode F

3

, the amount of fuel corrected in various manners based on a stoichiometric air-fuel ratio basic fuel injection amount QBS is injected during the intake stroke. The thus-injected fuel enters the combustion chamber

10

together with an inflow of intake air, and moves until ignition. This flowing movement forms a uniform mixture that uniformly exists in the entire combustion chamber

10

at the stoichiometric air-fuel ratio (in some cases, the air-fuel ratio is controlled to a rich air-fuel ratio that means a higher fuel concentration than the stoichiometric air-fuel ratio, due to an increasing control as described below). As a result, uniform combustion is accomplished. Conversely, if “NO” in S

104

, that is, if P<Pc, the low fuel pressure P makes it impossible to perform sufficient fuel injection during the compression stroke. Then, the process proceeds to S

108

, in which the mode F

3

is set as a mode of operation. The process is then temporarily ended.

FIG. 11

shows a flowchart of a fuel injection amount control process that is executed based on the mode of operation set by the above-described operation mode setting process. The process illustrated in

FIG. 11

is periodically executed at every pre-set crank angle.

After the fuel injection amount control process starts, the accelerator pedal depression ACCP acquired from the signal from the accelerator depression sensor

76

, the engine revolution speed NE acquired from the signal from the revolution sensor

82

, the intake pressure PM acquired from the signal from the intake pressure sensor

88

, and the detected air-fuel ratio value Vox acquired from the signal from the air-fuel ratio sensor

90

are inputted to work areas of the RAM

60

d

in S

120

.

Subsequently in S

126

, it is determined whether the operation mode F

3

has been set by the operation mode setting process illustrated in FIG.

8

. If “YES” in S

126

, that is, if it is determined that the operation mode F

3

has been set, the process proceeds to S

130

. In S

130

, a stoichiometric air-fuel ratio basic fuel injection amount QBS is calculated from the intake pressure PM and the engine revolution speed NE, using a map of

FIG. 12

pre-set in the ROM

60

c.

Subsequently in S

140

, a high-load increase amount OTP calculating process is executed. The high-load increase amount OTP calculating process will be described with reference to the flowchart of FIG.

13

. In the high-load increase amount OTP calculating process, first in S

141

, it is determined whether the accelerator pedal depression ACCP is greater than a high-load increase amount criterion KOTPAC. If “NO” in S

141

, that is, if ACCP≦KOTPAC, the process proceeds to S

142

, in which a value “0” is set as the high-load increase amount OTP. This means that the fuel increasing correction is not performed. Then, the high-load increase amount OTP calculating process is temporarily ended. Conversely, if “YES” in S

141

, that is, if ACCP>KOTPAC, the process proceeds to S

144

, in which a value M (e.g., 1>M>0) is set as the high-load increase amount OTP. Thus, execution of the fuel increase correction is set. This increasing correction is performed in order to prevent the overheating of the catalytic converter

49

during a high-load operation.

Referring back to

FIG. 11

, after the high-load increase amount OTP is calculated in S

140

, the process proceeds to S

150

, in which it is determined whether an air-fuel ratio feedback condition is met. For example, it is determined whether all the following conditions are met: (1) the engine is not being started; (2) warm-up has been completed (e.g., cooling water temperature THW≧40° C.); (3) the air-fuel ratio sensor

90

has been activated; and (4) the value of the high-load increase amount OTP is “0”.

If “YES” in S

150

, that is, if the air-fuel ratio feedback condition is met, the process proceeds to S

160

, in which an air-fuel ratio feedback factor FAF and a learned value KG thereof are calculated. The air-fuel ratio feedback factor FAF is calculated based on the output of the air-fuel ratio sensor

90

. The learned value KG is provided for storing a deviation of the air-fuel ratio feedback factor FAF from a center value “1.0”. With regard to the air-fuel ratio feedback control technology employing the aforementioned values, various techniques are known as disclosed in Japanese Patent Application Laid-Open No. HEI 6-10736 and the like.

Conversely, if “NO” in S

150

, that is, if the air-fuel ratio feedback condition is not met, the process proceeds to S

170

, in which the air-fuel ratio feedback factor FAF is set to 1.0. After S

160

or S

170

, the process proceeds to S

180

, in which an amount of fuel injection Q is determined as in Equation 1.

Q→QBS

{1

+OTP

+(

FAF

−1.0)+(

KG

−1.0)}α+β [Eq. 1]

where α and β are factors that are suitably set in accordance with the kind of the engine

2

, the content of control, etc.

After that, the fuel injection amount control process is temporarily ended.

If “NO” in S

126

, that is, if the present operation mode is other than the operation mode F

3

, that is, either one of the operation modes F

1

and F

2

, the process proceeds to S

190

. In S

190

, the lean fuel injection amount QL determined in S

102

in the operation mode setting process (

FIG. 8

) is set as an amount of fuel injection Q. After that, the fuel injection amount control process is temporarily ended.

An electromagnetic spill valve control process for controlling the amount of fuel delivered from the high-pressure fuel pump

54

to the fuel distribution pipe

50

will be described with reference to the flowchart of FIG.

14

. This process is periodically executed at every pre-set crank angle.

After the electromagnetic spill valve control process starts, the amount of fuel injection Q calculated in the fuel injection amount control process illustrated in

FIG. 11

, the lean fuel injection amount QL calculated as a value corresponding to the engine load in S

102

of the operation mode setting process illustrated in

FIG. 8

, the engine revolution speed NE detected by the revolution sensor

82

, and the fuel pressure P in the fuel distribution pipe

50

detected by the fuel pressure sensor

50

a

are inputted to work areas of the RAM

60

d

in S

210

.

Subsequently in S

220

, it is determined whether an immediately-before-automatic-stop flag XPREEC related to the engine

2

is “OFF”. The immediately-before-automatic-stop flag XPREEC is a flag that is turned “ON” immediately before the automatic stop is performed after the automatic stop condition is met, as described below.

If “NO” in S

220

, that is, if XPREEC=“ON”, the process proceeds to S

230

, in which a control duty DT that sets a closed valve duration (delivery duration) of the electromagnetic spill valve

55

is set to “100%”. The control duty DT represents the proportion of the closed duration of the electromagnetic spill valve

55

to the entire duration of the pressurization stroke of the high-pressure fuel pump

54

, during which the capacity of the high-pressure pump chamber

54

f

is decreased by the plunger

54

e

. As indicated in

FIG. 15

, DT=100% means that the electromagnetic spill valve

55

remains closed during the entire pressurization stroke, and therefore, the entire duration of the pressurization stroke is an ejection duration Tout of ejection from the high-pressure fuel pump

54

toward the fuel distribution pipe

50

. That is, the control duty DT=100% represents a state in which the amount of delivery from the high-pressure fuel pump

54

is adjusted to a maximum.

Subsequently in S

240

, the aforementioned control duty DT is set as a control duty that represents the closed valve duration of the electromagnetic spill valve

55

during the pressurization stroke of the high-pressure fuel pump

54

. After that, the electromagnetic spill valve control process is temporarily ended.

In the case of XPREEC=“ON”, the amount of delivery from the high-pressure fuel pump

54

to the fuel distribution pipe

50

reaches a maximum, and the fuel pressure P in the fuel distribution pipe

50

rapidly rises. If this state continues, the fuel pressure P reaches a set valve opening pressure of the relief valve

54

g

(e.g., 14.0 to 14.5 MPa), so that fuel starts to be discharged via the relief valve

54

g

into the discharge path

54

h.

If “YES” in S

220

, that is, if XPREEC=“OFF”, the process proceeds to

5250

, in which a feed-forward term FF is calculated based on the product (Kf·Q) of the amount of fuel injection Q and a feed-forward factor Kf.

Subsequently in S

260

, a target fuel pressure Pt is calculated by using a map that employs, as parameters, the engine revolution speed NE and the lean fuel injection amount QL corresponding to the engine load as indicated in FIG.

16

. This map is pre-set by determining target fuel pressures Pt indicating a suitable fuel injection state, in accordance with the lean fuel injection amount QL and the engine revolution speed NE based on an experiment. The map is stored in the ROM

60

c.

Subsequently in S

270

, a pressure deviation ΔP between the target fuel pressure Pt and the actual fuel pressure P is calculated as in Equation 2.

Δ

P→Pt−P

[Eq. 2]

Subsequently in S

280

, a proportional term DTp is calculated from the product of the pressure deviation ΔP and a proportionality factor K1. Subsequently in S

290

, an integral term DTi is calculated based on the product (K2·ΔP) of the pressure deviation ΔP and an integration factor K2, as in Equation 3.

DTi→DTi+K

2

·ΔP

[Eq. 3]

In Equation 3, “DTi” on the right-hand side represents the integral term DTi calculated during the previous control cycle, and the initial value thereof is set to, for example, “0”.

Subsequently in S

300

, a control duty DT for setting the closed valve duration (delivery duration) of the electromagnetic spill valve

55

is calculated as in Equation 4.

DT→Ka

(

DTp+DTi+FF

) [Eq. 4]

where Ka is a correction factor.

After the control duty DT is thus determined, this control duty DT is set in S

240

as a control duty that represents the closed valve duration of the electromagnetic spill valve

55

during the pressurization stroke of the high-pressure fuel pump

54

. After that, the process is temporarily ended.

If “YES” in S

220

, that is, if the immediately-before-automatic-stop flag XPREEC is “OFF” as mentioned above, the target fuel pressure Pt calculated in S

260

is set to an appropriate value within the range of, for example, 8.0 to 13.0 MPa.

Next, the automatic stop control process is illustrated in the flowchart of FIG.

17

. This process is periodically executed at every pre-set short time. In this process, the setting of the aforementioned immediately-before-automatic-stop flag XPREEC is performed as well as the automatic stop control process of the engine

2

.

When the automatic stop control process starts, the operating state for determining whether to execute the automatic stop is inputted in S

410

. For example, the cooling water temperature THW detected by the water temperature sensor

86

, the presence/absence of a depression of the accelerator pedal

74

detected by the accelerator depression sensor

76

, the voltage VB of the battery

92

, the presence/absence of a depression of the brake pedal

78

detected from the stop lamp switch signal SLSW from the stop lamp switch

80

, and the vehicle speed SPD detected from the signal from the vehicle speed sensor

94

are inputted to work areas of the RAM

60

d.

Subsequently in S

420

, it is determined from the operating states whether an automatic stop condition is met. It is determined that the automatic stop condition is met, if, for example, all the following conditions are met: (1) the engine

2

has been warmed up and is not overheated (the cooling water temperature THW is lower than a water temperature upper limit value THWmax, and is higher than a water temperature lower limit value THWmin); (2) the accelerator pedal

74

is not depressed (the accelerator pedal depression ACCP=0°); (3) the amount of charge in the battery

92

is at least a certain amount (the voltage VB is at least a reference voltage); (4) the brake pedal

78

is depressed (the stop lamp switch signal SLSW is “ON”); and (5) the vehicle is stopped (the vehicle speed SPD is 0 km/h).

If “NO” in S

420

, that is, if any one of the aforementioned conditions (1) to (5) is unmet, it is determined that the automatic stop condition is not met. Then, the process is temporarily ended.

Conversely, if “YES” in S

420

, that is, if the automatic stop condition is met because, for example, the operating person stops the vehicle at an intersection or the like, the process proceeds to S

430

, in which the immediately-before-automatic-stop flag XPREEC is set to “ON”. As a result, negative determination is made in S

220

in the above-described electromagnetic spill valve control process illustrated in

FIG. 14

, and the control duty DT=100% is set in S

230

. Thus, the fuel pressure P is raised to an increased level in comparison with an ordinary operating state.

Subsequently in S

440

of the automatic stop control process, it is determined whether a timer counter TC has reached or exceeded a pressure raise continuation duration Tx. If “NO” in S

440

, that is, if it is determined that TC<Tx, the process proceeds to S

450

, in which the counting-up of the timer counter TC is executed as expressed in Equation 5. After that, the process is temporarily ended.

TC→TC+dT

[Eq. 5]

In Equation 5, dT is a control cycle of the automatic stop control process. That is, the timer counter TC measures time that elapses after the automatic stop condition is met. The pressure raise continuation duration Tx is a reference time provided for determining from elapse of time whether the raise of the fuel pressure P that needs to be accomplished immediately prior to the automatic stop has been completed. A value of the pressure raise continuation duration Tx is set by empirically determining a time needed for the fuel pressure P to sufficiently rise if the control duty DT=100(%) is set.

If “YES” in S

420

, that is, until the pressure raise continuation duration Tx elapses after the automatic stop condition has been met, the process of S

410

, S

420

, S

430

, S

440

, S

450

is repeated. Therefore, XPREEC=“ON” is maintained, and the state of control duty DT=100(%) with respect to the electromagnetic spill valve

55

continues. If “YES” in S

440

, that is, if TC≧Tx as a result of the counting up in S

450

, the process proceeds to S

460

, in which the setting for stopping the fuel injection amount control process illustrated in

FIG. 11

is made. Subsequently in S

470

, the setting for stopping an ignition control process (not illustrated in detail) is made. As a result, the fuel injection and the ignition stop, so that the operation of the engine

2

immediately stops. Due to the stop of the engine

2

, the driving of the high-pressure fuel pump

54

also stops, and the check valve

54

b

is closed. Therefore, the inside of the fuel distribution pipe

50

is tightly closed in a high-pressure fuel state achieved by raising the fuel pressure from an ordinary level (the pressure being not higher than the set valve opening pressure of the relief valve

54

g

) due to the control duty DT=100(%) immediately before the stop of the engine

2

.

Subsequently in S

480

, the setting for a stop is also made with respect to the electromagnetic spill valve control process illustrated in

FIG. 14

, and the output of the control duty signal is stopped.

Subsequently in S

490

, a start of an automatic start control process described below is set. After that, the process is temporarily ended.

After the stop settings for the fuel injection amount control process, the ignition control process and the electromagnetic spill valve control process (S

460

, S

470

, S

480

) and the start setting for the automatic start control process (S

490

) have been made, the stopped states of the aforementioned controls and the execution of the automatic start control process continue until the start settings for the controls and the stop setting for the automatic start control process are made, even if negative determination is made (“NO”) in S

420

, that is, even if the automatic stop condition is unmet.

The automatic start control process is illustrated in the flowchart of FIG.

18

. This process is periodically executed at every pre-set short time.

After the automatic start control process starts, the operating state of the engine

2

is inputted in S

510

in order to determine whether to substantially execute the automatic start process. For example, similar to the data inputted in S

410

, the cooling water temperature THW, the accelerator pedal depression ACCP, the voltage VB of the battery

92

, the stop lamp switch signal SLSW, and the vehicle speed SPD are inputted to work areas of the RAM

60

d.

Subsequently in S

520

, it is determined from the operating states whether an automatic start condition is met. It is determined that the automatic start condition is met if, for example, any one of the following conditions (1) to (5) is unmet: (1) the engine

2

has been warmed up and is not overheated (the cooling water temperature THW is lower than the water temperature upper limit value THWmax, and is higher than the water temperature lower limit value THWmin); (2) the accelerator pedal

74

is not depressed (the accelerator pedal depression ACCP=0°); (3) the amount of charge in the battery

92

is at least a certain amount (the voltage VB is at least a reference voltage); (4) the brake pedal

78

is depressed (the stop lamp switch signal SLSW is “ON”); and (5) the vehicle is stopped (the vehicle speed SPD is 0 km/h). As for the automatic start condition, it is not altogether necessary to adopt the same conditions as the conditions (1) to (5) adopted for the automatic stop condition. That is, it is practicable to set conditions other than the conditions (1) to (5). It is also practicable to extract only some of the conditions (1) to (5).

If “NO” in S

520

, that is, if all the conditions (1) to (5) are met, it is determined that the automatic start condition is not met. After that, the process is temporarily ended.

Conversely, if “YES” in S

520

, that is, if any one of the conditions (1) to (5) is unmet, it is determined that the automatic start condition is met, and the process proceeds to S

530

. In S

530

, the immediately-before-automatic-stop flag XPREEC is set to “OFF”. Subsequently in S

540

, the timer counter TC is cleared to zero.

Subsequently in S

550

, execution of the automatic start process is set. Upon setting for executing the automatic start process, the starter motor

102

is driven to turn the crankshaft of the engine

2

, and the fuel injection amount control process and the ignition timing control process for an engine start are executed, so that the engine

2

is automatically started. After the starting is completed, the fuel injection amount control process illustrated in

FIG. 11

, the ignition control process (not illustrated), and the electromagnetic spill valve control process illustrated in

FIG. 14

, as well as other processes necessary for the driving of the engine

2

, are started.

After the execution setting for the automatic start process is made, the stop setting for the automatic start control process is made in S

560

. As a result, the automatic start control process stops.

The changing of the fuel pressure P in accordance with Embodiment 1 is illustrated in the timing chart of FIG.

19

.

For example, when the operating person stops the vehicle and keeps it in an idling state at an intersection or the like, the automatic stop condition is met at time point t

0

. That is, if “YES” in S

420

, the process proceeds to S

430

, in which the immediately-before-automatic-stop flag XPREEC is set to “ON”. As a result, in S

220

and S

230

, the control duty DT of the electromagnetic spill valve

55

is set to 100%, and the fuel pressure P rapidly rises beyond a during-idle fuel pressure control range (8 to 10 MPa in this embodiment) as indicated by a solid line, and reaches the set valve opening pressure of the relief valve

54

g

(14 to 14.5 MPa in this embodiment). Therefore, the relief valve

54

g

temporarily opens to discharge an excess amount of fuel from the fuel distribution pipe

50

into the discharge path

54

h

. After that, in S

460

and S

470

, the engine

2

is automatically stopped at time point t

1

at which the pressure raise continuation duration Tx elapses.

After that, residual heat from the engine

2

heats the amount of fuel contained in the fuel distribution pipe

50

, so that the fuel tends to expand and the fuel pressure P tends to rise in the fuel distribution pipe

50

. However, the relief valve

54

g

slightly opens so as to discharge an amount of fuel corresponding to the thermal expansion toward the discharge path

54

h

. Therefore, the fuel pressure P is kept substantially constantly at the set valve opening pressure of the relief valve

54

g

for a while.

After that, the thermal expansion diminishes, and then the fuel pressure P within the fuel distribution pipe

50

starts to decrease due to the leakage of fuel via the relief valve

54

g

. Then, the fuel pressure P continues falling as long as the engine

2

remains stopped. However, the fuel pressure P does not decrease below the fuel pressure control range (8 to 13 MPa in this embodiment) before time point t

3

. From time point t

3

on, the fuel pressure P becomes below the fuel pressure control range.

If the process of raising the fuel pressure P immediately prior to the engine automatic stop is not performed as in the case of the conventional art, the fuel pressure P temporarily rises slightly due to thermal expansion. However, after a short time (time point t

2

), the fuel pressure P decreases below the fuel pressure control range.

In the above-described process, S

220

, S

230

, S

430

, S

440

and S

450

correspond to a process as a fuel pressure raising means.

The first embodiment as described above achieves the following advantages.

(1-1) Due to the process of S

220

, S

230

, S

430

, S

440

and S

450

, the fuel pressure P is raised immediately prior to the automatic stop. Therefore, after the engine

2

stops and the delivery of high-pressure fuel from the high-pressure fuel pump

54

toward the fuel injection valves

22

stops, the pressure fall starts from an increased fuel pressure P in comparison with the case where the engine

2

is stopped with an ordinary fuel pressure state as in the conventional art. Therefore, an increased engine stop time is allowed before the fuel pressure decreases to a fuel pressure that makes it impossible to perform appropriate fuel injection into each combustion chamber

10

during the compression stroke. According to the first embodiment, the period between time points t

1

and t

3

is the period during which it is possible to perform appropriate fuel injection into each combustion chamber

10

during the compression stroke, as indicated in FIG.

19

. In contrast, according to the conventional art, the period between time points t

1

and t

2

is the period during which it is possible to perform appropriate fuel injection into each combustion chamber

10

during the compression stroke.

That is, according to the conventional art, if the automatic start is performed between time points t

2

and t

3

, negative determination is made (“NO”) in S

104

in

FIG. 8

immediately after the start of the engine

2

, so that the mode F

3

is set as a mode of operation. Thus, fuel injection during the compression stroke cannot be performed, and fuel injection during the intake stroke is performed. According to Embodiment 1, if the automatic start is performed between time points t

2

and t

3

, affirmative determination is made (“YES”) in S

104

in

FIG. 8

, so that the mode F

1

or F

2

can be set as a mode of operation to perform fuel injection during the compression stroke provided that the engine

2

is in an operating state that allows stratified charge combustion.

Therefore, it becomes possible to increase the frequency of performances of the compression-stroke injection after an automatic start. Hence, it becomes possible to sufficiently achieve improvements in fuel economy and the like.

(1-2) As a means for raising the fuel pressure P immediately prior to the automatic stop, the control duty DT of the electromagnetic spill valve

55

is set to 100% to adjust the amount of delivery from the high-pressure fuel pump

54

to a maximum.

By utilizing the range where the amount of delivery from the high-pressure fuel pump

54

is maximum, the fuel pressure P can be rapidly raised to a sufficiently high pressure state. Therefore, the frequency of performances of the compression-stroke injection after an automatic start further increases, and the fuel economy improvement becomes more effective.

(1-3) By maintaining the maximum amount of delivery from the high-pressure fuel pump

54

during the pressure raise continuation duration Tx immediately prior to the automatic stop, the fuel pressure P is raised to or above the set valve opening pressure of the relief valve

54

g

. This process provides an occasion of opening the relief valve

54

g

, which is scarcely ever opened during normal operation.

Therefore, it becomes possible to prevent the locking of the relief valve

54

g

or the clogging thereof with a foreign matter, which is likely to occur after the relief valve

54

g

has not been opened for a long time.

Second Embodiment

A second embodiment differs from Embodiment 1 described above in the length of the pressure raise continuation duration Tx related to step S

440

of the automatic stop control process (FIG.

17

). Other constructions of the second embodiment are the same as those of the first embodiment. That is, in addition to increasing the fuel pressure P to or above the set valve opening pressure of relief valve

54

g

immediately prior to the automatic stop, the second embodiment, after the set valve opening pressure of the relief valve

54

g

is reached or exceeded, keeps the control duty DT of the electromagnetic spill valve

55

at 100% until a certain amount of fuel is discharged from the fuel distribution pipe

50

via the relief valve

54

g

. Therefore, the pressure raise continuation duration Tx is set longer in this embodiment than in the first embodiment.

As a result, the relief valve

54

g

is opened repeatedly during a period Tmax as indicated in the timing chart of FIG.

20

. That is, while a large amount of fuel is being delivered from the high-pressure fuel pump

54

to the fuel distribution pipe

50

, a state in which a portion of the fuel delivered into the fuel distribution pipe

50

is discharged into the discharge path

54

h

via the relief valve

54

g

is repeated.

According to Embodiment 2 described above, the following advantages are achieved.

(2-1) The advantages (1-1) to (1-3) of the first embodiment are achieved.

(2-2) Even after the fuel pressure P is raised to or above the set valve opening pressure of the relief valve

54

g

, the process of raising the fuel pressure P to or above the set valve opening pressure of the relief valve

54

g

is continued for a while. As a result, immediately prior to the automatic stop, the relief valve

54

g

is repeatedly opened, and a large amount of fuel is delivered toward the fuel distribution pipe

50

, so that the fuel temperature in the fuel distribution pipe

50

drops immediately before the automatic stop.

Therefore, it is possible to maintain a sufficiently high fuel pressure achieved by thermal expansion caused by increases in the fuel temperature during the automatic stop of the engine

2

. Hence, the frequency of performing the compression-stroke injection after an automatic start can be further increased, and improvements in fuel economy and the like can be more effectively achieved.

Third Embodiment

In a third embodiment, it is determined whether to execute the automatic stop by monitoring the fuel pressure P. The automatic stop control process (

FIG. 17

) in the first embodiment is replaced by execution of a process illustrated in FIG.

21

. Other constructions of the third embodiment are the same as those of Embodiment 1. The automatic stop control process illustrated in

FIG. 21

differs from the automatic stop control process (

FIG. 17

) of the first embodiment only in the processing of S

1440

, S

1442

and S

1444

. The other steps in

FIG. 21

perform the same processing as in the steps in

FIG. 17

represented by step numbers equal to the three lower digits of the step numbers of the steps in FIG.

21

.

If “YES” in S

1420

, that is, if the automatic stop condition is met, the immediately-before-automatic-stop flag XPREEC is set to “ON” in S

1430

. Subsequently in S

1440

, it is determined whether the timer counter TC has reached or exceeded a time limit Ty. The time limit Ty is a criterion time provided for allowing the transition to the automatic stop without waiting for the raise in the fuel pressure P if the raise in the fuel pressure P is slow from any cause.

If “NO” in S

1440

, that is, if TC<Ty, it is then determined in S

1442

whether the fuel pressure P is less than, for example, a pressure raise criterion pressure value Pr that is set within a range from the upper limit value (e.g., 13 MPa in this embodiment) of the fuel pressure control range to the set valve opening pressure (e.g., 14 MPa) of the relief valve

54

g.

If “YES” in S

1442

, that is, P<Pr, the process proceeds to S

1450

, in which the counting-up of the timer counter TC is executed as in Equation 5. After that, the process is temporarily ended.

If “YES” in S

1420

, that is, while the time limit Ty has not elapsed after the automatic stop condition is met, the processing of S

1410

, S

1420

, S

1430

, S

1440

, S

1442

, S

1450

is repeated, so that XPREEC=“ON” is maintained. Thus, the state of control duty DT=100(%) with respect to the electromagnetic spill valve

55

continues.

If “NO” in S

1442

, that is, if P≧Pr is established due to increases in the fuel pressure P, the value of the time limit Ty is set in the timer counter TC in S

1444

. Subsequently in S

1460

, the stop setting for the fuel injection amount control process as illustrated in

FIG. 11

is made. Then, in S

1470

, the stop setting for the ignition control process is made. As a result, the fuel injection and the ignition stop, and the operation of the engine

2

immediately stops. Due to the stop of the engine

2

, the driving of the high-pressure fuel pump

54

also stops, and the check valve

54

b

is closed. Therefore, the inside of the fuel distribution pipe

50

is tightly closed in a high-pressure fuel state achieved by raising the fuel pressure from an ordinary level (the pressure being not higher than the set valve opening pressure of the relief valve

54

g

) due to the control duty DT=100(%) immediately before the stop o f the engine

2

. Subsequently in S

1480

, the setting for a stop is also made with respect to the electromagnetic spill valve control process (FIG.

14

), and the output of the control duty signal is stopped. Subsequently in S

1490

, a start of the automatic start control process (

FIG. 18

) is set. After that, the process is temporarily ended. In the above-described process, S

229

, S

230

(FIG.

14

), S

1430

and S

1442

correspond the processing as a fuel pressure raising means.

According to Embodiment 3 described above, then following advantages are achieved.

(3-1) The advantages (1-1) and (1-2) of Embodiment 1 are achieved.

(3-2) Since pressure rise is directly monitored based on the value of the fuel pressure P, the timing of the automatic stop can be more accurately determined. Therefore, the automatic stop can be executed during an early period, and improvements in fuel economy and the like can be more effectively achieved.

(3-3) The provision of the time limit Ty ensures the transition to the automatic stop even if the fuel pressure P is slow to rise from any cause.

Fourth Embodiment

A fourth embodiment raises the fuel pressure P by correcting the target fuel pressure Pt in the increasing direction immediately prior to the automatic stop, instead of setting the control duty DT to 100%. Therefore, a process illustrated in

FIG. 22

is executed in place of the electromagnetic spill valve control process (

FIG. 14

) of Embodiment 1. Other constructions of the fourth embodiment are the same as those of Embodiment 1. The steps of S

1210

, S

1250

, S

1260

, S

1270

to S

1300

, and S

1240

in

FIG. 22

, other than S

1262

and S

1264

of the electromagnetic spill valve control process, perform the same processing as in the steps in

FIG. 14

represented by step numbers equal to the three lower digits of the step numbers of the steps in FIG.

22

.

That is, after a target fuel pressure Pt is determined in S

1260

from the lean fuel injection amount QL and the engine revolution speed NE using the map indicated in

FIG. 16

, it is determined in S

1262

whether the immediately-before-automatic-stop flag XPREEC is “OFF”.

If “YES” in S

1262

, that is, if XPREEC=“OFF”, the process proceeds to S

1270

, in which a pressure deviation ΔP between the actual fuel pressure P and the target fuel pressure Pt calculated in S

1260

is calculated. Subsequently in S

1280

, a proportional term DTp is calculated from the product of the pressure deviation ΔP and the proportionality factor K1. Then, in S

1290

, an integral term DTi is calculated based on the product (K2·ΔP) of the pressure deviation ΔP and the integration factor K2, as expressed in Equation 3.

Subsequently in S

1300

, a control duty DT for setting the closed valve duration (delivery duration) of the electromagnetic spill valve

55

is calculated as expressed in Equation 4. Subsequently in S

1240

, this control duty DT is set as a control duty DT that represents the closed valve duration of the electromagnetic spill valve

55

in the pressurization stroke of the high-pressure fuel pump

54

. After that, the process is temporarily ended.

Conversely, if “NO” in S

1262

, that is, if XPREEC=“ON”, the target fuel pressure Pt is increased for correction in S

1264

, as expressed in Equation 6.

Pt→Pt+Pi

[Eq. 6]

where Pi represents an increasing correction value.

After that, in S

1270

, a pressure deviation ΔP between the actual fuel pressure P and the target fuel pressure Pt corrected to an increase side in S

1264

is calculated. After that, S

1280

to S

1300

are executed, so that a control duty DT is calculated. Subsequently in S

1240

, this control duty DT is set as a control duty that represents the closed valve duration of the electromagnetic spill valve

55

in the pressurization stroke of the high-pressure fuel pump

54

. After that, the process is temporarily ended.

Thus, if “NO” in S

1262

, that is, if XPREEC=“ON”, the fuel pressure P is adjusted so as to provide a pressure that is higher than usual.

In the above-described process, S

1262

and S

1264

, and S

430

, S

440

and S

450

(

FIG. 17

) correspond to the processing as a fuel pressure raising unit, and S

1210

, S

1250

, S

1260

, S

1270

to S

1300

, and S

1240

correspond to the processing as a fuel pressure control unit.

According to Embodiment 4 described above, the following advantage is achieved.

(4-1) The advantage (1-1) of the first embodiment is achieved.

Other Embodiments

In Embodiments 1 to 4, the pressure raise continuation duration Tx or the time limit Ty may also be set in accordance with the operating state of the engine

2

.

In Embodiment 4, the target fuel pressure Pt increased for correction in S

1264

may also be set to a value that is greater than or equal to the set valve opening pressure of the relief valve

54

g

, to open the relief valve

54

g

, so that the fixation of the relief valve

54

g

or the clogging thereof with a foreign matter can be prevented. Furthermore, after the actual fuel pressure P reaches a value that is greater than or equal to the set valve opening pressure of the relief valve

54

g

, the increasing correction of the target fuel pressure Pt in S

1264

may be continued so as to decrease the fuel temperature in the fuel distribution pipe

50

.

Although in the automatic stop control process (

FIGS. 17 and 21

) in Embodiments 1 and 3, the stop setting for the ignition control process is performed in S

470

and S

1470

, the stop setting for the ignition control process may be omitted since revolution of the engine

2

stops merely upon a stop of fuel injection.

While embodiments of the invention have been described, it is to be noted that embodiments of the invention further include the following forms.

(1) In a mode of the invention, an automatic stop permitting unit of the direct injection type internal combustion engine permits execution of the automatic stop when the fuel pressure on the fuel injection valve side is raised to a reference pressure by the fuel pressure raising unit.

(2) In a mode of the invention, an automatic stop permitting unit of the direct injection type internal combustion engine permits execution of the automatic stop when the elapsed time of the pressure raising process executed by the fuel pressure raising unit reaches or exceeds a reference time.

Number	Name	Date	Kind
3824978	Paquette	Jul 1974	A
3927652	O'Neill	Dec 1975	A
5977646	Lenz et al.	Nov 1999	A
20020033157	Thompson et al.	Mar 2002	A1

Number	Date	Country
A-10-47104	Feb 1998	JP
A-10-299543	Nov 1998	JP

Direct injection type internal combustion engine control apparatus and control method of the same

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Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

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US

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Abstract

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Claims

Priority Claims (1)

US Referenced Citations (4)

Foreign Referenced Citations (2)