JP2004068695A - Fuel control device for direct-injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct-injection engine utilizing an air flow in a cylinder 2 for stratifying a mixture, having improved ignition stability by avoiding trouble in stratifying the mixture resulting from a change in humidity, in particular. <P>SOLUTION: The intake air flowing into the cylinder 2 of the engine 1 has a higher humidity than predetermined is detected in accordance with a signal from a humidity sensor 63 of an air-conditioner (Step S4, S5). In detection, fuel is injected two times by an injector 20 to weaken the degree of the stratification of the mixture in the cylinder 2 (Step S7, S8). At this time, a front stage injection timing is made faster as the humidity of the intake air is higher. The opening of a TSCV 32 is corrected to be wider in a high moisture state for making the flow rate of the intake air smaller (Step S9). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel control device for a direct injection engine that directly injects fuel into a combustion chamber in a cylinder, and particularly to a technical field of air-fuel mixture formation using air flow in a cylinder.
[0002]
[Prior art]
Conventionally, as this type of direct injection engine, there has been known a type of engine that uses an air flow such as swirl or tumble in a cylinder to confine an air-fuel mixture in a cavity or transport the mixture to an electrode side of a spark plug. I have. For example, in the technology disclosed in Japanese Patent Application Laid-Open No. H11-141338, when the engine is in a stratified combustion state, fuel is injected from an injector into a high-pressure combustion chamber at a predetermined timing after the middle stage of the compression stroke of a cylinder, and the fuel is injected into the combustion chamber. While promoting the atomization of fuel spray and mixing with air by collision with the tumble flow, the fuel spray is transported toward the spark plug electrode, and the air-fuel mixture is stratified around the electrode. I have.
[0003]
[Problems to be solved by the invention]
By the way, in the stratified combustion state, at least at the ignition timing of the cylinder, a mixture of a required concentration state must exist near the electrode of the ignition plug, but the fuel is transported by air flow as in the conventional example. In such a configuration, the mixture concentration near the spark plug electrode is constantly changing and is not stable.
[0004]
Therefore, the fuel injection pressure, the injection timing, or the strength of the air flow is usually set so that the concentration of the air-fuel mixture near the electrode substantially peaks before and after the ignition timing, and furthermore, the high concentration state lasts as long as possible. However, in some cases, it is difficult to ensure ignition stability.
[0005]
In this regard, the inventor of the present application has found that the momentum of the air flow changes according to the amount of water vapor contained in the air, which has a great effect on the formation of the air-fuel mixture, and has completed the present invention. Reached. That is, an object of the present invention is to provide a direct injection engine in which stratification of an air-fuel mixture is performed by utilizing air flow in a cylinder, in which stratification of the air-fuel mixture is hindered particularly due to a change in humidity. The present invention aims at improving ignition stability by resolving such problems.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the fuel control device for a direct injection engine according to the present invention, the fuel injection mode is changed so that the degree of stratification of the air-fuel mixture is weakened when the humidity of the air is higher than a predetermined value. The change in the mixture concentration near the ignition plug electrode near the ignition timing of the cylinder is made relatively gentle.
[0007]
Specifically, in the invention of claim 1, a fuel injection valve for directly injecting fuel into a combustion chamber in a cylinder is provided, and when the engine is operated in a stratified combustion state, the fuel injection valve causes the fuel injection valve to at least perform a compression stroke of the cylinder. It is assumed that a fuel control device of a direct injection engine is configured to inject fuel and stratify an air-fuel mixture around an electrode of a spark plug by using air flow in a cylinder. And a humidity state detecting means for detecting that the humidity of the intake air sucked into the cylinder is higher than a predetermined high humidity state. And a fuel injection control means for controlling the fuel injection valve so that the degree of stratification is weakened.
[0008]
With the above configuration, when the engine is operated in a stratified combustion state, the fuel is injected by the fuel injection valve at least in the compression stroke of the cylinder, and the fuel spray moves while being affected by the air flow in the cylinder, and the fine particles of the fuel spray move. Gasification and vaporization and atomization are promoted. The mixture is stratified around the electrodes of the ignition plug before and after the ignition timing of the cylinder.
[0009]
At that time, in a high humidity state where the humidity of the air is particularly high, the momentum of the air flow becomes excessively large due to the presence of a large amount of water vapor in the air, and the timing at which the concentration of the air-fuel mixture near the ignition plug peaks due to this effect. However, at this time, the high-humidity state is detected by the humidity state detecting means, and the fuel injection is controlled by the fuel injection control means so that the degree of stratification of the air-fuel mixture formed around the ignition plug is weakened. The valve is controlled.
[0010]
As a result, the change in the mixture concentration near the spark plug before and after the ignition timing becomes relatively gentle, and even if the peak shifts, for example, if the fuel injection amount is increased, the mixing time becomes longer. A state in which the concentration of air is high can be maintained, thereby improving ignition stability.
[0011]
According to the second aspect of the present invention, the fuel injection control means injects the fuel in a plurality of times by the fuel injection valve when detecting the high humidity state, and collectively injects the fuel when the high humidity state is not detected. And
[0012]
That is, if the fuel is injected in a lump by the fuel injection valve, the degree of stratification of the air-fuel mixture becomes relatively high, so that the concentration of the air-fuel mixture at the peak becomes high even if the fuel injection amount is small. Therefore, fuel efficiency can be reduced while ensuring good ignitability. On the other hand, if the fuel is divided and injected by the fuel injection valve, the early sprayed fuel spray is dispersed relatively large, and it is integrated with the later sprayed fuel spray to form a relative spray. Then, a stratified mixture having a low stratification degree is formed. Therefore, the function and effect of the invention of claim 1 can be sufficiently obtained.
[0013]
According to a third aspect of the present invention, as the fuel injection control means of the second aspect of the present invention, the timing of the earliest injection operation among the plurality of divisions is advanced as the intake air humidity becomes higher. In this case, the momentum of the air flow in the cylinder increases, and as the influence increases, the timing of the earliest injection operation is advanced to form a stratified mixture having a low degree of stratification. As a result, the function and effect of the second aspect of the invention can be further ensured.
[0014]
According to the fourth aspect of the invention, when the high-humidity state is detected by the intake-air-flow-rate adjusting means capable of adjusting the flow velocity of the intake air drawn into the cylinder, and the high-humidity state is detected, the intake flow velocity is lower than when no detection is performed. And the intake flow velocity controlling means for controlling the intake flow velocity adjusting means.
[0015]
Thus, when the high-humidity state is detected by the humidity-state detecting means, the intake-flow-velocity control means is controlled by the intake-flow-velocity control means so that the flow velocity of the intake air is lower than that at the time of non-detection. The momentum of the air flow in the interior will be reduced. In other words, the effects of high humidity can be reduced by lowering the flow velocity, and fluctuations in the air flow can be mitigated, so that ignition stability can be secured without reducing the degree of stratification of the air-fuel mixture so much. In addition, deterioration of fuel efficiency can be minimized.
[0016]
According to the fifth aspect of the present invention, the engine is mounted on the vehicle, and the control system of the air conditioner of the vehicle includes a humidity sensor, and the humidity state detecting unit is configured to detect a humidity based on a signal from the humidity sensor. To detect a high humidity condition. Thus, the high humidity state can be accurately detected based on the signal from the humidity sensor.
[0017]
According to a sixth aspect of the present invention, when the humidity sensor or the control system of the air conditioner fails, at least one of the operation state of the wiper of the vehicle or the information on the humidity of the air obtained from outside is provided when the humidity sensor or the control system of the air conditioner fails. Is configured to detect the high humidity state based on As a result, even when a signal from the humidity sensor cannot be obtained due to a device failure, a high humidity state can be detected.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 shows the overall configuration of a control system for a direct injection engine 1 according to the present invention. In FIG. 1, the engine 1 has a cylinder block 3 in which a plurality of cylinders 2, 2,... (Only one is shown) are provided in series, and a cylinder head 4 arranged on the cylinder block 3. A piston 5 is inserted into each cylinder 2 so as to be able to reciprocate, and a combustion chamber 6 is defined in the cylinder 2 between the crown surface of the piston 5 and the lower surface of the cylinder head 4. The reciprocating motion of the piston 5 is converted into a rotational motion of a crankshaft 8 via a connecting rod 7 and output by the crankshaft 8. The cylinder block 3 has an electromagnetic crank angle sensor 9 at one end of the crankshaft 8 for detecting a rotation angle thereof, and a knock for detecting knocking based on a variation in combustion pressure of each cylinder 2. A sensor 10 and an engine water temperature sensor 11 that faces the inside of a water jacket (not shown) and detects the temperature of the cooling water (engine water temperature) are provided respectively.
[0020]
The cylinder head 4 is provided with two intake ports 12 and two exhaust ports 13 so as to open toward the ceiling surface of the combustion chamber 6 for each of the cylinders 2. Valves 14, 15 are arranged. The intake valve 14 and the exhaust valve 15 are opened by a camshaft (not shown) on the intake side and the exhaust side which are respectively supported inside the cylinder head 4 in synchronization with the rotation of the crankshaft 8. It has become. The camshaft on the intake side is provided with an electromagnetic cam angle sensor 16 for detecting the rotation angle. An ignition plug 17 is provided for each cylinder 2 so as to penetrate the cylinder head 4 in the vertical direction and to be surrounded by the intake and exhaust valves 14 and 15. The electrode at the tip of the spark plug 17 projects downward from the ceiling surface of the combustion chamber 6 by a predetermined distance. The base end of the ignition plug 17 is connected to an ignition circuit 18 (igniter) disposed so as to penetrate the head cover.
[0021]
The crown surface of the piston 5 serving as the bottom of the combustion chamber 6 has a shape on the outer peripheral side that is substantially parallel to the ceiling surface of the combustion chamber 6, while a substantially central portion of the piston 5 crown surface is substantially in plan view. An oval concave portion 5a (see FIG. 4) is provided. Further, an injector (fuel injection valve) 20 is disposed with the injection port facing the peripheral portion of the combustion chamber 6 on the intake side. The injector 20 may be, for example, a known swirl injector that injects fuel as a swirling flow from a nozzle at a tip portion facing the combustion chamber 6 and injects the fuel in a hollow cone shape along the direction in which the axis extends. The present invention is not limited to this, and a slit type or a multi-injection type injector may be used, or a configuration in which the core valve is operated by a piezoelectric element may be used.
[0022]
The base end side of the injector 20 is connected to a fuel distribution pipe 21 common to all the cylinders 2, 2,..., And fuel discharged from the high-pressure fuel pump 22 is injected into each injector 2 by this fuel distribution pipe 21. 20. As will be described in detail later, when fuel is injected by the injector 20 in the compression stroke of the cylinder 2, this fuel spray is transported to the ignition plug 17 side by the flow of intake air in the combustion chamber 6, and A mixture is formed around the electrodes. The fuel distribution pipe 21 is provided with a fuel pressure sensor 23 for measuring the pressure state (fuel injection pressure) of the fuel injected from the injector 20, based on a signal from the fuel pressure sensor 23. The opening of the spill valve of the high-pressure fuel pump 22 is feedback-controlled by an ECU 50 described later. In other words, the high-pressure fuel pump 22 constitutes an injection pressure adjusting unit that can adjust the injection pressure of the fuel by the injector 20.
[0023]
An intake passage 25 is connected to one side surface (right side surface in the figure) of the engine 1 so as to communicate with the intake port 12 of each cylinder 2. The intake passage 25 supplies the intake air filtered by the air cleaner 26 to the combustion chamber 6 of the engine 1, and detects the amount of intake air to the engine 1 in order from the upstream side to the downstream side. A wire type air flow sensor 27, an electric throttle valve 28 for changing the cross-sectional area of the intake passage 25, a throttle sensor 29 for detecting its position, and a surge tank 30 are provided. The throttle valve 28 is not mechanically connected to an accelerator pedal (not shown), and is opened and closed by an electric motor (not shown). The surge tank 30 is provided with a boost sensor 31 for detecting a pressure in the intake passage 25 downstream of the throttle valve 28.
[0024]
The intake passage 25 downstream of the surge tank 30 is an independent passage branching for each cylinder 2, and the downstream end of each independent passage is further branched into two to be individually connected to the intake port 12. It is a branch road communicating with. A throttle valve 32 (Tunble Swirl Control Valve: hereinafter referred to as TSCV) for adjusting the strength of the intake air flow in the combustion chamber 6 is disposed in the branch passage or the independent passage, and is opened and closed by, for example, a stepping motor. Is done. A notch is formed in a part of the valve body of the TSCV 32. In the fully closed state, the intake air flowing downstream only from the notch generates a strong air flow in the combustion chamber 6. On the other hand, as the TSCV 32 is opened, the intake air flows from other than the notch, and the strength of the air flow in the cylinder 2 gradually decreases.
[0025]
An exhaust passage 34 for discharging burned gas (exhaust gas) from the combustion chamber 6 in the cylinder 2 is connected to the other side surface (the left side surface in the figure) of the engine 1. The upstream end of the exhaust passage 34 is constituted by an exhaust manifold 35 connected to the exhaust port 13 of each cylinder 2, and the exhaust passage 34 downstream of the exhaust manifold 35 contains harmful components in the exhaust gas. Two catalytic converters 36 and 37 for purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) are arranged in series.
[0026]
Although not shown in detail, the upstream catalytic converter 36 accommodates a carrier having a honeycomb structure in a casing, and a so-called three-way catalyst catalyst layer is formed on a wall surface of each through hole of the carrier. As is well known in the art, the three-way catalyst 36 is capable of substantially completely purifying HC, CO, and NOx when the air-fuel ratio state of the exhaust gas is in a predetermined state including a substantially stoichiometric air-fuel ratio. The downstream-side catalytic converter 37 accommodates two carriers in series in one casing, forms a so-called NOx storage type catalyst layer on the wall surface of each through hole of the upstream-side carrier, and forms the upstream-side catalytic converter. In addition to constituting the NOx catalyst 38, a catalyst layer of the NOx catalyst is similarly formed on the downstream carrier to constitute the upstream NOx catalyst 39.
[0027]
An oxygen concentration sensor 40 (first oxygen concentration sensor) for detecting the oxygen concentration in the exhaust gas is disposed near the gathering portion of the exhaust manifold 35 of the engine 1, and mainly based on a signal from the sensor 40. Thus, the air-fuel ratio feedback control of the engine 1 is performed. A second oxygen concentration sensor 41 for determining the state of deterioration of the upstream three-way catalyst 36 is provided between the two catalytic converters 36 and 37, and a temperature of exhaust gas flowing into the NOx catalyst 38 is detected. An exhaust gas temperature sensor 42 is provided, and a third oxygen concentration sensor 43 is provided between the two upstream and downstream NOx catalysts 38 and 39.
[0028]
An exhaust passage 34 downstream of the exhaust manifold 35 is an upstream end of an exhaust gas recirculation passage 45 (hereinafter, referred to as an EGR passage) that branches off therefrom and recirculates a part of the exhaust gas to the intake passage 25. Are in communication. The downstream end of the EGR passage 45 is open toward the inside of the surge tank 30, and the EGR passage 45 near the downstream end is provided with an EGR valve 46 composed of a duty solenoid valve. The recirculation amount of exhaust gas in the EGR passage 45 is adjusted by the EGR valve 46. Reference numeral 47 denotes a purge passage that guides blow-by gas leaking from the combustion chamber 6 of each cylinder 2 to the surge tank 30.
[0029]
The above-described ignition circuit 18, injector 20, high-pressure fuel pump 22, throttle valve 28, TSCV 32, and the like are all operated and controlled by an engine control unit 50 (hereinafter, referred to as ECU). On the other hand, as shown in FIG. 2, at least output signals from the crank angle sensor 9, the cam angle sensor 16, the air flow sensor 27, and the like are input to the ECU 50, and furthermore, the operation amount of the accelerator pedal (hereinafter, referred to as the operation amount) , An accelerator opening), and an output signal from a rotational speed sensor 52 for detecting an engine rotational speed (the rotational speed of the crankshaft 8). ing.
[0030]
2, the ECU 50 includes a signal from an external communication antenna 55 corresponding to a road-to-vehicle communication system, a signal from a navigation system 56 mounted on the vehicle, and an air conditioner mounted on the vehicle. A signal from the controller 60 of the apparatus and a signal from the wiper operation switch 65 of the vehicle are input. Here, the controller 60 of the air conditioner detects at least a signal from the indoor temperature sensor 61 for detecting the temperature in the vehicle compartment, a signal from the outdoor temperature sensor 62 for detecting the temperature of the outside air, and the humidity of the outside air. A signal from the humidity sensor 63 and a signal from a target temperature setting switch 64 for setting a target value of the temperature in the vehicle compartment are input, and the operation of an air conditioner (not shown) is controlled in accordance with these.
[0031]
(Overview of engine operation control)
Next, the outline of the operation control of the engine 1 by the ECU 50 will be described. The ECU 50 mainly performs an intake air amount to the engine 1 and a fuel injection amount for each cylinder 2 based on signals from the above-described sensors. It controls the injection timing and the ignition timing, and further controls the strength of the intake air flow in the cylinder 2 and the recirculation ratio of the exhaust gas. For example, as shown in an example of a control map in FIG. 3, a stratified combustion region (S) is set in advance on the low speed and low load side in the entire warm operation region of the engine 1. A stratified charge combustion mode is set in which fuel is injected mainly in the compression stroke of the cylinder 2 to burn the air-fuel mixture unevenly distributed around the electrode of the ignition plug 17. At this time, the throttle valve 28 is relatively wide open to reduce pump loss, and as a result, the average air-fuel ratio in the combustion chamber 6 of each cylinder 2 is significantly leaner than the stoichiometric air-fuel ratio ( For example, A / F> 30).
[0032]
On the other hand, the region other than the stratified combustion region (S) is a so-called uniform combustion region (H). Here, fuel is injected by the injector 20 mainly in the intake stroke of the cylinder 2, and the intake air and the fuel are separated in the combustion chamber 6. A uniform combustion mode is achieved in which the mixture is sufficiently mixed to form a substantially uniform mixture in the entire combustion chamber 6 and then burn. In most of the uniform combustion region (H), the air-fuel ratio of the air-fuel mixture becomes substantially equal to the stoichiometric air-fuel ratio (A / F７14.7) based on the fuel injection amount, the opening of the throttle valve 28, and the like. Especially, in the vicinity of full load, control is performed so as to be richer than the stoichiometric air-fuel ratio (for example, A / F = 12 to 14) so that a large output corresponding to a high load can be obtained. I have.
[0033]
The feature of the present invention lies mainly in the formation of an air-fuel mixture in the stratified combustion region (S). More specifically, in the engine 1 of this embodiment, as shown in FIG. 4, when viewed from a direction orthogonal to the cylinder center line Z, the injector 20 is moved slightly downward from the intake side peripheral portion of the combustion chamber 6 (the piston 5 crown surface). In order to inject fuel (in the direction), it is arranged inclined with respect to the cross section of the cylinder 2. As shown in the figure, the tilt angle of the injector 20 is substantially positive in the lower part of the conical fuel spray with respect to the tumble flow T flowing along the concave portion 5a of the piston 5 crown at the fuel injection timing. Are set to collide with each other.
[0034]
When fuel is injected from the injector 20, a part of the fuel spray rides on the tumble flow T flowing along the ceiling of the combustion chamber 6 and moves to the spark plug 17 side, as described above. The lower portion of the fuel spray, which has lost the moving speed downward due to collision with the tumble flow T, is directed upward (toward the ceiling of the combustion chamber 6) by the tumble flow T without adhering to the crown surface of the piston 5. Is done. In other words, the fuel spray is transported as a whole on the tumble flow T toward the electrode of the spark plug 17, during which vaporization and atomization is promoted, and around the ignition timing of the cylinder 2, around the electrode of the spark plug 17. A mixed air mass distributed in layers is formed. In other words, the engine 1 of this embodiment controls the behavior of the fuel spray injected by the injector 20 after the middle stage of the compression stroke of the cylinder 2 using the tumble flow T in the combustion chamber 6 in the stratified combustion state. The mixture is stratified around the electrodes of the ignition plug 17 by the ignition timing.
[0035]
By the way, when the fuel spray is transported by the air flow in the cylinder 2 as described above, if the intensity of the tumble flow T becomes lower than the expected value for some reason, the mixture is ignited by the ignition timing. There is a possibility that the plug does not reach around the plug 17. Further, the air-fuel mixture once stratified around the ignition plug 17 is further flown or diffused by the tumble flow T, so that the concentration of the air-fuel mixture near the electrode of the ignition plug 17 always changes. . For example, FIG. 5 shows a local change in the air-fuel ratio at a predetermined position near the electrode of the spark plug 17, and as shown by a solid line in FIG. Although the gas enters the flammable range, it returns to a state leaner than the flammable range after a relatively short time after passing through a rich peak.
[0036]
In this regard, the injection pressure and the injection timing of the fuel by the injector 20 are usually set so that the local air-fuel ratio near the electrode of the ignition plug 17 substantially peaks near the ignition timing and the rich state is maintained as long as possible. Alternatively, the intensity of the air flow is controlled, but even in such a case, the period in which the local air-fuel ratio around the ignition plug 17 is in the flammable range is not so long as shown in the figure. If the ignition timing deviates, the ignition stability may be impaired.
[0037]
The inventor of the present application has conducted intensive studies on the formation process of the layered air-fuel mixture around the ignition plug 17 and the change in the local air-fuel ratio associated with the process, and as a result, the air flow was determined by the amount of water vapor contained in the air. Momentum greatly changed, and this was found to have a great effect on the mixture formation around the spark plug 17. That is, in the case of the engine 1 of this embodiment, for example, when the humidity of the air is high, the momentum of the tumble flow T generated in the cylinder 2 increases, and as a result, the time when the air-fuel mixture reaches around the spark plug 17 is reduced. As the air-fuel ratio becomes earlier, the subsequent movement and diffusion of the air-fuel mixture also become faster, and the local air-fuel ratio around the spark plug 17 becomes lean before the ignition timing, which greatly reduces the ignition stability. Become.
[0038]
On the other hand, in this embodiment, when the engine 1 is in the stratified combustion mode, the humidity of the intake air drawn into each cylinder 2 of the engine 1 is estimated, and when the humidity is higher than a predetermined value (in a high humidity state). ) By intentionally reducing the degree of stratification of the air-fuel mixture, the local air-fuel ratio around the spark plug 17 near the ignition timing, that is, the change in the air-fuel mixture concentration is made relatively gentle, and the ignition plug 17 The period in which the surrounding local air-fuel ratio is in the flammable range is extended.
[0039]
Hereinafter, a specific control procedure of the engine 1 by the ECU 50 will be described with reference to a flowchart shown in FIG. 6. First, in step S1 after the start, the crank angle sensor 9, the cam angle sensor 16, the air flow sensor 27, the accelerator Output signals from the opening degree sensor 51, the rotation speed sensor 52, and the like are input, and the data temporarily stored in the RAM of the ECU 50 is read. Subsequently, in step S2, the engine rotation speed is calculated based on the signal from the rotation speed sensor 52, and the target load is calculated based on the calculated engine rotation speed and the signal from the accelerator opening sensor 51. As a method of calculating the target load, for example, an optimal value corresponding to the engine rotation speed and the accelerator opening is experimentally obtained in advance and set as a map, and this map is electronically stored in the RAM of the ECU 50. Then, the values corresponding to the current engine rotation speed and accelerator opening may be read from the map.
[0040]
Subsequently, in step S3, the current operation mode of the engine 1 is determined from the control map as shown in FIG. 3 based on the target load and the engine speed of the engine 1 obtained as described above. That is, if the engine 1 is in the illustrated uniform combustion region (H), the determination in the uniform combustion mode is NO, and the process proceeds to step S10 described later, while if the engine 1 is in the stratified combustion region (S), the determination is in the stratified combustion mode. Is YES, the process proceeds to step S4, and information on the humidity of the intake air is acquired. Specifically, a signal from the humidity sensor 63 is input to the ECU 50 via the controller 60 of the air conditioner and the in-vehicle LAN.
[0041]
If the humidity sensor 63 or the controller 60 is out of order or the communication system has a defect or the like and the signal from the humidity sensor 63 cannot be input as described above, the wiper operation is performed at that time. Depending on the state of the switch 65 (on / off state) and information on humidity from outside the vehicle (eg, pinpoint climate information corresponding to the current position of the vehicle detected by the navigation system 56, regional climate information obtained by road-to-vehicle communication, etc.), Estimate the humidity of the intake air. Then, in step S5, it is determined whether the intake air humidity detected or estimated as described above is equal to or higher than a predetermined value. If the determination is NO and the intake air humidity is lower than the predetermined value, the process proceeds to step S6. Fuel is collectively injected by the injector 20 in the compression stroke of each cylinder 2 so that the engine 1 is in a stratified combustion state as usual (see FIG. 7A).
[0042]
On the other hand, if the determination in step S5 is YES and the intake air humidity is equal to or higher than a predetermined value, that is, if it is detected that the intake air humidity is higher than or equal to a predetermined high humidity, the process proceeds to step S7, and each cylinder 2 Each time the fuel injection amount by the injector 20 is increased and corrected, and the fuel injection is divided into two parts, the preceding (earliest of the plurality) injection timing and the subsequent injection timing are set. . At this time, as schematically shown in FIG. 7 (b), the injection timing of the latter stage is substantially the same as the case of the above-described batch injection (FIG. (A)) when the injection port of the injector 20 is closed in the injection operation. On the other hand, the injection timing of the former stage is set in the range from the middle stage of the intake stroke to the first half of the compression stroke as shown by an arrow in FIG. Is set such that the higher the humidity of the intake air, the closer to the advanced side.
[0043]
When the fuel is injected in two divided portions in this manner, the fuel spray generated by the injection operation at the front stage of the injector 20 is relatively large and dispersed in the cylinder 2, and the fuel spray generated by the injection operation at the subsequent stage catches up with the fuel injection. As a result, a stratified mixture having a lower stratification degree, that is, a gradual change in the spatial distribution of the air-fuel ratio, is formed. As a result, the change in the local air-fuel ratio around the ignition plug 17 becomes relatively gentle, as shown by the one-dot chain line in FIG. 5, and the change in the local air-fuel ratio remains in the flammable range for a relatively long period as compared with the case of the batch injection. , The ignition stability is significantly improved.
[0044]
Then, when the injection timing of the former stage and the latter stage set as described above is reached, the injector 20 is opened for each cylinder 2 to inject fuel (step S8). Subsequently, in step S9, an opening correction value for correcting the target opening is set so that the TSCV 32 opens more as the humidity of the intake air increases, and the opening correction value is stored in the RAM of the ECU 50, and thereafter, To return. That is, although the detailed description is omitted, the control program of the TSCV 32 is executed by the CPU of the ECU 50 in parallel with the control program shown in the flow of FIG. 6. When the target opening of the TSCV 352 is determined in this control, The opening correction value is read from the RAM and used.
[0045]
On the other hand, in step S10, in which it is determined that the engine 1 is in the uniform combustion mode in step S3, as shown in FIG. 7 (c), fuel is injected by the injector 20 during the intake stroke for each cylinder 2 of the engine 1, as shown in FIG. The engine 1 is made to be in a uniform combustion state, and then returns.
[0046]
The engine control procedure shown in the flowchart of FIG. 6 is realized by executing a program electronically stored in the memory of the ECU 50 by the CPU. The invention is provided with software requirements. That is, steps S4 and S5 of the flow constitute a humidity state detecting means 50a for detecting that the humidity of the intake air taken into the cylinder 2 of the engine 1 is higher than a predetermined high humidity state. The state detecting means 50a basically detects a high humidity state based on a signal from the humidity sensor 63 of the air conditioner of the vehicle, and when the control system of the humidity sensor 63 or the air conditioner breaks down, the wiper of the vehicle is used. It is configured to detect a high-humidity state based on the operation state of the device and information on the humidity of the air obtained from outside.
Further, the fuel injection control means 50b which controls the operation of the injector 20 so that the stratified degree of the air-fuel mixture becomes weaker at the time of detection of the high humidity state than at the time of non-detection by the steps S7 and S8 of the flow. Have been. The fuel injection control means 50b is configured such that when the high humidity state is detected, the injector 20 injects the fuel into two equal parts and injects the fuel, and the higher the intake air humidity, the more advanced the earlier injection timing. I have.
[0047]
Further, in step S9, the intake flow rate control means 50c is configured to correct the opening degree of the TSCV 32 so that the flow rate of intake air is lower when a high humidity state is detected than when it is not detected.
[0048]
Therefore, according to the fuel control device A for the direct injection engine according to this embodiment, when the engine 1 is operated in the stratified combustion mode in the stratified combustion region (S) on the low-speed low-load side, at least the cylinder 2 is operated by the injector 20. During the compression stroke, fuel is injected, and while this fuel spray is being transported by the tumble flow T in the cylinder 2, atomization and vaporization and atomization thereof are promoted, and around the ignition plug 17 near the ignition timing of the cylinder 2. The mixture is stratified.
[0049]
At this time, if the humidity of the air is in a normal range where the air humidity is not particularly high (may be set in advance), the fuel is collectively injected by the injectors 20 of the respective cylinders 2. Since the stratification degree becomes relatively high, the concentration of the air-fuel mixture at the peak can be sufficiently increased even if the fuel injection amount is small, and the fuel efficiency is reduced while ensuring good ignitability.
[0050]
On the other hand, when the humidity of the air is particularly high (high-humidity state), the momentum of the tumble flow T increases due to the water vapor in the air, and as a result, the timing at which the local air-fuel ratio around the spark plug 17 reaches a peak varies greatly. However, at this time, the fuel is divided into two injections by the injector 20, and the stratification degree of the air-fuel mixture is weakened, the local air-fuel ratio fluctuates moderately, and the fuel is increased. For a relatively long period of time, the rich state of the air-fuel ratio can be maintained, and high ignition stability can be secured. In addition, the higher the humidity of the intake air, the more advanced the injection timing in the preceding stage is, so that the degree of stratification of the air-fuel mixture is weakened, so that the above-mentioned effects can be obtained more reliably.
[0051]
In addition, in the high-humidity state, the opening degree of the TSCV 32 is increased as the humidity of the intake air is increased, so that the intake flow velocity is reduced. As a result, the momentum of the tumble flow T in the cylinder 2 is reduced. The effect of high humidity can be reduced. Therefore, as described above, in a high humidity state, the stratification degree of the air-fuel mixture is weakened to mitigate the fluctuation of the local air-fuel ratio. At this time, a sufficient effect can be obtained even if the stratification degree of the air-fuel mixture is not so weakened. As a result, the fuel increase can be minimized, so that the deterioration of fuel efficiency can be minimized.
[0052]
It should be noted that the configuration of the present invention is not limited to the configuration of this embodiment, but also includes other various configurations. For example, in this embodiment, the fuel is divided into two and injected by the injector 20 in the high humidity state. However, the invention is not limited thereto, and the fuel may be divided and injected three or more times. It may be. Further, the air flow in the cylinder 2 used for stratifying the fuel spray is not limited to the tumble flow as in this embodiment, but may be a swirl flow.
[0053]
Further, in step S9 of the flow of FIG. 6 of this embodiment, instead of correcting the opening degree of the TSCV 32, the fuel pressure may be corrected so that the fuel injection pressure by the injector 20 decreases in a high humidity state. Good. In this way, even when the momentum of the tumble flow T increases in a high humidity state, the fuel pressure decreases by controlling the high-pressure supply pump 22 and the momentum of the fuel spray decreases, thereby correcting the opening of the TSCV 32. The same operation and effect as described above can be obtained. Further, in this case, the injection pressure control means for controlling the high-pressure supply pump 22 so that the fuel pressure becomes higher when the high humidity state is detected than when the high humidity state is not detected in the step S9.
[0054]
【The invention's effect】
As described above, according to the control apparatus for a direct injection engine according to the first aspect of the present invention, in the case where the air-fuel mixture is stratified by utilizing the air flow in the cylinder, the humidity of the air is higher than a predetermined value. When the air-fuel ratio is high, the fuel injection valve is controlled so that the degree of stratification of the air-fuel mixture is weakened, and the change in the air-fuel mixture concentration near the electrode of the ignition plug is made relatively gentle, so that the air-fuel mixture is maintained for a relatively long period of time. Can be maintained at a high concentration, thereby improving ignition stability.
[0055]
According to the second aspect of the present invention, the fuel is normally injected in a lump, so that the degree of stratification of the air-fuel mixture is relatively high, and fuel efficiency can be reduced while ensuring good ignitability. On the other hand, in the high humidity state, by dividing and injecting the fuel, a stratified mixture having a relatively low stratification degree can be formed, whereby the effect of the first aspect of the invention can be sufficiently obtained.
[0056]
According to the third aspect of the invention, as the intake air humidity becomes higher, the timing of the earliest injection operation is advanced to lower the degree of stratification of the air-fuel mixture, so that the effect of the second aspect of the invention is more reliable. It will be.
[0057]
According to the fourth aspect of the present invention, when the high humidity state is detected, the increase in the momentum of the air flow due to the high humidity is reduced by controlling the intake flow rate adjusting means so that the flow rate of the intake air becomes lower than that at the time of non-detection. can do. Therefore, the ignition stability can be ensured without reducing the degree of stratification of the air-fuel mixture so much, and the deterioration of fuel efficiency can be minimized.
[0058]
According to the invention of claim 5, it is possible to accurately detect the high humidity state based on the signal from the humidity sensor included in the control system of the air conditioner of the vehicle.
[0059]
According to the invention of claim 6, even when the signal from the humidity sensor cannot be obtained due to the failure of the device, the detection of the high humidity state is performed based on the operation state of the wiper and the information on the humidity of the air obtained from outside. It becomes possible.
[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 block diagram of a control system of the engine.
FIG. 3 is a diagram illustrating an example of a control map in which an operation region in which an engine is in a stratified combustion state or a uniform combustion state is set.
FIG. 4 is an explanatory diagram showing a process of forming a stratified mixture by a tumble flow.
FIG. 5 is a graph showing a change in a local air-fuel ratio around an ignition plug.
FIG. 6 is a flowchart showing an outline of engine control.
FIG. 7 is an explanatory diagram schematically showing injection timings of a first stage and a second stage.
[Explanation of symbols]
Ａ Fuel control system for direct injection engine
T Tumble flow (air flow in cylinder)
1 engine
2 cylinders
6 Combustion chamber
17 Spark plug
20 Injector (fuel injection valve)
32 TSCV (intake flow rate adjustment means)
50 ECU (Engine Control Unit)
50a humidity state detecting means
50b fuel injection control means
50c intake flow rate control means
60 Air Conditioner Controller (Air Conditioner Control System)
63 Humidity sensor

Claims (6)

A fuel injection valve for directly injecting fuel into a combustion chamber in a cylinder is provided, and when the engine is operated in a stratified combustion state, the fuel is injected by the fuel injection valve at least in a compression stroke of the cylinder. In a fuel control device for a direct injection engine, the air-fuel mixture is stratified around an electrode of a spark plug using
Humidity state detecting means for detecting that the humidity of the intake air sucked into the cylinder is higher than a predetermined high humidity state,
A fuel injection control means for controlling the fuel injection valve such that the degree of stratification of the air-fuel mixture becomes weaker when the high humidity state is detected by the humidity state detection means than when the high humidity state is not detected. Fuel control device for injection engine. In claim 1,
The fuel injection control means is configured to inject fuel in a plurality of times by the fuel injection valve when detecting the high humidity state, and to collectively inject the fuel when the high humidity state is not detected. A fuel control device for a direct injection engine. In claim 2,
The fuel injection control device for a direct injection engine, wherein the fuel injection control means is configured to advance the timing of the earliest injection operation among the plurality of injections as the intake air humidity increases. In claim 1,
Intake air flow rate adjusting means capable of adjusting the flow rate of intake air taken into the cylinder;
When detecting a high humidity state by the humidity state detecting means, the direct injection engine comprises: Fuel control device. In claim 1,
The engine is mounted on the vehicle,
The control system of the air conditioner of the vehicle includes a humidity sensor,
The fuel control device for a direct injection engine, wherein the humidity state detecting means is configured to detect a high humidity state based on a signal from the humidity sensor. In claim 5,
The humidity state detecting means is configured to detect a high humidity state based on at least one of an operation state of a wiper of the vehicle and information on humidity of air obtained from outside when a humidity sensor or a control system of the air conditioner fails. A fuel control device for a direct injection engine.

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