JP2009185771A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve startability, particularly when using fuel is a heavy quality, in an internal combustion engine having a fuel injection valve with respective cylinders in an intake passage. <P>SOLUTION: This fuel injection control device of the internal combustion engine has the fuel injection valve with respective cylinders in the intake passage. While performing a first quantity increase correction of a fuel injection quantity when an increase degree of an engine speed does not reach a first threshold value until a first predetermined time passes from the beginning of starting (S1-S5, S10 and S11), when the increase degree of the engine sped reaches the first threshold value until the first predetermined time passes from the beginning of starting, a second quantity increase correction is performed when the increase degree does not reach a second threshold value (> the first threshold value) (S1-S6, S7 and S8). An increase quantity of fuel by the first quantity increase correction is set smaller than an increase quantity of the fuel by the second quantity increase correction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection amount control device for an internal combustion engine that performs an increase correction of the fuel injection amount at and after the start.

Patent Document 1 describes that the amount of fuel supply is corrected to be increased when it is determined that the property of the fuel supplied to the engine at the time of starting is heavy.
Japanese Patent Laid-Open No. 5-156983

According to the above prior art, it is possible to suppress a decrease in the amount of fuel flowing into the cylinder (that is, the fuel actually used for combustion) when heavy fuel having a low vaporization rate is used.
However, if, for example, the cranking time is long and the fuel supply amount increase correction is performed based on the fuel heavyness determination, the cylinder will be over-rich due to the fuel accumulated so far, and the rotation will slow down. And may cause a rich engine.

  An object of the present invention is to improve the startability particularly when the fuel used is heavy.

  In the fuel injection control device for an internal combustion engine having a fuel injection valve for each cylinder in the intake passage, the present invention sets the degree of increase in the engine rotational speed to the first threshold value until the first predetermined time elapses from the start of starting. When the fuel injection amount is not reached, the first increase correction of the fuel injection amount is performed. On the other hand, the increase degree of the engine speed reaches the first threshold from the start of the engine until the first predetermined time elapses. When the second threshold value larger than the first threshold value is not reached, the second increase correction of the fuel injection amount is performed, and the fuel increase amount (or fuel increase rate) by the first increase correction is set to the second increase amount. It is made smaller than the amount of fuel increase (or fuel increase rate) by correction.

It has been confirmed that there is a large difference in the degree of increase in engine speed at start-up depending on the properties of the fuel used (light and heavy).
According to the fuel injection control device for an internal combustion engine according to the present invention, it is possible to suppress a decrease in the amount of fuel flowing into the cylinder, particularly when the properties of the fuel used are heavy. It is possible to suppress over-richness of the air-fuel ratio due to the fuel remaining as a wall flow in the intake port flowing into the cylinder when it is slow (bad). As a result, the startability can be improved particularly when heavy fuel is used.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an internal combustion engine (four-cylinder engine, hereinafter simply referred to as “engine”) showing an embodiment of the present invention.

  A combustion chamber 2 of each cylinder of the engine 1 is defined by a piston 3. An ignition plug 4 for igniting the air-fuel mixture in the combustion chamber 2 is provided at an approximately central portion above the combustion chamber 2, and an intake valve 5 and an exhaust valve 6 are provided so as to surround the ignition plug 4.

  The intake passage 7 is provided with a throttle valve 8 on the upstream side of the intake manifold, and electromagnetic fuel injection is performed for each cylinder in each branch portion of the intake manifold (a position facing the intake port on the cylinder head side). A valve 9 is provided. The fuel injection valve 9 injects fuel toward the valve head portion of the intake valve 5. The injected fuel is mixed with intake air (fresh air) and sucked into the combustion chamber 2 through the intake valve 5.

The combustion exhaust is discharged to the exhaust passage 10 through the exhaust valve 6. An exhaust purification catalyst 11 is provided in the exhaust passage 10.
The engine control unit (ECU) 20 inputs detection signals from various sensors, performs predetermined arithmetic processing, and controls the operation of the fuel injection valve 9 and the spark plug 4. As the various sensors, an air flow meter 21 for detecting the intake air amount Qa upstream of the throttle valve 8, a cam angle sensor 22 for cylinder discrimination, and a crank angle signal are output in synchronism with engine rotation. A crank angle sensor 23 capable of detecting the engine rotational speed Ne, a water temperature sensor 24 for detecting the engine cooling water temperature Tw, and the like are also provided.

The fuel injection control by the ECU 20 is performed as follows.
That is, the basic fuel injection amount Tp = K · Qa / Ne (K is a constant) is calculated based on the intake air amount Qa and the engine rotational speed Ne, and various corrections are made on this to obtain the final fuel injection amount Ti = Tp. COEF (COEF is various correction coefficients) is calculated, and a drive pulse signal having a pulse width corresponding to the calculated Ti is output to the fuel injection valve 9 of each cylinder at a predetermined timing.

Here, the various correction coefficients COEF include an increase correction coefficient (hereinafter referred to as “post-startup increase correction coefficient”) KAS for fuel increase at the start and after the start, as in the following equation.
COEF = 1 + KAS + ...
Further, the post-startup increase correction coefficient KAS is normally calculated by the following equation (1).

KAS = MTKAS × TMKAS (1)
Here, MTKAS is a table value (water temperature increase rate) corresponding to the engine coolant temperature Tw, and is large when the water temperature is low and becomes small as the water temperature increases. In addition, this MTKAS is adapted by, for example, the upper limit value of the central fuel in the market (fuel property: T50 = 100 ° C.). Further, TMKAS is a table value (time correction coefficient) corresponding to the elapsed time after startup, and becomes a smaller value as time elapses.

Hereinafter, the start control executed by the ECU 20 in the present embodiment will be described.
As described above, the ECU 20 increases and corrects the fuel injection amount at the start and after the start. In particular, in the present embodiment, the amount of fuel flowing into the cylinder is determined by determining the property (heavy) of the fuel used at start-up, and when determining that the fuel is heavy, further increasing the fuel injection amount. Suppresses the decrease in The increase correction in the case of heavy fuel is basically performed by adding the heavy increase rate HTKAS when calculating the post-startup increase correction coefficient KAS, as will be described later.

FIG. 2 is a flowchart of a routine for setting the property (heavy and light) of the fuel used and setting an increase correction coefficient KAS after starting. As described above, the engine of this embodiment has four cylinders.
In FIG. 2, in step S1, the initial injection cylinder is determined.

  The ECU 20 performs cylinder discrimination to determine which stroke each cylinder is in order to perform fuel injection for each cylinder, and then performs fuel injection to each cylinder, and starts starting based on this cylinder discrimination result. The first fuel injection is specified from (start cranking), and the cylinder is determined as the first injection cylinder. When the first injection cylinder is determined, “Nc” indicating the number of cylinders from the first fuel injection cylinder is set to 1.

  Here, the fuel injection is normally performed in the exhaust stroke of each cylinder. However, in order to start more quickly, the fuel injection is performed in the intake stroke for the initial injection cylinder (Nc = 1). Yes. For this reason, the fuel injection into the first injection cylinder (Nc = 1) and the fuel injection into the second injection cylinder (Nc = 2) are simultaneously performed.

  In step S2, the angular acceleration Δω of the crank rotation as the degree of increase in the rotational speed for the first injection cylinder (Nc = 1) is calculated. The angular acceleration Δω is calculated by detecting the angular velocity ω1 (deg / s) at the compression top dead center (TDC) and the maximum angular velocity ω2 (deg / s) in the expansion stroke, and calculating the angular acceleration Δω (= ω2) from these angular velocities. -Ω1) is calculated. More precisely, Δω = (ω2−ω1) / dt may be calculated. Note that dt is the time from the detection of ω1 to the detection of ω2. However, the method is not limited to the method shown here, and the degree of increase in rotational speed or the angular acceleration Δω may be calculated by other methods.

  Note that the maximum angular velocity ω2 in the expansion stroke is calculated by, for example, a subroutine shown in FIG. The subroutine of FIG. 3 is executed after detecting the angular velocity ω1 at the time of compression top dead center (TDC). First, ωmax is initialized (ωmax = 0) (step S21), and the angular velocity ω is detected at a predetermined sampling interval (for example, every crank angle of 10 °) (step S22). Then, the detected angular velocities ω and ωmax are compared (step S23). If ω> ωmax, ωmax is updated with ωmax = ω (step S24). Then, it is determined whether or not the bottom dead center (BDC) at or near the end of the expansion stroke is reached (step S25), and if not BDC (near), the sampling process and the ωmax update process are continued. When BDC (near) is reached, ωmax at that time is set as the maximum angular acceleration ω2 in the expansion stroke (step S26).

  In step S3, an initial explosion (start) determination is performed. The initial explosion determination is performed by comparing the angular acceleration Δω calculated as the degree of increase in the rotational speed of each cylinder with a predetermined initial explosion determination threshold ΔωS (corresponding to the “first threshold” of the present invention). When the calculated angular acceleration Δω reaches the initial explosion determination threshold value ΔωS, that is, when Δω ≧ ΔωS, it is determined that the first explosion has occurred. If Δω ≧ ΔωS, the process proceeds to step S4. The initial explosion determination threshold value ΔωS is set to a value larger than the angular acceleration Δω during cranking (motoring).

  In step S4, it is determined whether or not Nc = 4 (fourth from the first injection cylinder, that is, the last injection cylinder in the first round in the case of four cylinders). If Nc = 4 (the last injection cylinder in the first round), the routine proceeds to step S5, where the number of cylinders Nc is increased by one. In step S2, the angular acceleration Δω is calculated for the next injection cylinder, and the angular acceleration Δω calculated in step S3 is compared with the initial explosion determination threshold value ΔωS.

  More specifically, during the period when the fuel injection into each cylinder is completed from the start of the start, more specifically, until the end of the expansion stroke of the last injection cylinder in the first round ("until the first predetermined time elapses in the present invention" If Δω ≧ ΔωS, the process proceeds to step S6.

  In step S6, heavy / lightness determination of the used fuel is performed. The heavy / lightness determination is performed by comparing the angular acceleration Δω with a predetermined heavy / lightness determination threshold value ΔωL (corresponding to the “second threshold value” of the present invention). In this case, it is natural that the angular acceleration Δω ≧ the initial explosion determination threshold value ΔωS, and the heavy / lightness determination threshold value ΔωL> the initial explosion determination threshold value ΔωS.

  Then, if Δω ≧ ΔωL, the process proceeds to step S7, where it is determined that the property of the fuel used is “light” (in other words, the fuel property is comparable to the above-mentioned compatible fuel (market center fuel)). End the flow. In this case, the post-startup increase correction coefficient KAS is calculated by the above equation (1), and the fuel injection amount is corrected to be increased. Such increase correction of the fuel injection amount corresponds to “third increase correction” of the present invention.

On the other hand, if Δω <ΔωL, the routine proceeds to step S8, where it is determined that the property of the fuel used is “heavy”, and in step 9, the post-startup increase correction coefficient KAS is calculated by the following equation (2).
KAS = (MTKAS + HTKAS) × TMKAS (2)
Here, HTKAS is a fuel increase amount (heavy increase rate) in the case of heavy fuel. Although this HTKAS may be a constant value, it is preferably set as a table value corresponding to the engine coolant temperature Tw, similarly to MTKAS. This is because the difference in fuel vaporization rate between heavy fuel and light fuel tends to increase at low water temperatures. In this case, HTKAS is large when the water temperature is low, and decreases as the water temperature increases.

  Heavy fuel with a low vaporization rate is injected and much of the fuel remains as a wall flow in the intake port as compared with light fuel, and the amount of fuel flowing into the cylinder is reduced. Therefore, the heavy increase rate HTKAS is added when calculating the post-startup increase correction coefficient KAS, and the increase in the fuel injection amount in the case of heavy fuel is corrected, thereby suppressing the decrease in the amount of fuel flowing into the cylinder. Such increase correction of the fuel injection amount corresponds to “second increase correction” of the present invention.

  If “YES” in the step S4, that is, if the initial explosion determination is not made within the first round, the process proceeds to a step S10 to determine that the property of the used fuel is “super heavy”, and the engine is started in the step S11. The post-increase correction coefficient KAS is calculated by the following equation (3).

KAS = (MTKAS + HTKAS−DHKAS) × TMKAS (3)
Here, DHKAS is a fuel reduction rate for reducing the increase in fuel in the case of heavy fuel when it is determined that the fuel used is super heavy, and basically HTKAS ≧ DHKAS.

  If the first explosion determination is not made within the first round, it is considered that not only the property of the fuel used is “heavy” but also the vaporization rate is worse. In the present embodiment, the fuel property in such a state is determined as “super heavy”. For example, when heavy fuel that has been left for a long period of time is used, it may be determined to be “super heavy”.

  Further, since a large amount of fuel is injected by the first round of fuel injection, and the initial explosion has not been reached, a large amount of fuel remains as a wall flow in the intake port. If further increase correction of the fuel is performed in this state, the wall flow is vaporized and flows into the cylinder, resulting in over-richness, which may cause the rotational speed to drop or rich-end. On the other hand, since the fuel property is “heavy” (ultra-heavy), if the increase correction in the case of heavy fuel is completely stopped, the decrease in the amount of fuel flowing into the cylinder immediately after injection will be sufficiently reduced. May not be able to be suppressed. For this reason, in this embodiment, when the initial explosion determination is not made during the round of fuel injection to each cylinder from the start of the start, it is determined that a relatively large amount of fuel remains (is accumulated) as a wall flow. Then, by subtracting the heavy increase rate HTKAS by the fuel decrease rate DHKAS, the fuel increase amount is further reduced to prevent the fuel amount flowing into the cylinder from being excessive or insufficient.

Thereafter, the process proceeds to step S12, and the cylinder number Nc is increased by one.
In step S13, as in step S2, the angular acceleration Δω is calculated for Nc = 5 (the fifth cylinder from the first injection cylinder, that is, the first injection cylinder in the second round from the start of the start).

  In step S14, the initial explosion determination is performed as in step S4. That is, the angular acceleration Δω calculated in step S14 is compared with the initial explosion determination threshold value ΔωS. If Δω <ΔωS, the process proceeds to step S15.

  In step S15, it is determined whether or not Nc = 8 (the eighth cylinder from the first injection cylinder, that is, the last injection cylinder in the second round from the start). If Nc = 8 (the last injection cylinder in the second round), the process returns to step S12 and Nc is increased by 1. In step S13, the angular acceleration Δω is calculated for the next cylinder, and in step S14, the initial explosion determination threshold value ΔωS is obtained. Compare.

  As a result, the fuel injection into each cylinder is started twice from the start of the start, more specifically, until the expansion stroke of the last injection cylinder in the second round is completed (“second” of the present invention If Δω ≧ ΔωS is satisfied) until the predetermined time elapses, this flow ends.

  On the other hand, if Δω ≧ ΔωS is not satisfied for all the cylinders in the second round, the process proceeds to step S16 and the post-startup increase correction coefficient KAS is set to zero. As a result, not only fuel increase in the case of heavy fuel (HTKAS), but also fuel increase based on engine coolant temperature (MTKAS) is prohibited.

  If the first explosion is not judged within the second round, more fuel remains as a wall flow in the intake port, so the rotational speed drops due to the over-richness caused by this wall flow, or the engine is rich. More likely. Therefore, the fuel injection amount increase correction itself is prohibited.

In this case, since it is considered that the combustion is difficult, in step S17, the ignition timing is corrected to the advance side, and this flow is finished.
The increase in fuel injection amount for heavy fuel is reduced by the post-startup increase correction coefficient KAS calculated in step S11, and the fuel injection amount increase is corrected by the post-startup increase correction coefficient KAS calculated in step S16. However, the ECU 20 is also executing idle speed control. For example, when the feedback correction amount of ignition feedback in the idle speed control is reversed, the ECU 20 decreases the fuel injection amount and increases the fuel. The prohibition of the increase correction of the injection amount is canceled, that is, the post-startup increase correction coefficient KAS is calculated by the above equation (2).

  With the above control, in this embodiment, all the cylinders are started during the period from the start to the end of fuel injection to each cylinder (more specifically, until the expansion stroke of the last injection cylinder in the first round is completed). When the angular acceleration Δω of the crank rotation, which is the degree of increase in rotational speed, does not exceed the initial explosion determination threshold ΔωS, the post-startup increase correction coefficient KAS = (MTKAS + HTKAS−DHKAS) × TMKAS, and the post-startup increase correction coefficient KAS Based on this, the fuel injection amount increase correction is performed.

  On the other hand, when the acceleration Δω is equal to or greater than the initial explosion determination threshold ΔωS for any cylinder but does not exceed the heavy / light determination threshold ΔωL, the post-startup increase correction coefficient KAS = (MTKAS + HTKAS) × TMKAS is set. An increase correction of the fuel injection amount is performed based on the correction coefficient KAS.

  Then, during the period from the start of the start until the fuel injection into each cylinder makes two rounds (more specifically, until the expansion stroke of the last injection cylinder in the second round ends), the degree of increase in rotational speed for all the cylinders. When the angular acceleration Δω of crank rotation does not exceed the initial explosion determination threshold value ΔωS, the post-startup increase correction coefficient KAS = 0, and the fuel increase of the fuel injection amount is prohibited.

FIG. 4 is a time chart of the start control, where (a) shows the engine speed, (b) the ignition timing, (c) the fuel increase rate, and (d) the air-fuel ratio A / F.
When the initial explosion is reached (T1) from the start to the end of fuel injection to each cylinder (T1), and subsequently it is determined that the property of the fuel used is “heavy” (time t1), the heavy increase The fuel increase correction for heavy fuel is performed by the rate HTKAS (see equation (2)). In this case, the engine speed, ignition timing, fuel increase rate, and air-fuel ratio A / F are shown by solid lines. After the complete explosion, the engine rotation speed is controlled to the target idle rotation speed by idle rotation speed control.

  Here, it is determined that the property of the fuel used is “heavy” even when the first explosion cannot be reached during the period from the start of fuel injection to the completion of fuel injection to each cylinder (T1). However, in this case, it is determined that the “super-heavy” has a lower vaporization rate. At this time as well, fuel increase correction for heavy fuel is performed, but the heavy increase rate HTKAS is subtracted by the fuel decrease rate DHKAS (see equation (3)). In this case, the engine speed, ignition timing, fuel increase rate, and air-fuel ratio A / F are indicated by broken lines. In FIG. 4, when a predetermined time (T3) has elapsed (time t4), fuel injection into each cylinder has started two times from the start so that the fuel increase rate by the post-start increase coefficient KAS becomes zero. To adjust the time correction coefficient TMKAS.

  Then, if the first explosion cannot be reached during the period from the start of the start until the fuel injection to each cylinder makes two cycles (T2), the post-startup increase correction coefficient KAS = 0 is set at the start and after the start. The increase correction of the fuel injection amount is prohibited (time t2). In this case, the engine speed, the ignition timing, the fuel increase rate, and the air-fuel ratio A / F are indicated by a one-dot chain line. In addition, the ignition timing is corrected to the advance side in order to make it easy to burn (time t3). The ignition timing is subsequently controlled within the hatched range in the figure by idle rotation speed control (ignition feedback).

  In the present embodiment, step S2 in FIG. 2 corresponds to the “detection means” of the present invention, step S10 corresponds to the “first correction means” of the present invention, and the process of step S9 is the “second correction” of the present invention. It corresponds to “means”. Step S7 corresponds to the “third correction means” of the present invention, step S16 corresponds to the “correction prohibition means” of the present invention, and step S17 corresponds to the “ignition timing correction means” of the present invention.

The present embodiment has the following effects.
In other words, the heavy / lightness determination of the used fuel is performed at the start, and the increase correction of the fuel injection amount is changed according to the determination result, so that even when heavy fuel is used, the decrease in the in-cylinder inflow fuel amount is suppressed. be able to.

  Also, when heavy fuel is used and the initial explosion is not judged between the start of fuel injection and the completion of fuel injection to each cylinder, the fuel injection amount for heavy fuel is increased. When the initial explosion determination is not made between the start of the start and the fuel injection to each cylinder twice, the increase of the fuel injection amount is prohibited, so that the fuel is accumulated in the intake port ( It can be suppressed that the amount of fuel flowing into the cylinder increases due to the remaining fuel, resulting in over-richness.

  In addition, if the initial explosion determination is not made between the start of fuel injection and the second round of fuel injection to each cylinder, the ignition timing is advanced. Yes (can be started reliably)

1 is a system diagram of an internal combustion engine according to an embodiment of the present invention. It is a flowchart of the setting routine of the property determination of the use fuel which concerns on embodiment, and the increase correction coefficient after a start. It is a flowchart of the maximum angular velocity detection subroutine of the expansion stroke. It is a time chart of starting control concerning an embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine (engine), 7 ... Intake passage, 9 ... Fuel injection valve, 20 ... ECU, 21 ... Air flow meter, 22 ... Cam angle sensor, 23 ... Crank angle sensor, 24 ... Water temperature sensor

Claims (10)

A fuel injection control device for an internal combustion engine having a fuel injection valve for each cylinder in an intake passage,
Detection means for detecting the degree of increase in engine speed;
First correction means for performing first increase correction of the fuel injection amount when the increase degree of the engine rotation speed detected by the detection means does not reach the first threshold value after the first predetermined time has elapsed from the start of the start. When,
When the degree of increase in the engine rotational speed detected by the detection means has reached the first threshold value from the start of starting until the first predetermined time has elapsed, the second threshold value is greater than the first threshold value. Second correction means for performing a second increase correction of the fuel injection amount when the threshold is not reached,
A fuel injection control device for an internal combustion engine, wherein an increase in fuel by the first increase correction is smaller than an increase in fuel by the second increase correction. A third increase correction of the fuel injection amount is performed when the increase degree of the engine speed detected by the detection means reaches the second threshold value from the start of the engine until the first predetermined time elapses; A correction means,
2. The fuel injection control device according to claim 1, wherein an amount of fuel increase by the third increase correction is smaller than a fuel increase amount by the first increase correction. 3.   In the case where the degree of increase in the engine speed detected by the detecting means does not reach the first threshold value from the start of the engine until the second predetermined time greater than the first predetermined time elapses, the fuel injection amount 3. The fuel injection control device for an internal combustion engine according to claim 1, further comprising correction prohibiting means for prohibiting the increase correction.   The fuel injection control device for an internal combustion engine according to any one of claims 1 to 3, wherein the detection means detects a degree of increase in rotational speed for each cylinder accompanying fuel injection.   The first correction means increases the first increase when the degree of increase in rotational speed of all cylinders from the first fuel injection cylinder at the start to the last fuel injection cylinder in the first round does not reach the first threshold. 5. The fuel injection control device for an internal combustion engine according to claim 4, wherein correction is performed.   The second correction means is a case where the degree of increase in rotational speed of any cylinder from the first fuel injection cylinder at the start to the last fuel injection cylinder in the first round reaches the first threshold value, 6. The fuel injection control device for an internal combustion engine according to claim 4, wherein the second increase correction is performed when the second threshold value is not reached.   The third correction means is configured to perform the third correction when the degree of increase in the rotational speed of any cylinder from the first fuel injection cylinder at the start to the last fuel injection cylinder in the first round reaches the second threshold. The fuel injection control device for an internal combustion engine according to any one of claims 4 to 6, wherein an increase correction is performed.   The correction prohibiting means controls the fuel injection amount when the increase in rotational speed of all cylinders from the first fuel injection cylinder at the start to the last fuel injection cylinder in the second round does not reach the first threshold value. The fuel injection control device for an internal combustion engine according to any one of claims 4 to 7, wherein the increase correction is prohibited.   The fuel injection control device for an internal combustion engine according to any one of claims 1 to 8, wherein the detection means detects an angular acceleration of crank rotation as an increase degree of the engine rotation speed.   Ignition timing correction that corrects the ignition timing to the advance side when the degree of increase in the engine speed detected by the detection means does not reach the first threshold value from the start of the engine until the second predetermined time has elapsed. The fuel injection control device for an internal combustion engine according to any one of claims 3 to 9, further comprising means.

Images