Engine control device

Disclosed is a control device of an engine 1 including an injector. The injector has a needle which is displaced between a close position where no fuel is allowed to flow into a sac portion and an open position where the fuel is allowed to flow into the sac portion. The control device has a fuel injection controller controlling a fuel injection period and an injector controller controlling a motion of the needle. The injector controller executes control to reduce a moving speed of the needle before the needle reaches the closed position when the injection period ends.

TECHNICAL FIELD

The present disclosure relates to an engine control device including an injector injecting fuel in a combustion chamber within a cylinder.

BACKGROUND ART

An injector of this type has fuel injection holes positioned inside a combustion chamber in which combustion takes place. Consequently, solid contents such as carbon generated through combustion adhere to, and accumulate on, the injection holes and their periphery, forming what is called “deposit.” This phenomenon may hinder appropriate fuel injection.

The following specifically describes this point with reference toFIG. 1. Illustrations (a) to (c) inFIG. 1exemplify a tip end portion of an injector of this type exposed in the combustion chamber. A space (referred to as a sac portion101) into which pressurized fuel flows is formed within the tip end portion of the illustrated injector100. The sac portion101communicates with a combustion chamber103via a plurality of injection holes102.

Disposed within the injector100is a needle104slidingly displaceable between a close position where no fuel is allowed to flow into the sac portion101and an open position where the fuel is allowed to flow into the sac portion101. The displacement of the needle104is controlled at a high speed on the order of milliseconds.

As illustrated inFIG. 1(a), during fuel injection, the needle104is held at the open position, and the pressurized fuel flows into the sac portion101. Consequently, the fuel is injected into the combustion chamber103via the injection holes102. As illustrated in an illustration (b) inFIG. 1, when the fuel injection ends, the needle104is displaced to the close position. Then, the inflow of the fuel into the sac portion101stops, but the fuel left in the sac portion101is continuously injected into the combustion chamber103due to inertial force.

When the fuel has flowed out of the sac portion101, the sac portion101is placed under negative pressure, and a backflow from the combustion chamber103to the sac portion101occurs as illustrated in the illustration (c) inFIG. 1. As a result, the deposit is formed at the injection holes102and their periphery. The deposit blocks the fuel from flowing, which may cause an improper injection amount and an improper injection state of the fuel.

To address such a problem, Patent Document 1 presents various methods that reduce the backflow to the sac portion.

Specifically, Patent Document 1 proposes a method of lifting the needle again such that only the sac portion is filled with the fuel after the fuel injection ends (Method 1), a method of reducing the closing speed of the needle such that the fuel remains in the sac portion at the end of the fuel injection (Method 2), a method of using a special needle including an outer needle and an inner needle (Method 3), and a method of providing an openable/closable valve outside the openings of the injection holes (Method 4).

An injector operating mechanism has many variations. Among them, Patent Document 1 is directed to an injector for diesel engines employing a needle that opens and closes hydraulically (a float needle) (refer to FIG. 2 of Patent Document 1).

Specifically, a needle 214 of the injector 21 is biased in a closing direction by a spring 216. A control chamber 215 is formed on a basal end side of the needle 214, and a sac portion 220 is formed on a distal end side of the needle 214, into both of which high-pressure fuel is introduced. A relief channel 218 discharging the introduced fuel is connected to the control chamber 215. A solenoid valve 219 opens and closes the relief channel 218.

When the solenoid valve 219 is closed, fuel pressure increases in both of the control chamber 215 and the sac portion 220, and no pressure difference is made between the basal end side and distal end side of the needle 214 Thus, the biasing force of the spring 216 moves the needle 214 in the closing direction. On the other hand, when the solenoid valve 219 is opened, the fuel pressure of the control chamber 215 decreases, and the basal end side of the needle 214 becomes lower in pressure than the distal end side thereof. This moves the needle 214 in an opening direction against the biasing force of the spring 216.

That is to say, the injector 21 of Patent Document 1 controls the motion of the needle 214 using the fuel pressure difference obtained through opening and closing the solenoid valve 219.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Technical Problem

Method 1 of Patent Document 1 requires control of the needle motion such that the needle is lifted again after an instructed appropriate amount of fuel is injected and that only the sac portion is filled with the fuel without leaking the fuel to the combustion chamber. However, the volume of the sac portion is small, and ultrafast, high-precision control is required. Moreover, the needle slightly bounces at the moment when the tip end of the needle is seated on a valve seat to be closed. Consequently, in actuality, such needle control is difficult, and the fuel may leak to the combustion chamber to cause a malfunction.

In Method 2, to reduce the closing speed of the needle, the biasing force of the spring needs to be reduced to a certain level For that purpose, opening and closing of the solenoid valve requires adjustment such that constant fuel pressure difference occurs between the basal end side and distal end side of the needle being displaced (while volumes on both sides are changing). Such control is also difficult in actuality.

Methods 3 and 4 involve complicated structure, which may cause another malfunction. Therefore, Methods 3 and 4 are not easy to put into practice.

Further, when the fuel is injected in an intake stroke, fuel injection conditions are set considering a flow within the combustion chamber so that the fuel is sprayed in an optimum state. However, reducing the opening speed of the needle decreases an injection speed. Consequently, the fuel cannot be sprayed in an appropriate state, which may have an influence on fuel economy.

Given these circumstances, an object of the present disclosure is to block a backflow of the fuel into the injector after fuel injection through executing practicable, easy control.

Solution to the Problem

The present disclosure relates to an engine control device including an injector injecting fuel in a combustion chamber within a cylinder.

The injector has a body a tip end portion of which is exposed to the combustion chamber; a sac portion which is a space formed in the tip end portion and into which the fuel flows; an injection hole communicating with the combustion chamber and the sac portion; and a needle slidably disposed within the body to be displaced between a close position where no fuel is allowed to flow into the sac portion and an open position where the fuel is allowed to flow into the sac portion.

The control device includes a fuel injection controller controlling a fuel injection period in accordance with an operating state of the engine, and an injector controller controlling a motion of the needle in accordance with a fuel injection condition set by the fuel injection controller. The injector controller executes slow close control to reduce a moving speed of the needle before the needle reaches the close position when the fuel injection period ends.

That is to say, this control device reduces the moving speed of the needle before the needle reaches the close position when the fuel injection period ends. This allows the needle to be slowly displaced toward the close position, and blocks the sac portion from being placed under negative pressure, thereby leaving the fuel in the sac portion. This also blocks the needle from bouncing.

As a result, a backflow of the fuel from the combustion chamber to the sac portion after fuel injection is reduced, and the deposit is not easily formed at the injection hole and its periphery. Consequently, the fuel can be injected stably over a long term.

In the control device, the slow close control may include executing processing of temporarily stopping the motion of the needle in a period during which the needle is displaced from the open position to the close position.

Temporarily stopping the motion of the needle requires no complicated calculation, and is easily put into practice Since the displacement of the needle is temporarily stopped (the moving speed is substantially zero), the slow close control is executed before the needle reaches the close position.

In the engine control device, the slow close control may include executing processing of setting a speed at which the needle is displaced from the open position to the close position to a predetermined speed, and changing the predetermined speed in accordance with the operating state of the engine.

The speed of the needle is set to the predetermined speed when the needle is at the open position. Thus, the slow close control is executed before the needle reaches the close position. Consequently, even under high-speed control, the motion of the needle is stabilized, and high-precision control can be performed.

In the control device, the operating state of the engine may be the number of revolutions of the engine, and the predetermined speed may be changed to increase with a decrease in the number of revolutions.

In an operating region with the lower number of revolutions of the engine, a weak flow is formed in the combustion chamber. Consequently, when the injection speed of the fuel injected into the combustion chamber decreases, the state of the fuel spray may be affected by the flow. In contrast, such a setting can protect the fuel being sprayed from the adverse effects of the slow close control.

As the injector, an injector driven by current control is preferably used.

That is to say, the injector preferably has: a body a tip end portion of which is exposed to the combustion chamber; a sac portion which is a space formed in the tip end portion and into which the fuel flows; an injection hole communicating with the combustion chamber and the sac portion; a needle slidably disposed within the body to be displaced between a close position where no fuel is allowed to flow into the sac portion and an open position where the fuel is allowed to flow into the sac portion, a spring applying a driving force toward the close position to the needle; and an opening driver applying a driving force toward the open position to the needle upon receiving a current.

The control device includes: a fuel injection controller controlling injection of the fuel in accordance with an operating state of the engine, and an injector controller controlling a current to be supplied to the opening driver in accordance with a fuel injection condition set by the fuel injection controller, and the injector controller supplies an open displacing current for displacing the needle to the open position to the opening driver when a fuel injection period set by the fuel injection controller starts, supplies an open state-holding current for holding the needle at the open position to the opening driver during the injection period, and supplies a speed reduction current for reducing a moving speed of the needle to the opening driver after supply of the open state-holding current is stopped and before the needle reaches the close position when the injection period ends.

Thus, the injector can be operated with good response, and can be stably controlled with high precision even at a high speed on the order of milliseconds.

In that case, the motion of the needle may be temporarily stopped upon receiving the speed reduction current.

In a preferred embodiment, the speed reduction current is larger than the open state-holding current and smaller than the open displacing current.

This enables temporary stop of the needle in a suitable manner, and besides, the just right amount of current can be supplied, which can archive efficient control.

Such slow close control is effective when the fuel is injected in the intake stroke, in which the internal pressure of the combustion chamber is low, rather than in a compression stroke, in which the internal pressure of the combustion chamber is high.

When the injector injects the fuel in the intake stroke, a period during which the motion of the needle is temporarily stopped is preferably shortened with the decrease in the number of revolutions of the engine.

When the motion of the needle is temporarily stopped, the injection speed of the fuel injected into the combustion chamber may decrease at the end of the fuel injection, which may adversely affect the state of the fuel spray. In contrast, such a setting can protect the fuel being sprayed from the adverse effects.

The injector controller may supply the speed reduction current to the opening driver while changing a value of the speed reduction current.

The speed of the needle, even if it is very high, can be freely adjusted through current control, enabling high-precision control.

The speed reduction current may be set smaller than the open displacing current.

This enables reduction of the speed of the needle in a suitable manner, and besides, the just right amount of current can be supplied, which can archive efficient control.

Advantages of the Invention

The disclosed engine control device can practice blocking of a backflow of fuel into an injector after fuel injection. Consequently, the fuel can be injected stably in a combustion chamber over a long term.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the following description is merely exemplary one in nature, and does not limit the present invention, applications, or uses thereof.

First Embodiment

FIG. 2illustrates an engine1disclosed in the present embodiment. This engine1is a multiple cylinder gasoline engine mounted as a power source on an automobile. Although being the gasoline engine, the engine1may use fuel containing gasoline as a main component (e.g., gasoline containing ethyl alcohol).

This engine1mainly includes a cylinder block1a, and a cylinder head1bassembled to the top thereof. The cylinder block1ais provided with a plurality of cylindrical cylinders2(FIG. 2illustrates one of them) arranged side by side in a direction orthogonal to the paper ofFIG. 2. A piston3is inserted into each of the cylinders2to be reciprocable. These pistons3are coupled to a crankshaft5via a connecting rod4.

The crankshaft5rotates in response to the reciprocating motion of these pistons3Power obtained by the rotation of the crankshaft5is outputted via a transmission (not illustrated). The transmission has a mechanism enabling changes of a gear position (e.g., from a first position to a sixth position). The obtained power is transmitted to wheels with the set gear position. The transmission may be an automatic transmission (what is called AT) or a manual transmission (what is called MT). The type of the transmission of this engine1does not matter.

A combustion chamber6whose top and bottom are defined by a lower face of the cylinder head1band an upper face of the piston3, respectively, is formed in an upper portion of the inside of each of the cylinders2. Although not illustrated, a cavity (a recess) guiding a flow of the fuel injected into the combustion chamber6is formed at the upper face of the piston3. An intake inlet of an intake port7and an exhaust outlet of an exhaust port8formed in the cylinder head1bare open in the upper portion of the combustion chamber6. An intake valve9and an exhaust valve10opening and closing the intake inlet and the exhaust outlet, respectively, are provided in the cylinder head1b. The number of the intake valve9and exhaust valve10of the present disclosure does not matter. In this engine1, each of the cylinders2is provided with two intake valves9and two exhaust valves10.

Each of the intake valves9and the exhaust valves10is driven to open and close in conjunction with the rotation of the crankshaft5by valve motion mechanisms11installed in the cylinder head1b. The valve motion mechanism includes various mechanisms, such as one with a lift amount and opening/closing timing of the valve fixed, and one with these parameters made variable. The valve motion mechanisms11are selected as appropriate in accordance with control of the engine1.

The cylinder head1bis provided with a spark plug12and an injector40in each of the cylinders2. The spark plug12has a discharge terminal generating a spark at a tip end thereof. The spark plug12is disposed in the cylinder head1bsuch that the tip end protrudes at a middle portion of the top (a middle portion when viewed in a vertical direction) of the combustion chamber6.

The injector40is a shaft-shaped member injecting the fuel. While the engine1is operating, the fuel is supplied to the injector40at a predetermined fuel pressure through a fuel supply path (not illustrated). The injector40is disposed in the cylinder head1bto extend obliquely downward such that a tip end portion thereof is exposed at a side portion of the top (a side portion viewed in the vertical direction) of the combustion chamber6from an intake side. That is to say, this injector40is what is called a direct-injection injector, which injects the fuel within the combustion chamber6(the details of the structure of the injector40will be described later).

An intake channel14is connected to an inlet of the intake port7opening through one of side faces of the cylinder head1b. Through the intake channel14and the intake port7, outside air (fresh air) is supplied to the combustion chamber6. An exhaust channel15is connected to an outlet of the exhaust port8opening through the other side face of the cylinder head1b. Exhaust gas (combustion gas) generated in the combustion chamber6is exhausted through the exhaust port8and the exhaust channel15.

The intake channel14is provided with an electronically controlled throttle valve16which regulates a flow rate of outside air in accordance with an accelerator position (which changes when a driver presses an accelerator pedal). The opening/closing of the throttle valve16can be controlled independently of the accelerator position.

The exhaust channel15is provided with a catalytic converter17. The catalytic converter17incorporates a three-way catalyst. When the exhaust gas passes through the catalytic converter17, harmful components (NOx, CO, and HC) in the exhaust gas are purified.

Operation of the engine1is integrally controlled mainly by a powertrain control module (PCM)20The PCM20receives various pieces of information constantly inputted from various kinds of sensors in order to detect an operating state of the engine1, for example. Based on the pieces of information, the PCM20controls the operation of the valve motion mechanisms11, the spark plug12, the throttle valve16, and the injector40appropriately in accordance with the operating state of the engine1.

FIG. 3illustrates a block diagram related to the control of the injector40. Various sensors are electrically connected to the PCM20, such as an engine RPM sensor21, a gear position detection sensor22, a vehicle speed sensor23, and an accelerator position sensor24. The engine RPM sensor21detects the number of revolutions of the engine1. The gear position detection sensor22detects a gear position of the transmission. The vehicle speed sensor23detects the speed of the automobile. The accelerator position sensor24detects an accelerator position. While the engine1is operating, pieces of information are constantly inputted to the PCM20from these sensors.

The PCM20sets a target torque in accordance with the operating state of the engine1and an instruction about the output of the engine1. The PCM20outputs the set target torque to an injector ECU30. Specifically, the PCM20determines the state of the number of revolutions of the engine and the state of an engine load based on the pieces of information inputted from these sensors. The PCM20then sets a next target torque from the determined states and the accelerator position, and outputs the next target torque to the injector ECU30.

The injector ECU30is a control device attached to the injector40. The injector ECU30has a function tailored to the control of the injector40. The injector ECU30controls a motion of a needle42, which will be described later, of the injector40based on the target torque and the operating state of the engine1determined by the PCM20. Specifically, the injector ECU30sets a fuel injection amount corresponding to a set value of the target torque (a required injection amount), and performs control to supply a predetermined current to the injector40based on the required injection amount and the operating state of the engine1.

The injector ECU30includes a plurality of maps for control because control is too fast to catch up with by feedback control. These maps include fuel injection patterns corresponding to the engine load and the number of revolutions of the engine. The injector ECU30selects one of the maps corresponding to the operating state of the engine1, and controls the current to be supplied to the injector40such that the fuel is injected in accordance with the injection pattern.

Provision of the injector ECU30enables an independent calculation related to the fuel injection control. This reduces a processing load on the PCM20, and enables fuel injection control at a higher speed and with higher precision.

Thus, the engine1is configured such that cooperation between the PCM20and the injector ECU30controls fuel injection, and the injector ECU30controls the operation of the injector40. That is to say, in this engine1, the PCM20and the injector ECU30correspond to a “control device.” The PCM20and the injector ECU30constitute a “fuel injection controller,” and the injector ECU30constitutes an “injector controller.” Note that the injector ECU30is not essential. The PCM20may have the same function as the injector ECU30, and the PCM20alone may constitute the “fuel injection controller.”

FIG. 4specifically illustrates the structure of the injector40. This injector40is a direct-driven multi-hole injector. The injector40is configured to be driven by electric control. Specifically, the injector40includes a body41, a needle42, a core43, a solenoid coil44, a coil spring45, and a connector46. An opening driver of the present embodiment includes the core43and the solenoid coil44.

The body41is a substantially cylindrical shaft-shaped member. The body41is generally an assembly of a plurality of parts. The body41is attached to the cylinder head1bsuch that a distal end portion thereof is exposed to the combustion chamber6. A basal end portion of the body41is provided with an inlet41athrough which the fuel is introduced, and a basal fuel chamber41bhousing the introduced fuel. A strainer41cremoving foreign objects is disposed between the inlet41aand the basal fuel chamber41b. The distal end portion of the body41is provided with a distal fuel chamber41dwith the connector46inserted into a middle portion of the space inside the body41.

The connector46is a cylindrical part having a shaft hole46apassing through the center thereof. A cylindrical spring stop47is fixed to a basal end portion of the shaft hole46a. The coil spring45is inserted into a distal end portion of the shaft hole46a. The basal end of the coil spring45is supported by the spring stop47.

In the distal fuel chamber41d, the shaft-shaped needle42and the core43fixed to a basal end portion of the needle42are disposed so as to receive the distal end of the coil spring45. The needle42and the core43are slidable with a predetermined lift amount along a center line A of the injector40. The needle42and the core43are biased toward the distal end side by the coil spring45.

An outer peripheral face of the core43is formed to slide along an inner peripheral face of the body41. A magnet43ais embedded in the outer peripheral face of the core43. The distal fuel chamber41dis partitioned into a basal end space and a distal end space by the core43. The core43is formed with a liquid channel43bwhich allows the basal end space and distal end space of the distal fuel chamber41dto communicate with each other.

Consequently, the fuel introduced into the basal fuel chamber41bis also introduced into the distal fuel chamber41dthrough the shaft hole46aand the liquid channel43b. While the engine1is operating, the fuel is supplied to the basal fuel chamber41b, and thus, the basal fuel chamber41band the distal fuel chamber41dare constantly filled with the fuel of a predetermined fuel pressure.

A sac portion48(a space slightly recessed outward) is formed in the distal end portion of the body41, that is, at a distal end of the distal fuel chamber41d. An annular seat portion48ais provided to surround the sac portion48. The tip end of the needle42is brought into pressure contact with the seat portion48a, thereby liquid-sealing the seat portion48a. A plurality of injection holes49is formed at the distal end portion of the body41. The sac portion48communicates with the combustion chamber6via the injection holes49.

The coil spring45applies a driving force to the needle42such that the needle42moves toward a position (close position) where the needle comes into pressure contact with the seat portion48aat its tip end Consequently, unless external force is acted, the sac portion48is blocked from the distal fuel chamber41d, and no fuel flows into the sac portion48.

A solenoid coil44is provided outside the body41so as to face the core43positioned within the body41. Although not shown, a predetermined amount of current is supplied to the solenoid coil44at predetermined timing in accordance with an instruction from the injector ECU30. When the current is supplied to the solenoid coil44, a magnetic field is formed, and a magnetic force acts on the magnet43aof the core43. This magnetic force gives the core43a driving force that causes the core43to slide toward the basal end against an elastic force of the coil spring45. The tip end of the needle42is lifted away from the seat portion48a, and is directed toward a position where the fuel is allowed to flow into the sac portion48(an open position indicated by the dashed-double-dotted curve in the enlarged drawing ofFIG. 4).

That is to say, in this injector40, a predetermined current (a displacing current) is supplied to the solenoid coil44to displace the needle42to the open position by the action of the magnetic force, the fuel then flows into the sac portion48, and the fuel injection starts. Then, a predetermined current (an open state-holding current) is supplied to the solenoid coil44to hold the needle42at the open position, which allows the fuel injection to continue. Then, when the supply of the current to the solenoid coil44is stopped, the needle42is displaced to the close position by the action of the elastic force of the coil spring45, the inflow of the fuel into the sac portion48stops, and the fuel injection ends.

Consequently, with this injector40, supplying the current to the solenoid coil44immediately opens the valve when the fuel injection starts. Then, stopping the supply of the current to the solenoid coil44immediately closes the valve when the fuel injection ends. Consequently, unlike a float injector using fuel pressure difference, the injector40can be controlled with almost no time lag. The injector40can be stably controlled with high precision even at a high speed on the order of milliseconds or higher.

In general, when the needle42is lifted, a force F acting on the needle42can be represented by the following expression (1).
F=k·x+ΔP·S−Mag  (1)

Here, k represents a spring constant of the coil spring45, x represents a lift amount, ΔP represents a fuel pressure difference acting on the core43toward the close position, S represents an area of the core43on which the fuel pressure difference acts, and Mag represents a magnetic force generated by the solenoid coil44.

Unlike a float injector for diesel engines as disclosed by Patent Document 1, the direct-driven injector40for gasoline engines injects the fuel not in the compression stroke, but in the intake stroke. Thus, values k·x and ΔP·S are small. Thus, the injector40can be controlled with a relatively small current, which can reduce battery power consumption.

The following specifically describes fuel injection control with reference to a flowchart inFIG. 5. As illustrated inFIG. 3, the PCM20constantly reads values detected by the various sensors to determine the operating state of the engine1while the automobile is operating (Step S1). The PCM20then sets a target torque for each combustion cycle to bring the engine1into a required operating state (Step S2), and outputs the set target torque to the injector ECU30together with information on the number of revolutions of the engine and the engine load.

Receiving the information on the target torque from the PCM20, the injector ECU30sets a required injection amount and injection timing corresponding thereto (Step S3). The injector ECU30selects a map corresponding to the operating state of the engine1, that is, the number of revolutions of the engine and the engine load at that time, and reads an injection pattern in the map (Step S4). The injector ECU30then performs current control on the injector40such that the required injection amount of the fuel is injected based on the injection pattern (Step S5).

Illustrations (a) to (c) inFIG. 6schematically illustrate an example of the injection pattern in a normal case. The illustration (a) inFIG. 6illustrates a change in the current supplied to the solenoid coil44, the illustration (b) inFIG. 6illustrates a change in the lift amount of the needle42, and the illustration (c) inFIG. 6illustrates a change in the pressure difference of the sac portion48(“the internal pressure of the sac portion48”−“the internal pressure of the combustion chamber6”).

The horizontal axis of each graph indicates time (in the order of millisecond). This engine1injects the fuel in the intake stroke. Depending on the injection pattern, injection may be divided into a plurality of times. In this example, the injection is performed at a time.

The point at which the lift amount is “0” corresponds to the close position, and the point at which the lift amount is the maximum corresponds to the open position. A period from when the needle42leaves the close position to when the needle42returns to the close position again is a fuel injection period set by the PCM20and the injector ECU30(a period during which the fuel is theoretically injected from the injector40to the combustion chamber6). Consequently, part indicated by a trapezoidal area in the illustration (b) inFIG. 6corresponds to the required injection amount.

As described above, this injector40performs current control to open the valve when the fuel injection starts. This can displace the needle42at a high speed, and enables the needle42to be lifted with a slight time lag with respect to the injection pattern. That is to say, the opening of the valve can be controlled with high precision. The valve opening operation requires lifting of the needle42at a high speed against the coil spring45and the fuel pressure. For that purpose, the injector ECU30supplies a relatively large current (the displacing current) to the solenoid coil44.

When the needle42reaches the open position, the injector ECU30supplies a current smaller than the displacing current (the open state-holding current) to the solenoid coil44. This operation holds the needle42at the open position.

When a predetermined period has passed, the injector ECU30stops the supply of the open state-holding current to the solenoid coil44. This triggers the valve closing operation. In the valve closing operation, the current control allows the coil spring45to immediately close the valve. In the valve closing operation, the elastic force of the coil spring45displaces the needle42. Thus, the needle42is displaced at a lower speed than in the valve opening operation (gentler in slope).

When the needle42reaches the close position, the injection period ends, and the fuel injection stops. At that time, the inflow of the fuel into the sac portion48stops. However, as illustrated in an enlarged scale in the illustration (c) inFIG. 6, the fuel in the sac portion48is continuously injected into the combustion chamber6by the action of inertial force. This places the sac portion48under negative pressure.

In the intake stroke, in particular, the internal pressure of the combustion chamber6is low, unlike the compression stroke. For this reason, the fuel easily flows out, and the sac portion48is more easily brought into negative pressure.

Therefore, after the end of the injection period (after the needle42has reached the close position), burned gas (containing carbon) left in the combustion chamber6in the immediately preceding exhaust stroke flows back to the sac portion48, which may generate deposit at the injection holes49and its periphery.

Under these circumstances, this engine1is configured to reduce the possibility that the sac portion48is placed under negative pressure, which can occur after the end of fuel injection. Specifically, using the injector40having good response, the motion of the needle42is temporarily stopped immediately before the needle42reaches the close position in the valve closing operation when the injection period ends.

Specifically, after the supply of the open state-holding current is stopped and the valve closing operation starts, and immediately before the needle42reaches the close position, the injector ECU30supplies a temporary stop current for temporarily stopping the motion of the needle42to the solenoid coil44. The term “temporary stop” referred to in this section designates not only the case where the needle42completely stops its motion, but also the case where the needle42reduces its speed to the extent it stops the motion. To sum up, only required is to give an opposite driving force to the needle42to block the displacement of the needle42such that the sac portion48is not brought into negative pressure. That is to say, the temporary stop control is an example of slow close control which will be described later.

Illustrations (a) to (d) inFIG. 7exemplify an injection pattern when the temporary stop control is performed. The illustration (a) inFIG. 7illustrates a change in the current supplied to the solenoid coil44, the illustration (b) inFIG. 7illustrates a change in the lift amount of the needle42, the illustration (c) inFIG. 7illustrates a change in the pressure difference of the sac portion48, and the illustration (d) inFIG. 7illustrates a change in the fuel amount in the sac portion48.

As illustrated in the illustration (a) inFIG. 7, after the normal injection period ends and the supply of the open state-holding current is stopped, a temporarily stopping current is supplied to the solenoid coil44to temporarily stop the motion of the needle42again. The temporarily stopping current is only required to temporarily stop the needle42, and thus, is preferably set to be a current that is larger than the open state-holding current and is smaller than the displacing current.

Since the sac portion48, which is a minute space, is targeted, the needle42preferably temporarily stops at timing immediately before reaching the close position during the valve closing operation. Supply of the temporarily stopping current to the solenoid coil44blocks the displacement of the needle42, and as illustrated in the illustration (b) inFIG. 7, a small lift amount of the needle42is held immediately before reaching the close position. Consequently, the needle42to be seated on the valve seat is displaced slowly, and as illustrated in illustrations (c) and (d) inFIG. 7, the fuel remains in the sac portion48, blocking the sac portion48from becoming negative in pressure. This also blocks the needle42from bouncing.

As a result, a backflow of the fuel from the combustion chamber6to the sac portion48after fuel injection is reduced, and the deposit is not easily formed at the injection hole49and its periphery. Thus, appropriate fuel injection can be performed stably over a long term. Temporarily stopping the needle42is a simple operation requiring no complicated calculation, and can reduce a processing load on the injector ECU30.

(Influence of Number of Engine Revolutions and Engine Temperature)

When such temporary stop control is performed, an injection speed of the fuel injected into the combustion chamber6may decrease at the end of the fuel injection.

When the fuel is injected in the intake stroke, fuel injection conditions are set so that the fuel is sprayed in an optimum state in order to control a combustion state. For example, the injection timing and the shape of a cavity of the piston3are combined to generate a predetermined flow such as a tumble flow or a swirl flow in the combustion chamber6so as to allow the fuel to be sprayed in the optimum state. Given this situation, when the injection speed of the fuel decreases, the fuel cannot be sprayed in the optimum state, which may have an influence on fuel economy and the like.

In an operating region with a lower number of revolutions of the engine, in particular, the flow formed in the combustion chamber6is weaker than that in an operating region with a higher number of revolutions of the engine. For this reason, the state of the fuel spray is easily influenced by the flow. Given these circumstances, this engine1is configured to reduce a period during which the needle42temporarily stops moving with the decrease in the number of revolutions of the engine.

Specifically, as illustrated inFIG. 8, in the operating region with a higher number of revolutions of the engine, time during which the temporarily stopping current is supplied to the solenoid coil44is set to be longer such that time during which the needle42temporarily stops moving becomes relatively long. In the operating region with a lower number of revolutions of the engine, the time during which the temporarily stopping current is supplied to the solenoid coil44is set to be shorter such that the time during which the needle42temporarily stops relatively reduces.

This can protect the fuel being sprayed from adverse effects of the temporary stop control.

The injector ECU30adjusts the timing at which the open state-holding current is stopped, and the displacement speed of the needle42in the valve closing operation, such that the required injection amount is kept constant without changing the injection period. The injector40, which is electrically controlled, can perform such adjustment.

Similarly, the fuel being sprayed can also be influenced by engine temperature. Specifically, when the engine temperature is low, the fuel sprayed in the combustion chamber6is hard to vaporize. For this reason, when the injection speed of the fuel decreases, the fuel cannot be sprayed in the optimum state, which may have an influence on fuel economy and the like.

Given these circumstances, in a preferred embodiment, the period during which the needle42temporarily stops moving decreases with the decrease in the engine temperature and the number of revolutions of the engine. A possible setting is, for example, switching the length of the period during which the needle42temporarily stops moving before and after completion of what is called warming up for raising the engine temperature to a predetermined temperature after cold startup.

Second Embodiment

A second embodiment exemplifies the case in which the slow close control is performed, i.e., the moving speed of the needle42is lowered so as not to generate negative pressure in the sac portion48, which can occur after the end of fuel injection. The engine1and other components have the same structure as those of the first embodiment. Thus, like reference characters designate identical or corresponding components in the drawings, and description thereof may not be repeated.

The engine1of the second embodiment is configured to reduce the speed of the needle42displaced from the open position to the close position when the injection period ends.

Specifically, when the supply of the open state-holding current is stopped and the valve closing operation starts, the needle42of the first embodiment is displaced toward the close position at a constant speed by the driving force generated by the elasticity of the coil spring. In contrast, in the engine1of the second embodiment, the injector ECU30supplies a speed reduction current for reducing the speed of the needle42to the solenoid coil44.

Illustrations (a) to (d) inFIG. 9exemplify an injection pattern when the slow close control is performed. The illustration (a) inFIG. 9illustrates a change in the current supplied to the solenoid coil44, the illustration (b) inFIG. 9illustrates a change in the lift amount of the needle42, the illustration (c) inFIG. 9illustrates a change in the pressure difference of the sac portion48, and the illustration (d) inFIG. 9illustrates a change in the fuel amount in the sac portion48.

As illustrated in the illustration (a) inFIG. 9, when the normal injection period ends and the supply of the open state-holding current is stopped, the speed reduction current is supplied to the solenoid coil44. The speed reduction current is only required to reduce the speed of the needle42to a predetermined value against the driving force of the coil spring, and thus, is a current smaller than the displacing current. The magnitude of the speed reduction current is adjusted in accordance with a speed reduction amount.

Adjusting the magnitude of the speed reduction current can give an opposite driving force of a desired magnitude against the driving force of the coil spring to the needle. Consequently, the displacement speed of the needle can be freely adjusted. Further, through current control, the adjustment can be made with high precision.

The injector ECU30adjusts the timing at which the open state-holding current is stopped in accordance with the reduced displacement speed such that the required injection amount is made constant. Electric control enables such adjustment. Even when the displacement speed is made variable, the required injection amount can be maintained with high precision.

In a preferred embodiment, the speed reduction current is a constant value. This is because the control is performed at a high speed on the sac portion48, which is a minute space, making the speed reduction current variable during closing of the valve complicates the control, increasing a processing load. When the speed reduction current is a constant value, the motion of the needle is stabilized, and the control can be performed with higher precision.

Thus, the needle is displaced at a constant displacement speed which is made lower than a displacement speed under the driving force generated by the coil spring alone, which is indicated by a virtual line in the illustration (b) inFIG. 9. Consequently, the needle42is slowly displaced to be seated on the valve seat, and the fuel remains in the sac portion48. This can block the sac portion48from being placed under negative pressure as illustrated in the illustrations (c) and (d) inFIG. 9. This also blocks the needle42from bouncing.

As a result, a backflow of the fuel from the combustion chamber6to the sac portion48after the fuel injection is reduced, and the deposit is not easily formed at the injection holes49and their periphery. Thus, appropriate fuel injection can be performed stably over a long term. Reducing the speed of the needle42is a simple operation requiring no complicated calculation, and can reduce a processing load on the injector ECU30.

(Influence of Operating State of Engine)

When such slow close control is performed, an injection speed of the fuel injected into the combustion chamber6may decrease at the end of the fuel injection, just like when the temporary stop control is performed. When the injection speed of the fuel decreases, the fuel cannot be sprayed in the optimum state, which may have an influence on fuel economy and the like. In the operating region with a lower number of revolutions of the engine, the state of the fuel spray is easily influenced by the flow.

Given these circumstances, the engine1of the second embodiment is configured to increase the displacement speed of the needle42with the decrease in the number of revolutions of the engine.

Specifically, as illustrated inFIG. 10, in the operating region with a higher number of revolutions of the engine, the value of the speed reduction current supplied to the solenoid coil44is set to be larger such that the displacement speed of the needle42relatively decreases (gentler in slope). In the operating region with a lower number of revolutions of the engine, the value of the speed reduction current supplied to the solenoid coil44is set to be smaller such that the displacement speed of the needle42relatively increases (steeper in slope).

This can protect the fuel being sprayed from adverse effects of the slow close control.

In the engine1of the second embodiment, just like in the engine1of the first embodiment, the fuel cannot be sprayed in the optimum state when the injection speed of the fuel decreases at low engine temperature, which may have an influence on fuel economy and the like.

Thus, in a preferred embodiment, the engine1of the second embodiment is configured to relatively increase the displacement speed of the needle42with the decrease in the engine temperature and the number of revolutions of the engine. A possible setting is, for example, switching the magnitude of the displacement speed of the needle42before and after completion of what is called warming up for raising the engine temperature to a predetermined temperature after cold startup.

The engine control device is not limited to those described in the above embodiments, and may include various other configurations.

Although the embodiments have taken a gasoline engine performing fuel injection in the intake stroke as an example, the present invention can also be applied to diesel engines performing fuel injection in the compression stroke.

The number of stops in the temporary stop control is not limited to one. The temporary stop control may be performed a plurality of times during the valve closing operation.

When the fuel injection is divided in a plurality of times, the temporary stop control and the slow close control are preferably performed only in the last fuel injection.

In the engine1of the second embodiment, the displacement speed of the needle42can be decreased and increased Current control enables such decrease and increase.

DESCRIPTION OF REFERENCE CHARACTERS