JPH116466A - In-cylinder injection type internal combustion engine - Google Patents

Abstract

(57) [Problem] To stabilize stratified charge ultra-lean combustion operation of a direct injection engine by simple control. SOLUTION: During stratified combustion operation of an engine, an electromagnetic proportional pressure control valve (64) is drive-controlled so that the fuel pressure increases as the intake air temperature rises, and the fuel is injected from an injection valve (4) into a combustion chamber of the engine. The fuel transport speed is kept constant irrespective of the intake air temperature, the timing of forming the stratified mixture around the spark plug is optimized, and the optimum stratified combustion is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection internal combustion engine, and more particularly, to a direct injection internal combustion engine in which the fuel pressure is changed according to the intake air temperature.

[0002]

[Related Background Art] It is known that a fuel-injection spark ignition type internal combustion engine for a vehicle is operated with a lean mixture at a low load in order to reduce harmful exhaust gas components and improve fuel efficiency. In order to ensure the above, there is a limit to lean air-fuel mixture in an intake pipe injection type internal combustion engine. Therefore, in order to further reduce fuel consumption, a direct injection internal combustion engine in which fuel is directly injected into a combustion chamber has been proposed.

In a direct injection type internal combustion engine, fuel is injected during an intake stroke during a high load operation to uniformly generate a stoichiometric air-fuel ratio or a rich air-fuel ratio in the cylinder to obtain a high output while obtaining a low output. In the load operation range, fuel is injected from the fuel injection valve during the compression stroke toward the cavity provided at the top of the piston to form a stratified mixture with an air-fuel ratio close to the stoichiometric air-fuel ratio around the ignition plug at the ignition timing. In addition, the operation at an extremely lean air-fuel ratio in the entire cylinder is stably performed.

[0004] The stratified charge ultra-lean combustion (hereinafter referred to as stratified combustion) starting from fuel injection in the compression stroke is performed by injecting fuel from a combustion injection valve, generating fuel spray by atomizing fuel, and suction air flow. Transport of fuel spray around the spark plug through the cavity, formation of a stratified mixture around the spark plug, and combustion of the mixture initiated by the ignition operation of the spark plug. It occurs sequentially as time passes. The quality of the stratified combustion mainly depends on the appropriateness of the fuel injection timing and the ignition timing. Therefore, in the stratified combustion operation, these time parameters are set so as to fall within a time parameter region (hereinafter, referred to as a stable combustion region) capable of achieving stable stratified combustion, and the injection valve and the ignition plug are set at the set timing. To obtain a good stratified combustion state.

It should be noted that, in addition to the time parameters described above, the transport speed of the fuel spray contributes to stratified combustion. The transport speed changes mainly in accordance with the fuel injection pressure and the intake air temperature. In a predetermined fuel injection pressure region, the transport speed decreases as the intake air temperature increases. In this case, the higher the intake air temperature, the longer the time required from the time of fuel injection to the formation of the stratified mixture. In this way, the state of formation of the air-fuel mixture depends on the intake air temperature, and therefore, the preferred value of the time parameter changes according to the intake air temperature.

Therefore, in order to achieve low fuel consumption and high output by stratified combustion, it is conceivable to adopt a control method of setting a time parameter region (stable combustion region) for the stratified combustion operation control for each intake air temperature. In this case, at the time of the stratified combustion operation, for example, a time parameter region suitable for the actual intake air temperature is selected, and an optimal time for entering the selected parameter region and conforming to the engine operation state (rotational speed, load). Find the parameter value (optimal time),
Each of the injection valve and the spark plug will be operated at the optimal time.

However, a stable combustion region for each intake air temperature is set in advance.
A great deal of labor is required to create a look-up table in advance for each stable combustion region to determine the optimum value suitable for the operating state of the engine. In addition, according to such a control method, there is a problem that a control procedure becomes complicated, and new requirements such as an increase in a memory capacity with respect to hardware requirements arise.

Therefore, in consideration of the fact that the preferred range of the time parameter for obtaining stable stratified combustion is generally narrowed as the intake air temperature becomes higher, the time parameter region is adjusted so as to be adapted to a higher intake air temperature. It is set narrow in advance so as to cope with a change in intake air temperature during stratified combustion operation. However, in this case, as the actual intake air temperature deviates from the intake air temperature assumed in setting the time parameter area, the actual fuel spray transport speed deviates from that assumed for control, so that the stratified mixture is optimally formed. Otherwise, optimal stratified combustion may not be achieved.

If the time parameter region is set narrow in advance in consideration of the intake air temperature change, the engine operation range in which the stratified combustion operation can be performed is also narrowed accordingly. As a result, the fuel consumption, the exhaust emission, and the like by the stratified combustion operation are reduced. Will be limited. In addition, for the direct injection type internal combustion engine, a lean combustion operation mode other than the compression stroke injection mode may be set, but when the time parameter region is set narrow in consideration of the intake air temperature change, such an operation mode is set. The lean combustion operation range corresponding to the above also tends to be narrow.

[0010]

SUMMARY OF THE INVENTION According to the present invention, it is possible to further stabilize and optimize lean combustion including stratified charge ultra-lean combustion by relatively simple control, and to further improve fuel economy and exhaust emission. It is an object of the present invention to provide an in-cylinder injection type internal combustion engine capable of achieving some improvement.

[0011]

According to the present invention, there is provided an in-cylinder injection type internal combustion engine which performs stratified combustion by collecting fuel directly injected from an injection valve into a combustion chamber in a specific operation range near an ignition plug. Provided. In the in-cylinder injection internal combustion engine according to claim 1, the operation of the fuel pressure adjusting means is controlled by the control means in accordance with the intake air temperature at least while the internal combustion engine is operating in the specific operating range, whereby The fuel pressure is adjusted according to the intake air temperature. Here, the pressure at which fuel is injected from the injector into the combustion chamber (fuel injection pressure) is determined mainly by the fuel pressure (fuel supply pressure to the injector) acting on the injector. Also, the fuel injected into the combustion chamber and atomized is
The fuel is transported to the vicinity of the spark plug at a transport speed determined mainly by the fuel injection pressure and the intake air temperature. In the internal combustion engine of the present invention, the fuel pressure (fuel injection pressure) and, consequently, the fuel spray transport speed are variably adjusted according to the intake air temperature. Therefore, for example, to offset the change in the fuel spray transport speed due to the change in the intake air temperature,
The fuel spray transport speed can be adjusted by adjusting the fuel pressure, so that an optimum fuel spray transport speed and thus an optimum stratified combustion can be obtained independently of the intake air temperature.

The operation of a direct injection internal combustion engine is typically controlled based on time parameters such as a fuel injection period (fuel injection start / end timing) and ignition timing. In order to obtain stable stratified combustion in this type of internal combustion engine, it is necessary to collect the fuel injected and atomized over the fuel injection period near the spark plug at the ignition timing to form a stratified mixture. According to the present invention, the influence of the change in the intake air temperature on the fuel spray transport speed can be eliminated or reduced by adjusting the fuel pressure, and the fuel spray transport speed can be made constant regardless of the intake air temperature.
As a result, the above-described essential conditions for obtaining stable stratified combustion are satisfied irrespective of the intake air temperature, and the stratified combustion is stably performed.

From the viewpoint of improving fuel efficiency and exhaust emissions, it is desirable that the ratio of the stratified combustion operation region (more generally, the lean combustion operation region) to the entire operation region of the internal combustion engine is large. In the conventional method, in consideration of the influence of the intake air temperature change on obtaining stable stratified combustion, the time parameter region and, consequently, the stratified combustion operation region must be narrowed. On the other hand, according to the present invention in which the influence of the intake air temperature change is removed or reduced, the time parameter region in which the stratified combustion can be stably performed, that is, the stratified combustion operation region is substantially widened, and the fuel consumption and the exhaust emission are improved.
Further, it is not necessary to perform a matching operation such as presetting a time parameter area for each intake air temperature, and the control procedure is simpler than in a case where stratified combustion operation control is performed using a different time parameter area for each intake air temperature. And hardware requirements are reduced.

In the cylinder injection type internal combustion engine according to the first aspect, during operation of the engine in an operation range other than the specific operation range,
In the case of an engine in which fuel injected from the injection valve into the combustion chamber is uniformly diffused into the combustion chamber to perform premixed combustion, at the time of the premixed combustion, the operation of the fuel pressure adjusting means by the control means to simplify the control. Preferably, no control is performed. Even if the diffusion speed of the fuel spray changes with a change in the intake air temperature, the premixed combustion is normally performed stably, so that there is no problem by omitting the fuel pressure control.

Preferably, the fuel pressure adjusting means is operated so as to change the fuel pressure within a range of about 3 to 7 MPa. This is because when the fuel pressure changes in a range that is considerably wider than such a fuel pressure change range, factors other than the intake air temperature greatly affect the spraying, and the fuel spray transport speed does not always increase simply as the fuel pressure increases. . That is, if the fuel pressure is lower than about 3 MPa, the splitting (atomization) of the fuel spray discharged from the injection valve due to the drag of the air becomes dominant, and if the fuel pressure is higher than about 7 MPa, the atomization of the fuel spray by the injection pressure takes place. Becomes dominant, so that the simple tendency that the fuel spray transport speed decreases as the intake air temperature rises cannot be obtained unless the fuel pressure is within the above-mentioned fuel pressure change range.
Therefore, the fuel pressure change range of the fuel pressure adjusting means is approximately 3 to 7 MPa.
By doing so, simple fuel pressure control in consideration of the intake air temperature can be realized, stratified combustion can be stabilized, and requirements imposed on pumps, injection valves, and the like for generating fuel pressure are alleviated.

According to the second aspect of the present invention, the operation of the fuel pressure adjusting means is controlled by the control means such that the fuel pressure becomes higher as the intake air temperature detected by the intake air temperature detecting means becomes higher. It is characterized by the following. The fuel spray transport speed typically decreases with increasing intake air temperature. Further, the time parameter region in which stable stratified combustion is established narrows as the intake air temperature increases. In the preferred embodiment described above, the fuel pressure increases as the intake air temperature increases, so that the fuel spray transport speed can be increased so as to offset the decrease in transport speed due to the increase in intake air temperature. Therefore, the fuel spray transport speed can be made constant regardless of the intake air temperature, and the stratified combustion can be stabilized.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A direct injection internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings. FIG.
In the figure, reference numeral 1 indicates an in-cylinder injection type in-line 4-cylinder gasoline engine. The engine 1 has a cylinder head 2 on which a spark plug 3 for each cylinder is mounted. The fuel injection valve 4 of each cylinder is disposed inside an injection valve mounting hole opened on the lower surface of the cylinder head 2, and is configured to directly inject fuel into the combustion chamber 5. A hemispherical cavity 8 is formed on the top surface of a piston 7 arranged in the cylinder 6. The intake and exhaust camshafts 11 and 12 for driving the intake and exhaust valves 9 and 10 are rotatably supported above the cylinder head 2. The intake port 13 is formed substantially upright on the cylinder head 2 and extends between the camshafts 11 and 12. A large-diameter EGR port 15 branches obliquely from an exhaust port 14 formed in a substantially horizontal direction.

Reference numeral 16 denotes a coolant temperature sensor for detecting a cooling water temperature, and reference numeral 17 denotes a crank angle sensor that outputs a crank angle signal at a predetermined crank position of each cylinder. The crank angle sensor 17 also functions as an engine speed sensor. Reference numeral 19 denotes an ignition coil for applying a high voltage to the ignition plug 3. The camshaft is provided with a cylinder discrimination sensor (not shown) that outputs a cylinder discrimination signal.

An intake pipe 25 connected to the intake port 13 via an intake manifold 21 having a surge tank 20
Has an air cleaner 22 and a throttle body 23, and a throttle valve 28 is provided in the throttle body 23.
Is provided. An air bypass passage extending around the throttle valve 28 is formed in the intake pipe 25, and a first air bypass valve (ABV) 24 is provided in the middle of the air bypass passage. Further, an intake air temperature sensor 31 and an air flow sensor 32 are attached to the intake pipe 25.

The large-diameter air bypass pipe 26 has both ends connected to the intake pipe 25 on the upstream and downstream sides of the throttle body 23.
The amount of air supplied to the intake manifold 21 through the second ABV 27 is adjusted by a second ABV 27 provided in the middle of the pipe 26. Reference numerals 29 and 30 denote a throttle position sensor for detecting a throttle opening and an idle switch for detecting a throttle fully closed state, respectively.

The exhaust port 14 is connected to an exhaust pipe 43 provided with a three-way catalyst 42 via an exhaust manifold 41 on which an O2 sensor 40 is mounted. The above-mentioned EGR port 15 is connected to the intake manifold 21 via a large-diameter EGR pipe 44, and the EGR port
An R valve 45 is provided. Referring to FIG. 2, the fuel system of the engine 1 includes a fuel tank 50 and an electric low-pressure fuel pump 51 that pumps fuel in the fuel tank. The low-pressure fuel pump 51 pumps fuel to the high-pressure fuel pump 56 by the low-pressure feed pipe 152 via the check valve 52, the filter 53, and the damper 55. A first return pipe 153 branches from the low-pressure feed pipe 152, and the low-pressure feed pipe 1
A low-pressure fuel pressure regulator 54 for adjusting the fuel pressure in 52 is interposed in the return pipe 153. The low-pressure fuel pump 51 operates when the cranking of the engine 1 is turned on, and supplies the low-pressure fuel to the low-pressure feed pipe 15.
2 and to the injection valve 4 via a pipe system described later.

The high pressure fuel pump 56 has a fuel suction port
The low pressure feed pipe 152 is connected downstream of the damper 55. The high-pressure fuel pump 56 is, for example, a single-cylinder pump having a reciprocating plunger drivingly connected to an exhaust-side camshaft, and is driven by the engine 1 to generate a discharge pressure of about 3 to 7 MPa. The discharge port of the high-pressure fuel pump 56 is connected to the high-pressure feed pipe 155. Branch pipe 154
The upstream end is connected to the low pressure feed pipe 152 between the damper 55 interposed in the low pressure feed pipe 152 and the suction port of the high pressure fuel pump 56, and extends around the high pressure fuel pump 56. . This branch pipe 154
A check valve 58 is provided in the middle of
The downstream end of 4 is connected to a high-pressure feed pipe 155. High pressure feed pipe 155 and branch pipe 154
Upstream of the junction with the high pressure feed pipe 15
5 is provided with a check valve 57.

In the pump system having this configuration, the high-pressure fuel pump 56 cannot obtain a sufficient discharge pressure until the rotation speed of the engine 1 increases, so that the check valve 58 is opened and the low-pressure fuel pump 51 Low-pressure fuel is supplied to the low-pressure feed pipe 15
2 and to the injection valve 4 via the branch pipe 154. On the other hand, when the engine speed increases and the fuel discharge pressure from the high-pressure fuel pump 56 exceeds the fuel pressure from the low-pressure fuel pump 51, the check valve 57 opens and the check valve 5
8 is closed, high-pressure fuel is supplied from the high-pressure fuel pump 56 to the injection valve 4 via the high-pressure feed pipe 155.

To further explain the structure of the fuel system, the high-pressure feed pipe 155 has a buffer vessel 5 downstream of the junction of the branch pipe 154 and the high-pressure feed pipe 155.
9 are interposed. The buffer container 59 is formed by widening the high-pressure feed pipe 155, and a resonator 60 communicates with the buffer container 59. Reference numeral 61 denotes a delivery pipe connected to the high-pressure feed pipe 155, and the delivery pipe 61 is provided with the fuel injection valve 4 of each cylinder. A second return pipe 158 extending from the delivery pipe 61 has a fuel pressure sensor 62.
And the resonator 63 communicate with each other. In the middle of the second return pipe 158, the electromagnetic proportional pressure control valve 64
Is provided.

In such a configuration, the high-pressure fuel pump 5
When the plunger of No. 6 reciprocates and suction of low-pressure fuel and discharge of pressurized fuel are performed alternately, pressure waves of high-pressure fuel discharged from the pump 56 flow from the high-pressure feed pipe 155 to the delivery pipe 61. It propagates and is reflected at an obstruction downstream of the delivery pipe, for example at a proportional pressure control valve 64. This reflected wave causes resonance in the fuel passage (part of the high-pressure feed pipe 155, the delivery valve 61, and the second return pipe 158) extending between the discharge port of the pump 56 and the input port of the control valve 64. Become.
In the fuel system shown in FIG. 2, the amplitude of the reflected wave is reduced by the buffer container 59, and the resonance is suppressed by the resonators 60 and 63. Further, pulsation of fuel may occur in the low-pressure feed pipe 152 connected to the high-pressure fuel pump 56 in accordance with the driving of the high-pressure fuel pump 56. In the fuel system shown in FIG.
5 suppresses such pulsation.

As described above, the fuel pressure sensor 62 is provided downstream of the delivery pipe 61, and the fuel pressure in the delivery pipe 61 is detected by the fuel pressure sensor 62. Further, the electromagnetic proportional pressure control valve 64 is provided downstream of the delivery pipe. The control valve 64 is connected to the delivery pipe 61 in accordance with the drive current supplied thereto.
The fuel pressure (fuel injection pressure) acting on the injection valve 4 is variably adjusted. Reference numeral 161
From the high pressure fuel pump 56 to the first return pipe 153
Represents a third return pipe extending to the fuel tank side of
The downstream end of the second return 158 is connected to the return pipe 161. The fuel supplied from the low-pressure fuel pump 51 to the high-pressure fuel pump 56 and used for lubrication and cooling of the pump 56 is returned to the fuel tank 50 via the third return pipe 161 and the first return pipe 153.

An electronic control unit (ECU) indicated by reference numeral 70 in FIGS. 1 and 2 controls the overall operation of the engine 1, and includes an input / output device, a storage device, and a central processing unit. , A timer counter and the like (both not shown). The ECU 70 determines a fuel injection mode, a fuel injection amount, an ignition timing, an EGR gas introduction amount, a fuel injection pressure, etc., based on engine operating state detection information from various sensors connected to the input side thereof. , Ignition coil 19, EGR valve 45, low-pressure fuel pump 5
1. The drive of the proportional pressure control valve 64 and the like is controlled. In connection with the present invention, the ECU 70 has a function of an operation state determination unit 71 that determines an engine operation state based on detection information from various sensors including the intake air temperature sensor 31;
The function of the injection mode selection means 72 for selecting the fuel injection mode in accordance with the determined engine operating state is provided (see FIG. 2). The injection mode selection means 72 of this embodiment sets one of the five injection modes shown in FIG. 3, that is, the air-fuel ratio to rich or stoichiometric in order to obtain an output, based on the rotation speed and the average effective pressure of the engine 1. Open loop mode with premixed combustion, stoichiometric feedback mode, mainly in early injection lean mode in which fuel is injected during the intake stroke and premixed lean combustion is performed, and late in which fuel is injected during the compression stroke and stratified combustion is mainly performed The injection lean mode or the fuel cut mode is selected.

When the late injection lean mode is selected, the ECU 70 sets a fuel pressure setting means 7 for setting a fuel pressure suitable for the intake air temperature detected by the intake air temperature sensor 31.
3 functions. As described below, the fuel pressure setting means 73 preferably sets the fuel pressure to a larger value as the intake air temperature increases, and reduces the decrease in the fuel spray transport speed due to the increase in the intake air temperature by the increase in the transport speed due to the increase in the fuel pressure. And makes the fuel spray transport speed constant regardless of the intake air temperature. Then, the fuel pressure setting means 73 supplies a drive current having a magnitude corresponding to the target value of the fuel pressure set as described above to the electromagnetic proportional pressure control valve 64. In response to this drive current supply, the pressure control valve 64
Operates so that the fuel pressure in the delivery pipe 61 becomes the target fuel pressure. That is, the pressure control valve 64 functions as fuel pressure adjusting means, and the ECU 70 including the fuel pressure setting means 73
It functions as control means for controlling the operation of the fuel pressure adjusting means.

During the stratified combustion, the fuel injected from the fuel injection valve 4 is atomized in the combustion chamber to become a fuel spray, and is transported to the cavity on the top surface of the piston by the intake air flow. When the fuel is injected at an injection pressure of about 3 to 7 MPa, the reaching distance (transport speed) of the fuel spray becomes smaller as the intake air temperature becomes higher at the same fuel injection pressure. That is, the intake air temperature T
If the time change of the fuel spray reaching distance at a is as represented by the solid line in FIG. 5, the intake air temperature Tb (> T
That in a) is shown by the two-dot chain line in FIG. As described above, as the intake air temperature rises, the fuel spray transport speed decreases, and the formation of a stratified mixture is delayed. Therefore, the intake air temperature Ta
In this case, if the preferred range (stable combustion region) of the fuel injection end timing / ignition timing is represented by the elliptical region Ra shaded in FIG. 4, stable combustion at the intake air temperature Tb (> Ta) The region is as shown by the elliptical region Rb. In addition,
The region Ra includes the entire region Rb. As described above, in the conventional control method, a stable stratified combustion is obtained even when the intake air temperature changes, for example, between Ta and Tb.
Is fixedly set as a stable combustion region.

In the present embodiment, if the intake air temperature is the same, attention is paid to the fact that the fuel spray reaching distance is increased as shown in FIG. 6 by increasing the fuel injection pressure. When the fuel injection pressure rises, the fuel injection pressure is increased from the pressure Pa to Pb so that the fuel spray arrival distance increases by an amount corresponding to the decrease in the fuel spray arrival distance due to the rise in the intake air temperature. In this case, even if the intake air temperature rises to Tb in FIG. 5, the fuel spray reach distance can be maintained substantially constant regardless of the intake air temperature change. In other words, the fuel spray reaching distance change curve can be maintained as shown by the solid line in FIG. 5, and therefore, the stable combustion region can be maintained at the same width as the region Ra in FIG. In other words, the latter-stage injection lean mode operation range shown in FIG. 3 can be expanded as compared with the case of the conventional method, and the advantages such as improved fuel efficiency by the stratified combustion operation can be more enjoyed.

Referring again to FIG. 2, the ECU 70 performs the injection according to the fuel pressure detected by the fuel pressure sensor 62, the engine operating state determined by the operating state determining means 71, and the fuel injection mode selected by the injection mode selecting means 72. Controlling the valve opening time (injection start / end timing) of the valve 4;
In addition, an injection amount for controlling the operation timing (ignition timing) of the ignition coil 19 according to the engine operating state and the injection mode.
It functions as ignition timing control means 74.

Hereinafter, the operation control of the engine 1 by the ECU 70 will be described. When the ignition key is operated to the ON position when the engine 1 is in a cold state, the low-pressure fuel pump 51 is turned on, and low-fuel pressure fuel is supplied to the fuel injection valve 4. Next, when the ignition key is operated to the start position, the engine 1 is cranked, and the ECU 70 starts the fuel injection control shown in FIG. In the injection control routine of FIG. 7, the operating state of the engine is determined by the operating state determining means 71 based on the detection information from the various sensors (step S1). The mode is selected (Step S2). During cranking of the engine, the first-stage injection lean mode is selected. Next, it is determined whether or not the selected injection mode is the late injection lean mode (step S3). If the result of this determination is negative, the control flow proceeds from step S3 to step S7 to control the injection valve 4. During the cranking of the engine, the fuel injection control is performed so that the air-fuel ratio becomes relatively rich while the second ABV 27 is substantially fully closed. In this case, the fuel injection from the injection valve 4 into the combustion chamber 5 is performed during the intake stroke, and the injected fuel is uniformly diffused into the combustion chamber by the intake flow to perform premix combustion. At the time of the premix combustion, the fuel pressure adjustment (steps S4 to S6) according to the intake air temperature is not performed, thereby simplifying the control.

When the idle operation of the engine 1 is started, high-pressure fuel is supplied from the high-pressure fuel pump 56 to the fuel injection valve 4. Until the cooling water temperature rises to a predetermined value, the first-stage injection mode is selected. Accordingly, the result of the determination in step S3 in FIG. 7 is negative, and the process proceeds to step S7 without performing the fuel pressure adjustment, and the fuel injection control is performed. At this time, in consideration of the fuel pressure in the delivery pipe 61 detected by the fuel pressure sensor 62, the valve opening time of the fuel injection valve 4 is determined according to the required fuel injection amount, and the fuel injection is performed so as to achieve a rich air-fuel ratio. Will be The idling speed control according to the load of the accessories is performed by adjusting the opening of the first ABV 24. Thereafter, when the O2 sensor 40 is activated, the air-fuel ratio feedback control according to the O2 sensor output voltage is started, and the harmful exhaust gas component is reduced to the three-way catalyst 42.
Purified by

When the warm-up of the engine 1 is completed, the fuel injection is performed in accordance with the fuel injection control area retrieved from the fuel injection control map shown in FIG. 3 based on the target average effective pressure obtained from the throttle opening and the engine speed. The mode is determined. Further, a target air-fuel ratio and a target ignition timing in this fuel injection mode are determined. Then, the drive of the fuel injection valve 4 is controlled in accordance with the fuel injection amount determined based on the target air-fuel ratio. Further, the drive of the ignition coil 19 is controlled according to the target ignition timing. Opening / closing control of the first ABV 24, the second ABV 27, and the EGR valve 45 is also performed.

More specifically, in a low load range such as during idling or low-speed running, the fuel injection control range is the late injection lean range in FIG. In this case, the late injection lean mode is selected. As a result, the determination result in step S3 of FIG. 7 becomes positive, and the fuel pressure setting
Is read from the memory (step S)
4) Next, referring to the intake air temperature / target fuel pressure map illustrated in FIG. 8, the target fuel pressure is determined based on the intake air temperature read in step S4 (step S5). The target fuel pressure is set to increase as the intake air temperature increases. Further, a drive current corresponding to the target fuel pressure is determined by the fuel pressure setting means 73 with reference to a target fuel pressure / drive current map (not shown), and this drive current is applied to the electromagnetic proportional pressure control valve 64 (step S6). Pressure control valve 64
Controls the fuel pressure in an open loop such that the fuel pressure in the delivery pipe 61 becomes the target fuel pressure in accordance with the drive current supply. As a result, the fuel pressure is increased or decreased according to the increase or decrease of the intake air temperature,
As a result, the transport speed of the fuel injected and atomized from the injection valve 4 into the combustion chamber 5 becomes substantially constant regardless of the intake air temperature.

In the next step S7, under the control of the injection amount / ignition timing control means 74, the fuel injection valve 4 and the first fuel injection valve 4 are controlled to have a lean average air-fuel ratio (for example, about 30 to 40).
The drive of the ABV 24 and the second ABV 27 is controlled, the target ignition timing is set based on the target average effective pressure and the engine speed, and the ignition coil 19 operates at the target ignition timing.

In the in-cylinder injection type engine 1, since the intake air flowing from the intake port 13 forms a reverse tumble flow in the cavity 8, the mixture of the fuel injected from the fuel injection valve 4 and the intake air ( (Fuel spray) is collected in the vicinity of the ignition plug 3, and at the time of ignition, an air-fuel mixture close to the stoichiometric air-fuel ratio is formed in a layer around the ignition plug 3, so that good ignitability is ensured even at a lean air-fuel ratio as a whole. Is done. Moreover, as a result of the fuel pressure adjustment in step S6, the fuel spray transport speed is made substantially constant irrespective of the intake air temperature, so that the above-mentioned stable combustion region is also kept substantially constant, and a stratified mixture is formed at an optimal timing. For this reason, by opening the injection valve 4 from the set injection start timing to the set injection end timing and operating the ignition plug 3 at the set ignition timing, optimal stratified combustion can be performed as intended. Therefore, the emission of CO and HC is suppressed to an extremely small amount, and the fuel efficiency is greatly improved.

Further, since the optimum stratified combustion can be achieved by adjusting the fuel pressure even when the intake air temperature increases or decreases, the latter-stage injection lean operation can be performed in comparison with the conventional control method in which the fuel pressure is not adjusted according to the intake air temperature. The mode operation range can be expanded, and the above-described advantages of the stratified combustion operation can be achieved in a wide operation range. Further, the idle speed control is performed by increasing or decreasing the fuel injection amount, and the control response is also very good. Further, in this control region, a large amount of EGR gas can be introduced into the combustion chamber 5, and NOx can be significantly reduced.

In the middle load region such as when the vehicle is traveling at a constant speed, the region is the first-stage injection lean region or the stoichiometric feedback region in FIG. In this case, the fuel injection control of step S7 is performed without performing steps S4 to S6 related to the fuel pressure adjustment. In the lean injection region, the air-fuel ratio is relatively lean (for example,
The fuel injection amount is set so as to be about 20 to 23). The EGR valve 45 is closed. Further, a target ignition timing is set based on the volume efficiency and the engine rotation speed obtained based on the information from the air flow sensor 32, and the ignition coil 19 operates at the target ignition timing.

In the stoichiometric feedback range, the first A
While the BV 24 is controlled, the second ABV 27 is fully closed. Then, while controlling the opening and closing of the EGR valve 45, the O2
Air-fuel ratio feedback control is performed according to the output voltage of the sensor 40. Further, an appropriate amount of EGR gas is introduced into the combustion chamber 5, so that NOx is reduced and fuel efficiency is improved. In a high load region such as during rapid acceleration or high-speed running, an open loop control region shown in FIG. 3 is set, and the first injection mode is selected. In this case, the process proceeds to the fuel injection control without performing the fuel pressure adjustment, and the fuel injection is performed so as to obtain a relatively rich air-fuel ratio while closing the second ABV 27. During the coasting operation during middle-high speed traveling, the fuel cut region in FIG. 3 is reached, and the fuel injection is stopped. Also in this case, no fuel adjustment is performed.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the embodiment, by applying a drive current corresponding to the target fuel pressure from the electronic control unit 70 to the control valve 64, the electromagnetic proportional pressure control valve 64 as the fuel pressure adjusting means is opened-loop controlled to perform the fuel pressure adjustment. However, the fuel pressure may be feedback-controlled to the target fuel pressure based on the actual fuel pressure detected by the fuel pressure sensor 62 and the target fuel pressure.

Further, instead of the electromagnetic proportional pressure control valve 64,
Various fuel pressure adjusting means can be used. For example, a duty control solenoid valve is provided downstream of the delivery pipe 61 so that the fuel pressure in the delivery pipe becomes the target fuel pressure.
The valve opening duty ratio of the duty control solenoid valve may be controlled by an electronic control unit. Alternatively, a spring for pressing the needle of the fuel pressure regulator may be made of bimetal, and this regulator may be attached to the intake pipe. According to this configuration, the intake pipe peripheral wall temperature equivalent to the intake air temperature is transmitted to the bimetal spring of the regulator, and the spring constant of the spring changes according to the intake air temperature change. As a result, the spring pressing force applied to the needle corresponds to the intake air temperature, and the fuel pressure reflects the intake air temperature. According to such a configuration, the functions of the intake air temperature sensor and the fuel pressure sensor are exhibited by the fuel pressure adjusting means itself, so that the device configuration is simplified.

In the above embodiment, a fuel system including a single-cylinder pump having a reciprocating plunger, a check valve, a buffer vessel, a resonator, and the like disposed around the pump is used. Instead, for example, a fuel system using a swash plate pump or removing a buffer container and a resonator can also be used. In the above embodiment, the change in the fuel spray transport speed due to the change in the intake air temperature is offset by the change in the transport speed due to the fuel pressure adjustment so that the transport speed is kept constant regardless of the intake air temperature. It is not essential to adjust the fuel pressure so that the fuel pressure becomes constant, and even if the fuel pressure is adjusted so as to change the fuel spray transport speed according to the intake air temperature within the transport speed range that establishes a suitable stratified combustion. good.

In the above embodiment, the fuel pressure adjustment according to only the intake air temperature has been described. However, the fuel pressure adjustment may be performed according to both the intake air temperature and the fuel temperature. However, the tendency of the changes in the intake air temperature and the fuel temperature is generally similar, and the effect of the fuel temperature change on the stratified combustion can be reduced by adjusting the fuel pressure based on the intake air temperature.

[0045]

According to the first aspect of the present invention, the fuel pressure can be adjusted in accordance with the intake air temperature at least while the internal combustion engine is operating in the specific operation range. Therefore, for example, by adjusting the fuel spray transport speed by adjusting the fuel pressure so as to offset the change in the fuel spray transport speed due to the change in the intake air temperature, it is possible to obtain the optimum fuel spray transport speed independently of the intake air temperature. it can. Like this
Since the fuel spray transport speed can be constant regardless of the intake air temperature, in a direct injection internal combustion engine whose operation is controlled based on time parameters such as fuel injection start / end timing and ignition timing, regardless of the intake air temperature, A stratified mixture can be reliably formed around the spark plug at the ignition timing, and stable stratified combustion can be obtained. Further, according to the present invention, the time parameter region in which the stratified combustion can be stably performed, that is, the stratified combustion operation region can be substantially widened, and the fuel consumption and the exhaust emission can be improved.

According to the in-cylinder injection internal combustion engine of the second aspect, the fuel pressure can be increased as the intake air temperature rises. By increasing the transport speed, the fuel spray transport speed can be made constant irrespective of the intake air temperature, and stable stratified combustion can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a direct injection engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a fuel system of the engine shown in FIG. 1 together with peripheral elements such as an electronic control unit.

FIG. 3 is a diagram exemplifying a fuel injection control map set based on an engine speed and an average effective pressure;

FIG. 4 is a diagram showing a stable combustion region when the intake air temperature is high and when it is low.

FIG. 5 is a diagram showing a change curve of a fuel spray reaching distance with time when an intake air temperature is high and when it is low.

FIG. 6 is a diagram illustrating a change curve of a fuel spray reaching distance with time when a fuel pressure is high and when the fuel pressure is low.

FIG. 7 is a flowchart of a fuel injection control / fuel pressure adjustment routine executed by the electronic control unit shown in FIGS. 1 and 2;

8 is a diagram illustrating an intake air temperature / fuel pressure map referred to in a fuel injection control / fuel pressure adjustment routine shown in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Spark plug 4 Fuel injection valve 5 Combustion chamber 19 Ignition coil 31 Intake temperature sensor 56 High pressure fuel pump 62 Fuel pressure sensor 64 Electromagnetic proportional pressure control valve 70 Electronic control unit 72 Injection mode selection means 73 Fuel pressure setting means

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/14 310 F02M 61/14 310S

Claims (2)

[Claims] In an in-cylinder injection type internal combustion engine which performs stratified combustion by collecting fuel directly injected from an injection valve into a combustion chamber in a specific operation range in the vicinity of an ignition plug, an intake air temperature detecting means. Fuel pressure adjusting means for adjusting the fuel pressure acting on the injection valve; and controlling the operation of the fuel pressure adjusting means at least at the time of engine operation in the specific operating range based on the intake air temperature detected by the intake air temperature detecting means. A direct injection internal combustion engine, comprising: a control unit. 2. The apparatus according to claim 1, wherein the control means controls the operation of the fuel pressure adjusting means so that the fuel pressure increases as the intake air temperature detected by the intake air temperature detecting means increases. An in-cylinder injection internal combustion engine as described in the above.