JP2003003885A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

(57) [PROBLEMS] To provide a fuel injection control for an internal combustion engine capable of ensuring a good combustion state and a substantially proper air-fuel ratio when the engine temperature is low, thereby improving exhaust gas characteristics. Provide equipment. SOLUTION: A fuel injection control device 1 for an internal combustion engine 3 has an E
CU2 is provided. When the detected engine coolant temperature TW is equal to or lower than the predetermined lower limit coolant temperature # TWISO0, the ECU 2 determines the fuel injection end timing THETAINJ as the intake valve 4
From the intermediate crank angle CA2 position between the start point and the end point of the buffer curve portion CINS of the valve lift curve CIN, the distance DA between the end point and the intermediate crank angle CA2 position, the crank angle CA4 position beyond the end point Is set to a predetermined low water temperature injection end timing #THETAjk within the crank angle range (CA2 to CA4) up to.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for controlling fuel injection of an internal combustion engine which injects fuel into an intake port of a cylinder.

[0002]

2. Description of the Related Art Conventionally, as this type of fuel injection control device, for example, the one described in Japanese Patent Publication No. 4-13533 is known. In this fuel injection control device, the cooling water temperature of the internal combustion engine is detected by the water temperature sensor, and when the detected water temperature is less than the predetermined value, that is, when the internal combustion engine is not sufficiently warm, the fuel injection into the intake port of the cylinder, It is performed at a predetermined time other than the intake stroke. As a result, the residence time of the fuel in the cylinder is increased and the vaporization of the fuel is promoted. Further, when the detected water temperature is equal to or higher than a predetermined value, that is, when the internal combustion engine is sufficiently warmed, fuel injection is performed at a predetermined timing in the latter half of the intake stroke.

[0003]

According to this conventional fuel injection control device, exhaust gas characteristics are deteriorated for the following reasons. That is, in general, when the internal combustion engine is not sufficiently warm and its cooling water temperature is low, if fuel injection into the intake port is executed at a time other than the intake stroke, the fuel is difficult to evaporate due to the low temperature. Since there is almost no intake air flow in the intake pipe, the degree of atomization of the fuel is low, and the fuel easily adheres to the wall surface of the intake port. Therefore, the adhered fuel flows into the combustion chamber during the intake stroke, so that the amount of unburned gas generated increases and the HC concentration in the exhaust gas rises. As a result, the exhaust gas characteristics deteriorate.

Further, as described above, when the cooling water temperature is low, the atomization state of the fuel is not good, so during sudden acceleration, etc., the air-fuel ratio tends to fluctuate to the lean side. The amount needs to be increased and corrected quickly and appropriately according to the change in the intake air amount. On the other hand, in the above-mentioned conventional fuel injection control device, when the water temperature is low, the fuel injection is executed at a timing other than the intake stroke in which the intake air flow is almost nonexistent. Even if the fuel amount is set according to the change in the intake air amount, the fuel amount thus set cannot be properly supplied into the combustion chamber, and the air-fuel ratio tends to change toward the lean side.

The present invention has been made in order to solve the above problems, and can secure a good combustion state and a substantially proper air-fuel ratio when the engine temperature is low.
An object of the present invention is to provide a fuel injection control device for an internal combustion engine that can improve exhaust gas characteristics.

[0006]

In order to achieve this object, the invention according to claim 1 proposes a buffer curve portion C at the initial stage of valve opening.
The intake valve 4 is opened and closed by a cam having a cam profile that produces a valve lift curve CIN having INS (for example, the intake cam 6a in the embodiment (hereinafter the same in this section)) and fuel is injected into the intake port of the cylinder. In the fuel injection control device 1 for the internal combustion engine 3, the engine temperature detecting means (water temperature sensor 23) for detecting the engine temperature (engine water temperature TW) of the internal combustion engine 3 and the detected engine temperature (engine water temperature TW) are predetermined. Temperature (predetermined lower limit water temperature #
TWIS0) or less, the fuel injection end timing THETAINJ is set from the intermediate crank angle position (crank angle CA2 position) between the start point (crank angle CA1) and the end point (crank angle CA3) of the buffer curve portion CINS.
The interval DA between the end point (crank angle CA3) and the intermediate crank angle position (crank angle CA2 position) DA, the crank angle position beyond the end point (crank angle CA3) (crank angle C3)
Injection end timing setting means (ECU2, steps 3, 4) for setting the first timing (injection end timing #THETAjk for a predetermined low water temperature) within the crank angle range (CA2 to CA4) up to the A4 position); It is characterized by including.

According to this fuel injection control device for the internal combustion engine, when the detected engine temperature is equal to or lower than the predetermined temperature, the end timing of the fuel injection is an intermediate crank angle position between the start point and the end point of the buffer curve portion. From the end point to the intermediate crank angle position, the first timing is set within the crank angle range from the end point to the crank angle position. As described above, when the engine temperature is low, the end timing of fuel injection is set so as to start opening the intake valve, that is, the early stage of the intake stroke, so that it is different from the conventional case where fuel injection is performed at times other than the intake stroke. Differently, by performing the fuel injection in the state where the intake air flow exists in the intake pipe, the atomization of the fuel can be promoted and the amount of the fuel adhering to the wall surface of the intake port can be further reduced. In general, when the engine temperature is low and fuel injection is performed when the valve lift of the intake valve is large, that is, when the flow rate of the intake air is high, the fuel is rapidly conveyed to the combustion chamber without being atomized. If the burrs adhere to the wall surface, the HC concentration in the exhaust gas may increase. On the other hand, in the present invention, the fuel injection is performed at the timing of the early stage of the intake stroke in which the flow velocity of the intake air is relatively small, so that atomization of the fuel can be promoted to some extent and then supplied to the combustion chamber. From the above, it is possible to burn the fuel in a better combustion state, and by reducing the HC concentration in the exhaust gas,
Exhaust gas characteristics can be improved. Further, as described above, since the fuel injection is executed in the state where the intake air flow exists, unlike the conventional case, the fuel amount set according to the actual change of the intake air amount is appropriately burned at the time of sudden acceleration. The air-fuel ratio can be supplied to the chamber, thereby suppressing the fluctuation of the air-fuel ratio toward the lean side and ensuring a substantially proper air-fuel ratio.

According to a second aspect of the present invention, in the fuel injection control device 1 for the internal combustion engine 3 according to the first aspect, the injection end timing setting means (ECU 2, Steps 3, 5) is the engine temperature (engine water temperature TW). Is higher than a predetermined temperature (predetermined lower limit water temperature # TWIS0), the fuel injection end timing THETAINJ is set to the crank angle position (crank angle CA6) where the valve lift amount of the intake valve 4 becomes the maximum value.
Position, including a predetermined crank angle range (CA5)
~ CA7) is set to a second timing (injection end timing #THETAJJK for a predetermined high water temperature).

According to this fuel injection control device for the internal combustion engine, when the engine temperature is higher than the predetermined temperature, the fuel injection end timing is in the vicinity of the crank angle position where the valve lift amount of the intake valve becomes maximum. Is set to the second timing within the predetermined crank angle range. in this way,
When the internal combustion engine is warm and the fuel is liable to vaporize, the fuel injection is performed when the mass velocity of the intake air is at or close to the maximum, so the fuel adheres to the wall of the intake port as much as possible. It is possible to generate a more homogeneous mixture while avoiding it. As a result, a good combustion state can be ensured and exhaust gas characteristics can be improved.

According to a third aspect of the present invention, in the fuel injection control device 1 for the internal combustion engine 3 according to the second aspect, the injection end timing setting means sets the engine temperature (engine water temperature TW) to a predetermined temperature (predetermined lower limit water temperature). (# TWIS0) when changing across, the fuel injection end timing THETAI
NJ is set to the first and second timings (injection end timing #THETA for predetermined low water temperature and high water temperature).
jk, #THETAJJK) from one side to the other, the timing changing means (ECU 2, steps 7 to 13) is provided.

According to this fuel injection control apparatus for an internal combustion engine, when the engine temperature changes across a predetermined temperature, the timing change setting means shifts the fuel injection end timing from the first timing to the second timing. hand,
Or, it is gradually changed toward the opposite. Therefore, the transition of the fuel injection end timing can be smoothly performed without causing a sudden change in the air-fuel ratio. Thereby, good drivability can be secured and stable exhaust gas characteristics can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A fuel injection control apparatus for an internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a fuel injection control device of the present embodiment and an internal combustion engine to which the fuel injection control device is applied. As shown in the figure, this fuel injection control device 1 is
It is equipped with CU2. As will be described later, the ECU 2 executes fuel injection control and the like according to the operating state of an internal combustion engine (hereinafter referred to as “engine”) 3.

The engine 3 is a four-cylinder DOHC gasoline engine having an intake camshaft 6 and an exhaust camshaft 7, and is provided with a pair of intake valves 4 and exhaust valves 5 for each cylinder (only one of which is shown in the figure). ). The intake and exhaust camshafts 6 and 7 are connected to the crankshaft 9 via a timing belt (not shown), and rotate once every two rotations of the crankshaft 9.

The intake camshaft 6 is provided with four intake cams 6a (only one is shown) for opening and closing the four intake valves 4, respectively. Each intake cam 6a (cam)
As the intake camshaft 6 rotates, the intake valve 4 shown in FIG.
And a cam profile that produces a valve lift curve CIN of Regarding this valve lift curve CIN,
It will be described later.

Further, the exhaust cam shaft 7 is provided with four exhaust cams 7a (only one is shown) for opening and closing the four exhaust valves 5, respectively. Each exhaust cam 7a has a cam profile that produces a valve lift curve CEX of the exhaust valve 5 shown in FIG. 2 as the exhaust cam shaft 7 rotates.

Further, a cam phase varying mechanism (VTC) 8 is provided at one end of the intake camshaft 6.
The cam phase varying mechanism 8 operates by being supplied with hydraulic pressure, and the intake cam 6a for the crankshaft 9 is operated.
The phase (hereinafter, simply referred to as “cam phase”) CAIN is advanced or retarded steplessly to accelerate or delay the opening and closing timings of the intake valve 4.

An electromagnetic control valve 10 is connected to the cam phase changing mechanism 8. This electromagnetic control valve 10 is an EC
It is driven by the drive signal from U2, and the hydraulic pressure from the hydraulic pump (not shown) of the lubrication system of the engine 3 is supplied to the cam phase variable mechanism 8 according to the duty ratio DOUT of the drive signal. As a result, the cam phase variable mechanism 8 advances or retards the cam phase CAIN between the most retarded position and the most advanced position. The angle between the most retarded position and the most advanced position is a predetermined value (for example, cam angle 30 ° = crank angle 60).
゜) is set.

Next, the valve lift curve CIN of the intake valve 4 will be described with reference to FIGS. 2 and 3. In FIG. 2, the valve lift curve CIN shown by the solid line is held by the cam phase varying mechanism 8 at a predetermined cam phase CAIN0 (see FIG. 8) between the most retarded position and the most advanced position. The valve lift curve CIN indicated by the broken line is when the cam phase CAIN is held on the retard side with respect to the predetermined cam phase CAIN0. Further, FIG. 3 shows the TD at the beginning of the intake stroke in the valve lift curve of the intake valve 4 and the exhaust valve 5 shown in FIG.
This is an enlarged view of the portion near the C position. In the present embodiment, the TDC position at the beginning of the intake stroke is used as the origin, and the crank angle position on the front side of this is represented by a negative value and the crank angle position on the rear side thereof is represented by a positive value. Further, hereinafter, the TDC position at the beginning of the intake stroke is simply referred to as the TDC position.

As shown in both figures, the initial portion of the valve lift curve CIN of the intake valve 4 when the valve is opened is the buffer curve portion CINS. The buffer curve portion CINS has a shape that rises more gently than the subsequent portions, and the width in the horizontal axis direction, that is, the interval from the start point to the end point is a predetermined value 2 · DA (for example, a crank angle of 38 °). Minutes). Further, when the cam phase CAIN is held at the predetermined cam phase CAIN0, the buffer curve portion CI
The starting point of NS is a crank angle CA1 position (for example, a crank angle of -38 ° position, that is, a crank angle of 3 degrees from the TDC position).
8 °, front position), end point is crank angle C
It is located at the A3 position (for example, the TDC position). Further, the valve lift amount of the intake valve 4 is set to have a maximum value at the crank angle CA6 position (for example, the crank angle 105 ° position).

Further, when the cam phase CAIN is changed to the retard side from the predetermined cam phase CAIN0 by the cam phase varying mechanism 8, accordingly, as shown by the broken line in FIG.
The valve lift curve of the intake valve 4 is changed so as to shift to the retard side. On the other hand, although not shown, when the cam phase CAIN is changed to the advanced side with respect to the predetermined cam phase CAIN0, the valve lift curve of the intake valve 4 is also changed to the advanced side accordingly.

Further, a cam angle sensor 20 is provided at the end of the intake camshaft 6 opposite to the cam phase varying mechanism 8. The cam angle sensor 20 is composed of, for example, a magnet rotor and an MRE pickup,
As the intake camshaft 6 rotates, the pulse signal C
The ECU 2 outputs an AM signal for each predetermined cam angle (for example, 1 °).
Output to.

On the other hand, in the vicinity of the throttle valve 12 of the intake pipe 11 of the engine 3, a throttle valve opening sensor 21 composed of, for example, a potentiometer is provided. The throttle valve opening sensor 21 detects the opening of the throttle valve 12 (hereinafter referred to as “throttle valve opening”) θTH.
Is detected and the detection signal is sent to the ECU.

Further, an intake pipe absolute pressure sensor 22 is provided downstream of the throttle valve 12 of the intake pipe 11. The intake pipe absolute pressure sensor 22 is composed of, for example, a semiconductor pressure sensor, detects the intake pipe absolute pressure PBA in the intake pipe 11, and outputs the detection signal to the ECU 2.

The intake pipe 11 is connected to each of the four cylinders via the four branch portions 11b of the intake manifold 11a. In each branch portion 11b, an injector 13 is provided on the upstream side of an intake port (not shown) of each cylinder.
Is attached. Each injector 13 is driven by a drive signal from the ECU 2 when the engine 3 is operating, and injects fuel to the upstream side of the intake port in the corresponding branch portion 11b.

Further, a water temperature sensor 23 composed of, for example, a thermistor is attached to the main body of the engine 3. The water temperature sensor 23 (engine temperature detection means) detects an engine water temperature TW (engine temperature) that is the temperature of the cooling water circulating in the cylinder block of the engine 3, and outputs the detection signal to the ECU 2.

A crank angle sensor 24 is provided on the crankshaft 9 of the engine 3. The crank angle sensor 24 has a CRK signal and a TDC signal, both of which are pulse signals as the crankshaft 9 rotates.
The signal is output to the ECU 2.

As the CRK signal, one pulse is output every predetermined crank angle (for example, 30 °). The ECU 2 calculates the rotational speed NE of the engine 3 (hereinafter referred to as “engine rotational speed”) NE in accordance with the CRK signal, and at the same time, CRK
The cam phase CAIN is calculated according to the signal and the CAM signal from the cam angle sensor 20 described above. The TDC signal is a signal indicating that the piston 14 of each cylinder is located at a predetermined crank angle position slightly before the TDC position, and one pulse is output for each predetermined crank angle.

ECU 2 (injection end timing setting means,
The timing change setting means) is composed of a microcomputer including an I / O interface, a CPU, a RAM and a ROM. The ECU 2 determines the operating state of the engine 3 in accordance with the input signals from the various sensors 20 to 24 described above, and determines the injector 13 of the injector 13 in accordance with the control program stored in the ROM in advance and the data stored in the RAM. Fuel injection time TOUT
And the fuel injection end timing THETAINJ is calculated for each cylinder. The calculation process of the fuel injection end timing (hereinafter referred to as “injection end timing”) THETAINJ will be described later. Further, the fuel injection time TOUT and the injection end timing THETA
The injection start timing is calculated for each cylinder based on INJ, and at the injection start timing thus calculated, a drive signal based on the fuel injection time TOUT is output to the injector 13 for the cylinder, so that the fuel injection is performed for the cylinder. Control for each.

Further, the ECU 2 calculates the target cam phase CAINCMD according to the operating state of the engine 3, and determines the duty ratio DOUT of the electromagnetic control valve 10 based on the target cam phase CAINCMD and the cam phase CAIN. By outputting a drive signal based on this duty ratio DOUT to the electromagnetic control valve 10, the cam phase control is executed so that the cam phase CAIN becomes the target cam phase CAINCMD.

Hereinafter, the injection end timing THETAIN
The calculation process of J will be described with reference to the flowcharts of FIGS. 4 and 5. This processing is executed in synchronization with each input of the TDC signal. At this time, the injection end timing T for one cylinder is determined by one routine.
Since HETAINJ is calculated, the injection end timing THETAINJ for all four cylinders is
It is calculated by executing it once.

As shown in FIG. 4, in this process, first, in step 1 (abbreviated as "S1" in the figure; the same applies hereinafter), the engine water temperature TW detected by the water temperature sensor 23 is detected.
Is higher than a predetermined water temperature #TWINJ (for example, 80 ° C.). If the determination result is NO, the process proceeds to step 3 described later. On the other hand, when the determination result is YES and the engine 3 is in the high water temperature state, the process proceeds to step 2 and it is determined whether or not the idle flag F_IDLE is "1". The idle flag F_IDLE is set to "1" when the engine 3 is in the idle operation mode, and is set to "0" otherwise.

If the result of this determination is NO and the operating mode is other than the idle operating mode, the routine proceeds to step 3, where the engine water temperature TW is a predetermined lower limit water temperature # TWIS0 (predetermined temperature, for example 60
C)) is higher than the above. This determination result is NO
If the engine 3 is not sufficiently warm, the routine proceeds to step 4, where the injection end timing basic value THETI
NJX is set to the injection end timing #T for the predetermined low water temperature.
After setting to HETAjk, step 7 in FIG. 5 described later.
Proceed to. Injection end timing #THE for this low water temperature
TAjk (first timing) is set at a crank angle of 5 °, and the reason will be described below.

First, for the reasons described above, the engine water temperature T
Injection end timing THETAINJ when W is low
Is the distance DA between the end point and the crank angle CA2 position from the intermediate crank angle CA2 position between the start point (corresponding to the crank angle CA1) and the end point (corresponding to the crank angle CA3) of the buffer curve portion CINS. The crank angle is preferably set within the crank angle range (CA2 to CA4) up to the crank angle CA4 position. That is, the injection end timing TH
When ETAININ is set to the front side of the intermediate crank angle CA2 position, the valve lift amount of the intake valve 4 is considerably small and the mass flow velocity of the intake air is extremely small, so that the amount of fuel adhering to the wall surface of the intake port increases. Will end up. Further, the crank angle CA that exceeds the injection end timing THETAINJ by the distance DA from the end point of the buffer curve portion CINS.
If it is set to the rear side of the 4th position, the valve lift amount of the intake valve 4 is considerably large and the mass flow velocity of the intake air is large, so that the fuel that is not atomized is rapidly carried into the combustion chamber,
The amount of fuel adhering to the wall surface increases.

FIG. 6 shows the result of a measurement test conducted to confirm the above. Specifically, in the engine 3, when the engine water temperature TW is equal to or lower than the lower limit water temperature # TWIS0, the cam phase CAIN is set to the predetermined cam phase CAI.
With the fuel injection time TOUT held at N0 and the fuel injection time TOUT held at a constant value, a plurality of different injection end timings THET
The result of measuring the HC concentration in the exhaust gas with respect to AINJ is shown. As shown in the figure, the HC concentration changes from the crank angle −19 ° position (the position corresponding to the crank angle CA2 position) with the injection end timing THETAINJ as the center to the crank angle 19 ° position (the crank angle CA4 position). It was confirmed that the value becomes lower when the crank angle is within the corresponding range (up to the corresponding position), becomes the lowest when the crank angle is 5 °, and increases the HC concentration when the crank angle is outside the range. .

Therefore, the injection end timing # for low water temperature used when the engine 3 is not sufficiently warmed #
It is optimal to set THETAjk to a value within the crank angle range from the crank angle −19 ° position to the crank angle 19 ° position, and in the present embodiment, it is set to the crank angle 5 ° position where the HC concentration is the lowest. Has been done.

On the other hand, when the determination result of step 3 is YES, that is, when TW># TWIS0, the routine proceeds to step 5, where it is determined whether or not the throttle valve fully open flag F_THWOT is "1". This throttle valve fully open flag F_THWOT indicates that the throttle valve opening sensor 21
When the throttle valve opening degree θTH detected by is almost fully open, that is, in the throttle valve fully open mode, it is set to "1", and when not, it is set to "0".

When the result of this determination is NO, that is, when the throttle valve fully open mode is not set, the routine proceeds to step 6, where the basic value THETINJX of the injection end timing is set to
Injection end timing #THETAI for predetermined high water temperature
Set to JK, and then proceed to step 7 of FIG. 5 described later. Injection end timing #THETA for high water temperature
IJK (second timing) is set at a crank angle of 105 °, and the reason will be described below.

First, for the reasons described above, the engine water temperature T
Injection end timing THEAINJ when W is high
Is preferably set within a predetermined crank angle range (CA5 to CA7) including the crank angle CA6 position where the valve lift amount of the intake valve 4 is maximum. That is, if the fuel injection is performed at a timing other than this, the fuel injection will be performed except when the mass velocity of the intake air is at or near the maximum, which causes fuel to adhere to the wall surface of the intake port and May not produce a homogeneous mixture.

FIG. 7 shows the result of a measurement test conducted to confirm the above. Specifically, in the engine 3, when the engine water temperature TW is higher than the lower limit water temperature # TWIS0, the cam phase CAIN is set to the predetermined cam phase C.
With the fuel injection time TOUT held at AIN0 and the fuel injection time TOUT held at a constant value, a plurality of different injection end timings TH are set.
The measurement result of measuring the HC concentration in the exhaust gas is shown for ETAINJ. As shown in the figure, the HC concentration is such that the injection end timing THETAINJ is from the crank angle 95 ° position (the position corresponding to the crank angle CA5) to the crank angle 115 ° (the position corresponding to the crank angle CA7).
Becomes lower in the crank angle range up to, especially at the crank angle 105 ° position (position corresponding to crank angle CA6)
It was confirmed that it became the lowest at.

Therefore, the injection end timing #T for high water temperature used when the engine 3 is sufficiently warmed up
It is optimal to set HETAIJK to a value within the crank angle range from the crank angle 95 ° position to the crank angle 115 ° position. In the present embodiment, the valve lift amount of the intake valve 4 becomes the maximum value. The crank angle is set to 105 ° where the HC concentration is the lowest.

Next, FIG. 5 following step 4 or 6
In step 7 of the above, the basic value THETINJX calculated in step 4 or 6 is the previous value T of the injection end timing.
It is determined whether HETAINJ (n-1) or more. When the result of this determination is YES, the routine proceeds to step 8, where a predetermined addition item # is added to the previous value THETAINJ (n-1).
Value obtained by adding DTAINJ1 (for example, crank angle 5 °) (THETAINJ (n-1) + # DTAINJ1)
Is the current value of the injection end timing THETAINJ
Set as (n).

Next, in step 9, the basic value THET
The current value THETAIN calculated by INJX in step 8
It is determined whether or not J (n) or more. When the result of this determination is NO, the routine proceeds to step 10, where the basic value THET
INJX is set as the current value THETAINJ (n), and then the process proceeds to step 16 described later.

On the other hand, if the decision result in the step 9 is YES,
When THETINJX ≧ THETAINJ, step 10 is skipped and the process proceeds to step 16 described later.

On the other hand, if the determination result in step 7 is NO, T
When HETINJX <THETAINJ (n-1), the routine proceeds to step 11, where the previous value THEAINJ (n
The value (THETAINJ (n-1)) obtained by subtracting the predetermined subtraction term # DTAINJ2 (for example, crank angle 5 °) from -1).
-# DTAINJ2) is set as the current value THETAINJ (n) of the injection end timing.

Next, in step 12, the basic value THE
This time THETA calculated by TINJX in step 11
It is determined whether or not INJ (n) or less. When the result of this determination is NO, the routine proceeds to step 13, where the basic value TH
ETINJX is set as the current value THETAINJ (n), and then the process proceeds to step 16 described later. On the other hand, when the determination result is YES, step 13 is skipped and the process proceeds to step 16 described later.

By executing the above steps 3 to 13, when the determination result of step 3 does not change, the basic value THETINJX of the injection end timing is set to the previous value T.
By being equal to HETAINJ (n-1), the basic value THETINJX is set as it is as the current value THETAINJ (n) of the injection end timing. That is, the injection end timing is maintained.

On the other hand, when the determination result of step 3 is switched from NO to YES in this routine, that is, when the engine water temperature TW crosses the lower limit water temperature # TWIS0 and becomes higher than this, the basic value THETINJX is set.
However, the injection end timing for the low water temperature #THETAjk
To injection end timing for high water temperature #THETAIJ
The setting is switched to K, and the current value THETAINJ (n) of the injection end timing is the predetermined addition item #DTA.
INJ1 is set to increase gradually. That is,
The injection end timing is gradually changed to the retard side.

On the contrary, when the determination result of step 3 is changed from YES to NO in this routine, that is, when the engine water temperature TW crosses the lower limit water temperature # TWIS0 and becomes lower than this value, the basic value THETINJ
X is the injection end timing #THETAI for high water temperature
Injection end timing #THETA for low water temperature from JK
The current value THETAINJ (n) at the injection end timing is set to the predetermined subtraction item #DT while being set to jk.
AINJ2 is set to decrease gradually. That is, the injection end timing is gradually changed to the advance side.

In step 16 following any of steps 9, 10, 12 and 13, the addition correction term DINJCAI is calculated by searching the table shown in FIG. 8 according to the cam phase CAIN.

In the figure, the addition correction term DINJCAI is
The cam phase CAIN is set to a larger value as the cam angle CAIN is on the retard side, and when the cam phase CAIN is the predetermined cam phase CAIN0 as a boundary point, a positive value is set on the retard side and a advancing side is set. Is set to a negative value. This is set based on the valve lift curve of the intake valve 4 when the injection end timings #THETAjk, #THETAJJK for low water temperature and high water temperature are set when the cam phase CAIN is the predetermined cam phase CAIN0. Therefore, when the cam phase CAIN is controlled to the retard side or the advancing side with respect to the predetermined cam phase CAIN0, the valve lift curve of the intake valve 4 also shifts to the retarding side or the advancing side. Current value TH of injection end timing
This is because it is necessary to correct ETAINJ (n).

Next, in step 17, the calculated current value THETAINJ (n) is added to the addition correction term DINJCAI calculated in step 16 (THETAI).
After setting NJ (n) + DINJCAI) as the final injection end timing THETAINJ, this processing is ended.

On the other hand, if the decision result in the step 5 is YES, that is, if the throttle valve fully open mode, the routine proceeds to a step 14, where the current value THET of the injection end timing is set.
AINJ (n) is set to a predetermined value #THETAITH (for example, a crank angle of 45 ° position) for the throttle valve fully open mode, and then steps 16 and 17 are executed, and then this processing is ended.

On the other hand, when the result of the determination in step 2 is YES, that is, when the engine is in the idle operation mode, the routine proceeds to step 15, where the current value THETAI of the injection end timing is set.
NJ (n) is a predetermined value for the idle operation mode #THE
It is set to TAIDL (for example, a crank angle of 105 °), and after executing steps 16 and 17, this process is terminated.

As described above, according to the fuel injection control device 1 of the present embodiment, the engine water temperature TW is low and the engine 3
Is not sufficiently warmed, the injection end timing THETAINJ is set to be in the early stage of the intake stroke, so unlike the conventional case where fuel injection is performed at a time other than the intake stroke, the intake air flow into the intake pipe 11 is increased. By performing the fuel injection in the presence of the fuel gas, the atomization of the fuel can be promoted and the amount of the fuel adhering to the wall surface of the intake port can be further reduced. Furthermore, by injecting fuel at the timing of the early stage of the intake stroke, where the flow velocity of the intake air is relatively low, it is possible to accelerate the atomization of the fuel to some extent and then supply it to the combustion chamber. As described above, the fuel can be burned in a better combustion state, and the exhaust gas characteristics can be improved by reducing the HC concentration in the exhaust gas. In addition, at the time of sudden acceleration, etc., the fuel amount set according to the actual change of the intake air amount can be appropriately supplied to the combustion chamber, thereby suppressing the fluctuation of the air-fuel ratio to the lean side and being substantially appropriate. A good air-fuel ratio can be secured.

When the engine water temperature TW is high and the engine 3 is sufficiently warmed up, the injection end timing THETAINJ is the injection end timing #THETA for high water temperature at which the valve lift amount of the intake valve 4 becomes the maximum value.
Since it is set to IJK, it is possible to generate a more homogeneous air-fuel mixture while avoiding the adhesion of fuel to the wall surface of the intake port as much as possible. As a result, a good combustion state can be ensured and exhaust gas characteristics can be improved.

Further, the engine water temperature TW is the lower limit water temperature #T.
When it changes across WIS0, the injection end timing THETAINJ gradually increases to the retard side or the advance side,
Since it is changed, the transition can be performed smoothly without causing a sudden change in the air-fuel ratio. Thereby, good drivability can be secured and stable exhaust gas characteristics can be obtained.

In the embodiment, the injection end timing #THETAjk for low water temperature is set to the crank angle 5 ° position, but the invention is not limited to this, and the crank angle may be changed from the crank angle −19 ° (crank angle CA2) position to the crank angle. It may be set to a value within the crank angle range up to the 19 ° (crank angle CA4) position. When the intake cam of the engine has a cam profile different from that of the embodiment, the injection end timing #THETAjk for low water temperature is set between the start point and the end point of the buffer curve portion of the valve lift curve of the intake valve. From the crank angle position in the middle of, the distance between the end point and the intermediate position,
It may be set to a value within the crank angle range up to the crank angle position beyond the end point.

Further, in the embodiment, the injection end timing #THETAIJK for high water temperature is set to a crank angle of 105 °, but not limited to this, the injection end timing #THETAJJK for high water temperature is set to a crank angle of 95 °. It may be set to a value within the crank angle range from the (crank angle CA5) position to the crank angle 115 ° (crank angle CA7) position. Further, when the intake cam of the engine 3 has a cam profile different from that of the embodiment, the injection end timing #THETAIJK for high water temperature is set to the crank angle position where the valve lift amount of the intake valve 4 becomes the maximum value. The value may be set to a value within a predetermined crank angle range including that range. Also, the injection end timing #TH for high water temperature
The ETAIJK may be corrected according to the engine speed NE, and the corrected injection end timing #THETAJJK for high water temperature may be set as the basic value THETINJX of the injection end timing in step 6.

Furthermore, the fuel injection control device 1 of the present invention is
Needless to say, the invention may be applied to an internal combustion engine that does not include the cam phase changing mechanism 8. In that case, steps 16 and 17 of FIG. 5 of the embodiment are omitted, and the fuel injection end timing #THETAjk for low water temperature is
Set the timing within the crank angle range from the intermediate crank angle position between the start point and the end point of the buffer curve part of the valve lift curve to the crank angle position beyond the end point by the interval between the end point and the intermediate position. To be done. Further, the injection end timing #THETAIJK for high water temperature is set to a value within a predetermined crank angle range including the crank angle position where the valve lift amount of the intake valve 4 has the maximum value.

[0060]

As described above, according to the fuel injection control device for an internal combustion engine of the present invention, when the engine temperature is low,
It is possible to secure a good combustion state and a substantially proper air-fuel ratio, thereby improving the exhaust gas characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a fuel injection control device according to an embodiment of the present invention and an internal combustion engine to which the fuel injection control device is applied.

FIG. 2 is a diagram showing a valve lift curve of an intake valve and an exhaust valve of an internal combustion engine.

FIG. 3 is an enlarged view of a part of FIG.

FIG. 4 is a flowchart showing a calculation process of an injection end timing THETAINJ.

FIG. 5 is a flowchart showing a continuation of FIG.

FIG. 6 is an injection end timing THETAIN when the water temperature is low.
It is a figure which shows an example of the measurement result of HC density | concentration in exhaust gas when J is changed.

FIG. 7: Injection end timing THETAIN at high water temperature
It is a figure which shows an example of the measurement result of HC density | concentration in exhaust gas when J is changed.

FIG. 8 is a diagram showing an example of a table used to calculate an addition correction term DINJCAI.

[Explanation of symbols]

1 Fuel injection control device 2 ECU (injection end timing setting means, timing change setting means) 3 Internal combustion engine 4 Intake valve 6a Intake cam (cam) 23 Water temperature sensor (engine temperature detecting means) CIN Intake valve lift curve CINS Intake valve Cylinder angle position CA1 of the starting point of the buffer curve portion CA2 Intermediate crank angle position CA3 between the start point and the end point of the buffer curve portion CA3 Crank angle position DA of the end point of the buffer curve portion DA End point of the buffer curve portion Between the crank angle position and the intermediate crank angle position CA4 The crank angle position CA6 that exceeds the end point of the buffer curve portion and the intermediate crank angle position by the distance between the end point and the crank angle position CA5 at which the valve lift amount of the intake valve becomes the maximum value. CA7 Crank angle range THETAINJ in the vicinity including the crank angle position where the valve lift amount of the intake valve is maximum End timing of fuel injection #THETAjk Injection end timing for low water temperature (first timing) #THETAJJK Injection end timing for high water temperature (second timing) TW Engine water temperature (engine temperature) TWIS0 Predetermined lower limit water temperature (predetermined temperature) )

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidenobu Kotake             1-4-1 Chuo Stock Market, Wako City, Saitama Prefecture             Inside Honda Research Laboratory (72) Inventor Hiroshi Ito             1-4-1 Chuo Stock Market, Wako City, Saitama Prefecture             Inside Honda Research Laboratory F term (reference) 3G016 AA02 AA08 AA19 BA35 BA38                       BA40 DA01 DA06 DA22 GA06                       GA07 GA10                 3G084 BA15 BA23 CA01 CA02 DA02                       DA04 DA10 EB08 EB12 FA10                       FA11 FA20 FA38 FA39                 3G301 HA01 HA06 HA19 JA02 JA23                       JA26 KA01 KA02 KA07 LB02                       LC01 MA20 NA07 NB06 NC02                       ND04 NE11 NE12 PA07Z                       PA11Z PB05A PE01Z PE03Z                       PE04Z PE08Z PE10A

Claims (3)

[Claims] 1. A fuel injection control device for an internal combustion engine, which opens and closes an intake valve by a cam having a cam profile that produces a valve lift curve having a buffer curve portion in the initial stage of valve opening and injects fuel into an intake port of a cylinder. When the detected engine temperature is equal to or lower than a predetermined temperature, the end timing of the fuel injection is defined as a start point and an end point of the buffer curve portion. Injection end timing setting for setting the first timing within the crank angle range from the intermediate crank angle position between the end point and the intermediate crank angle position to the crank angle position beyond the end point by the interval between the end point and the intermediate crank angle position. A fuel injection control device for an internal combustion engine, comprising: 2. The injection end timing setting means includes, when the engine temperature is higher than the predetermined temperature, the fuel injection end timing including a crank angle position at which the valve lift amount of the intake valve reaches a maximum value. The fuel injection control device for an internal combustion engine according to claim 1, wherein the second timing is set within a predetermined crank angle range in the vicinity thereof. 3. The injection end timing setting means, when the engine temperature changes across the predetermined temperature,
3. The fuel injection control of an internal combustion engine according to claim 2, further comprising timing changing means for gradually changing the end timing of the fuel injection from one of the first and second timings toward the other. apparatus.