JP4055425B2 - Control device for direct-injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct injection spark ignition engine.
[0002]
[Prior art]
When the temperature of the cylinder wall surface and the piston surface is low, the vaporized fuel of the fuel supplied by injection burns, and the attached liquid fuel is heated and vaporizes and burns, but the liquid fuel that could not be vaporized is , It remains unburned at the site where it adheres, and carbonized and deposited. In addition to this, the same phenomenon occurs and accumulates in lubricating oil that is mixed in in a small amount. Such unburned deposits are called deposits (or deposits for short).
[0003]
In an engine that directly injects fuel into the cylinder with the injector facing the cylinder, deposit accumulation at the tip of the injector becomes a problem.
For this reason, in JP-A-10-274134 and JP-A-2000-227063, deposits are prevented from being deposited by adding another configuration such as devising the material and shape of the tip of the injector.
[0004]
Japanese Patent Laid-Open No. 9-151770 corrects a fuel injection amount that changes due to deposit accumulation on the tip of an injector.
[0005]
[Problems to be solved by the invention]
In a direct-injection spark-ignition engine, when deposits accumulate at the tip of the injector, the spread angle of the injected fuel changes, and the penetration force (penetration; reach distance) of the fuel spray also changes. Specifically, the spread angle of the injected fuel increases due to the Coanda effect by the deposit, and the penetration force of the fuel spray decreases.
[0006]
As a result, when the fuel injection timing is set in the initial state and the fuel is injected in the deteriorated state where deposits have accumulated, the ignition timing comes before the fuel reaches the spark plug. Cannot be realized, combustion stability is deteriorated, and emission is further deteriorated.
In addition, in JP-A-10-274134 and JP-A-2000-227063, since the deposit is prevented from being deposited by adding another configuration to the tip of the injector, the cost is increased and the complexity is further increased. There has been a problem of causing an increase in the failure frequency due to.
[0007]
Further, in the above-mentioned Japanese Patent Laid-Open No. 9-151770, since the fuel injection amount that changes due to deposit accumulation is corrected, the accuracy of the correction injection amount is required, and it is difficult to ensure sufficient accuracy. In addition, there was a problem that it was not possible to cope with changes in penetration of fuel spray.
In view of such circumstances, an object of the present invention is to provide a control device for a direct-injection spark ignition engine capable of realizing initial appropriate combustion regardless of deposits deposited on the tip of an injector. To do.
[0008]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, in a direct-injection spark-ignition engine including an injector that directly injects fuel into a cylinder and an ignition plug, a deposit amount estimation means that estimates the amount of deposit on the injector tip. In the stratified combustion in which fuel is injected in the compression stroke, at least one of the fuel injection timing and the ignition timing is corrected according to the estimated accumulation amount. When correcting and correcting the ignition timing, there is provided correction means for correcting a retard angle as the amount of accumulation increases .
[0009]
According to a second aspect of the present invention, the accumulation amount estimation means obtains an accumulation amount estimated value by cumulatively increasing with the passage of time of engine operation.
In this case, the degree of increase in the estimated accumulation amount may be changed according to the engine operating state. Further, the engine operating state that changes the degree of increase in the estimated amount of deposit is the temperature at the tip of the injector or a parameter related thereto (Claim 4), the presence or absence of fuel cut (Claim 5), the fuel injection timing (Claim). 6), fuel properties (Claim 7) and the like.
[0010]
The invention according to claim 8 is characterized in that the accumulation amount estimation means obtains the accumulation amount estimation value in proportion to the travel distance.
Further, the invention according to claim 9 is characterized in that an upper limiter is provided for the accumulation amount estimated value by the accumulation amount estimation means or the correction value by the correction means corresponding thereto.
[0011]
【The invention's effect】
According to the first aspect of the present invention, deposit accumulation at the tip of the injector causes the spread angle of the injected fuel to increase due to the Coanda effect by the deposit, the penetration force of the fuel spray decreases, and the fuel spray ignition Even if the time to reach the plug becomes longer, the initial appropriate combustion can be realized by the advance angle of the fuel injection timing and / or the retard angle of the ignition timing, and the exhaust performance can be ensured.
[0012]
According to the second aspect of the present invention, the deposit accumulation amount can be easily estimated by accumulatively increasing with the passage of time of engine operation and obtaining the accumulation amount estimation value.
According to the third aspect of the present invention, the accuracy of estimation can be improved by changing the degree of increase in the estimated amount of deposit according to the engine operating state, so as to correspond to the change in the deposit amount due to the engine operating state. .
[0013]
According to the invention of claim 4, by using the tip temperature of the injector or a parameter related thereto for estimation of the accumulation amount, the estimation accuracy is increased corresponding to the increase in deposit adhesion amount as the injector tip temperature is lower. Can be improved.
According to the invention of claim 5, by using the presence or absence of the fuel cut for the estimation of the accumulation amount, the estimation accuracy is improved in consideration of the fact that the temperature at the tip of the injector is lowered and the deposit is easily accumulated during the fuel cut. be able to.
[0014]
According to the invention of claim 6, by using the fuel injection timing for estimating the accumulation amount, the estimation accuracy is improved in consideration of an increase in the amount of deposit adhering to the injector tip at a specific fuel injection timing. be able to.
According to the invention of claim 7, by using the fuel property for estimation of the deposit amount, for example, gasoline fuel is composed of hydrocarbons of various compositions, and the deposit adhesion amount changes depending on the composition. As the amount of high boiling point components increases and the amount of deposits increases, it can be adapted to improve the estimation accuracy.
[0015]
According to the eighth aspect of the present invention, the deposit accumulation amount can be easily estimated by obtaining the accumulation amount estimated value almost in proportion to the travel distance.
According to the ninth aspect of the present invention, by providing the upper limiter with respect to the accumulation amount estimated value by the accumulation amount estimation means or the correction value by the correction means corresponding thereto, the deposit accumulation amount is saturated to a certain amount, that is, to some extent. Once deposited, it can be adapted to burn when its surface temperature increases.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of a direct-injection spark ignition engine showing an embodiment of the present invention. First, this will be described.
In the engine 1, the air controlled by the throttle valve 5 is sucked into the combustion chamber 3 of each cylinder defined by the piston 2 through the intake valve 6 through the intake passage 4.
[0017]
An injector (fuel injection valve) 7 that directly injects fuel into the combustion chamber 3 is provided so as to face the combustion chamber 3 of each cylinder from the intake valve 6 side. The fuel that has been sucked and discharged by the low-pressure fuel pump 9 disposed in the fuel tank 8 and further increased in pressure by the high-pressure fuel pump 10 is guided to the injector 7 in a state of being regulated by a pressure regulator (not shown). .
[0018]
Further, a spark plug 11 is provided facing the combustion chamber 3 of each cylinder from the center of the cylinder head.
Here, the operations of the injector 7 and the spark plug 11 are controlled by the control unit 12 for engine control.
The control unit unit 12 receives signals from various sensors for such control.
[0019]
As the various sensors, there are provided a crank angle sensor 13 capable of detecting the crank angle and detecting the engine speed Ne, an air flow meter 14 for detecting the intake air amount Qa, and a water temperature sensor 15 for detecting the engine water temperature Tw. . If necessary, an injector tip temperature sensor 16 for detecting the tip temperature T of the injector 7, a fuel property sensor 17 for detecting the fuel property (V), a mileage meter 18 for integrating the mileage D, and the like are provided.
[0020]
Based on these signals, the control unit 12 sets the fuel injection timing and the fuel injection amount, sets the ignition timing, and controls the operation of the injector 7 and the spark plug 11.
Here, in particular, under predetermined operating conditions (for example, low and medium load regions), fuel is injected into the combustion chamber 3 by the injector 7 in the compression stroke, so that it is stratified in the vicinity of the spark plug 11 in the combustion chamber 3. The mixture is controlled to perform stratified combustion. FIG. 2 shows compression stroke injection at the time of stratified combustion. The fuel spray injected from the injector 7 bounces off at the crown surface (cavity inner surface) of the piston 2 and is guided to the vicinity of the spark plug 11. It leads to ignition.
[0021]
Further, under other operating conditions (for example, a high load region), fuel is injected into the combustion chamber 3 by the injector 7 during the intake stroke, thereby forming an air-fuel mixture having a substantially uniform mixing ratio in the entire combustion chamber 3. Control to perform homogeneous combustion. Incidentally, there is shown schematically a fuel injection period of the fuel injection period and the stratified charge combustion during the homogeneous combustion in FIG.
Next, fuel spraying by the injector 7 in such a direct injection spark ignition engine will be considered.
[0022]
In the injector (especially the swirler type injector) 7, the fuel spray is injected into a hollow cone as shown in FIG.
In the compression stroke injection during stratified combustion, as shown in FIG. 3, since the cylinder pressure (atmospheric pressure) at the time of injection is high, the fuel spray is crushed, as shown in FIG. 4 (b). It becomes a shape.
[0023]
Therefore, at the time of stratified combustion, the injection timing and the ignition timing are set on the premise of the spray characteristics shown in FIG. 4B, that is, the spray spread angle θ1 and the spray penetration force (penetration; reaching distance) L1.
Under such a premise, the combustible combination of the injection timing and the ignition timing at the time of stratified combustion is within the range of A shown in FIG. As the injection timing is delayed, the ignition timing is delayed as long as the fuel spray characteristics are the same. As shown in FIG. 2, the time for the spray injected by the injector 7 to reach the spark plug 11 is approximately. This is because they are the same. Usually, it is set to a point a within the range A.
[0024]
However, when the engine is in operation, the incomplete combustion fuel gradually accumulates as deposits at the tip of the injector 7 as shown in FIG.
Accordingly, if deposits are accumulated in the compression stroke injection during stratified combustion, as shown in FIG. 4C, spray spreads due to the Coanda effect as compared to FIG. 4B (spray spread angle θ2> θ1). ), The spray penetration force (penetration; reach distance) decreases (L2 <L1).
[0025]
As a result, the time for the fuel spray from the injector 7 described with reference to FIG. 2 to reach the ignition plug 11 becomes longer, and the combination of combustible injection timing and ignition timing in FIG. The range changes to B when deposit is present.
That is, as shown in FIG. 5, from the set point a of the injection timing and ignition timing when there is no deposit accumulation (A), to the point b1 where only the injection timing is advanced when deposit deposit is present (B), or It is necessary to move to point b2 where only the ignition timing is retarded, or to point b3 where both are advanced and retarded, respectively.
[0026]
Therefore, the control unit 12 corrects and controls the fuel injection timing and / or the ignition timing according to the flowchart described below.
FIG. 6 is a flowchart of the correction control, which is executed every predetermined time. This flow corresponds to correction means.
In S1, it is determined whether or not the operation is in stratified combustion. If YES, the process proceeds to S2. In the case of NO, since the fuel injection control and ignition timing control during normal homogeneous combustion are separately performed, this flow ends.
[0027]
In S2, a deposit accumulation amount counter C calculated and stored according to a flow chart (for example, FIG. 7) of deposit deposit amount counter C described later is read. The counting method of the deposit accumulation amount counter C will be described later, but corresponds to an estimated value of the deposit accumulation amount at the tip of the injector 7.
In S3, the injection timing IT without deposit accumulation is calculated using a fuel injection timing calculation method during normal stratified combustion.
[0028]
In S4, the ignition timing ADV when there is no deposit is calculated using a normal ignition timing calculation method during stratified combustion.
In S5 (or S5 ′ or S5 ″), the fuel injection timing IT and / or the ignition timing ADV are corrected in accordance with the value of the deposition amount counter C.
That is, when correcting only the injection timing, in S5,
IT = IT + K1 × C (1)
As a result, the product of the deposition amount counter C and a predetermined coefficient K1 is added to the injection timing (advance value from the compression top dead center) IT. Correct the advance angle.
[0029]
When only the ignition timing is corrected, in S5 ′,
ADV = ADV−K2 × C (2)
By subtracting the product of the deposition amount counter C and a predetermined coefficient K2 from the ignition timing (advance value from the compression top dead center) ADV, the injection timing IT is increased as the deposition amount increases. Correct the delay angle.
[0030]
Further, when correcting both the injection timing and the ignition timing, in S5 ″,
IT = IT + K1 × C (1)
ADV = ADV−K2 × C (2)
As the deposit amount increases, the injection timing IT is advanced and the ignition timing ADV is retarded.
[0031]
In S6, fuel injection is performed at the corrected injection timing IT. In S7, ignition is performed at the corrected ignition timing ADV, and this flow is finished.
Next, an estimation of the deposit accumulation amount on the tip of the injector 7, that is, a method for calculating the deposit accumulation amount counter C corresponding to the estimated deposit accumulation amount will be described.
[0032]
FIG. 7 is a flowchart of the first embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow corresponds to the accumulation amount estimation means.
In S11, it is determined whether or not the initialization condition is satisfied. Here, the initialization condition is when the engine is started for the first time (when the engine is new). At this time, the process proceeds to S12 and the deposit accumulation counter C is cleared (C = 0).
[0033]
In S13, the injector tip temperature T detected by the injector tip temperature sensor 16 is read.
In S14, the deposition amount counter C is incremented by the following equation.
C = C + K3 × (T0−T)
That is, as the injector tip temperature T is lower (than the reference temperature T0), the deposit adhesion amount increases. Therefore, the product of (T0-T) and a predetermined coefficient K3 is added to the deposition amount counter C. Estimate the deposit amount.
[0034]
In the present embodiment, the accumulated amount estimated value (depot accumulated amount counter C) is obtained by cumulatively increasing with the passage of time of engine operation, and the degree of increase is determined by the engine operating state, particularly the tip temperature of the injector 7. The estimation accuracy is improved by changing it accordingly.
FIG. 8 is a flowchart of the second embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow also corresponds to the accumulation amount estimation means.
[0035]
S11 and S12 are the same as the flow of FIG.
In S15, the engine water temperature Tw detected by the water temperature sensor 15 is read.
In S16, the deposition amount counter C is incremented by the following equation.
C = C + K4 × (Tw0−Tw)
That is, as the engine water temperature Tw is lower (than the reference temperature Tw0), the injector tip temperature is lower and the deposit adhesion amount increases. Therefore, the product of (Tw0-Tw) and a predetermined coefficient K4 is calculated as the deposit amount counter C. Is added to estimate the deposit amount.
[0036]
In this embodiment, the deposit amount is estimated using the engine water temperature Tw, which is a parameter related to the injector tip temperature, and it is not necessary to provide a special injector tip temperature sensor.
FIG. 9 is a flowchart of the third embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow also corresponds to the accumulation amount estimation means.
[0037]
S11 and S12 are the same as the flow of FIG.
In S17, the intake air amount Qa detected by the air flow meter 14 is read as the engine load.
In S18, the deposition amount counter C is incremented by the following equation.
C = C + K5 × (Qa0−Qa)
That is, as the intake air amount Qa corresponding to the engine load is lower (than the reference intake air amount Qa0), the injector tip temperature becomes lower and the deposit adhesion amount increases, so that (Qa0−Qa) and a predetermined coefficient K5 By adding the product to the deposit accumulation counter C, the deposit accumulation amount is estimated.
[0038]
In the present embodiment, the deposit, which is a parameter related to the injector tip temperature, specifically, the intake air amount Qa is estimated, and there is no need to provide a special injector tip temperature sensor.
FIG. 10 is a flowchart of the fourth embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow also corresponds to the accumulation amount estimation means.
[0039]
S11 and S12 are the same as the flow of FIG.
In S19, it is determined whether or not the fuel is cut during deceleration operation.
If the fuel is not being cut, this flow is terminated as it is. If the fuel is being cut, the process proceeds to S20.
In S20, the deposition amount counter C is incremented by the following equation.
[0040]
C = C + ΔC
That is, during the fuel cut, the injector tip temperature becomes low and deposits are likely to accumulate. Therefore, the deposit accumulation amount is estimated by adding a predetermined increment ΔC to the deposit accumulation amount counter C.
In the present embodiment, when the fuel cut is not being performed, the increment of the deposition amount counter C is set to 0. However, an increment smaller than the increment ΔC during the fuel cut may be added.
[0041]
FIG. 11 is a flowchart of the fifth embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow also corresponds to the accumulation amount estimation means.
S11 and S12 are the same as the flow of FIG.
In S21, an increment CC of the deposition amount counter is obtained from the current injection timing with reference to the table of FIG.
[0042]
In S22, the deposition amount counter C is incremented by the following equation.
C = C + CC
That is, the deposit CC is estimated by adding the increment CC corresponding to the injection timing to the deposit deposit counter C.
Here, as can be seen from FIG. 12, as the injection timing is closer to the intake TDC, the increment CC of the deposition amount counter is increased. This is because when the injection timing is close to the intake TDC, the spray collides with the piston and the collided spray rebounds in the direction of the injector, so that fuel adheres to the injector tip and the deposit accumulation amount increases.
[0043]
Further, the closer to the intake valve full lift, the larger the increment CC of the deposition amount counter. This is because if the injection is performed when the intake valve lift is large, the spray collides with the intake valve, and the collided spray rebounds in the direction of the injector, so that fuel adheres to the injector tip and the deposit accumulation amount increases.
Further, the closer to the compression TDC, the larger the increment CC of the deposition amount counter. This is because when the injection timing is close to the compression TDC, the in-cylinder pressure becomes high and the spray penetration force becomes weak, so that the fuel spray density near the tip of the injector becomes high and the deposit accumulation amount increases.
[0044]
FIG. 13 is a flowchart of the sixth embodiment for calculating the deposition amount counter C, which is executed every predetermined time. This flow also corresponds to the accumulation amount estimation means.
S11 and S12 are the same as the flow of FIG.
In S23, the signal of the fuel property sensor 17 is read to determine the fuel vaporization characteristic value V. The vaporization characteristic value V is such that the larger the value is, the worse the vaporization is, and it is equal to the degree of heavyness.
[0045]
In S24, the deposition amount counter C is counted up by the following equation.
C = C + K6 × V
That is, gasoline fuel is composed of hydrocarbons of various compositions, and the deposit amount varies depending on the composition, and in particular, the heavier the fuel properties (the worse the vaporization characteristics), the greater the deposit amount. The deposit accumulation amount is estimated by adding the product of the vaporization characteristic value V and a predetermined coefficient K6 to the deposit accumulation amount counter C.
[0046]
FIG. 14 is a flowchart of the seventh embodiment for calculating the deposition amount counter C, which is executed in a timely manner. This flow also corresponds to the accumulation amount estimation means.
In S25, the mileage D calculated and integrated from the vehicle speed sensor signal in the odometer 18 is read.
In S26, the deposition amount counter C is calculated by the following equation.
[0047]
C = K7 × D
That is, as the travel distance D increases, the deposit accumulation amount increases. Therefore, the deposit accumulation amount is estimated in proportion to the travel distance D by multiplying the travel distance D by a predetermined coefficient K7.
It should be noted that when the deposit is deposited in a certain amount, that is, when it is deposited to some extent, its surface temperature becomes high and burns. Therefore, it is possible to cope with the saturation by providing an upper limiter for the estimated amount of accumulation by the accumulation amount estimating means or the correction value by the correcting means corresponding thereto.
[0048]
Specifically, the flow of FIG. 15 is executed immediately after the deposit deposition amount counter calculation flow shown in FIGS.
In S31 of the flow of FIG. 15, it is determined whether or not the deposition amount counter C has exceeded a predetermined upper limit value Cmax. If exceeded, the deposition amount counter C is regulated to the upper limit value Cmax in S32.
[0049]
In addition to this restriction, in S5 or S5 ′ or S5 ″ of the flow of FIG. 6, the correction amount to the advance side of the injection timing (K1 × C) and the correction amount to the retard side of the ignition timing (K2 × A similar effect can be obtained by providing an upper limiter for C).
[Brief description of the drawings]
FIG. 1 is a system diagram of an engine showing an embodiment of the present invention. FIG. 2 is an explanatory diagram of compression stroke injection during stratified combustion. FIG. 3 is an explanatory diagram of injection timing during homogeneous combustion and stratified combustion. ] Illustration of injector fuel spray [Fig. 5] Diagram showing combination of injection timing and ignition timing capable of stratified combustion [Fig. 6] Flow chart of correction control [Fig. 7] Flow chart of depot accumulation amount counter calculation (1) [Fig. 8] Flow chart of deposit deposition amount counter calculation (2) [FIG. 9] Flow chart of deposition deposit amount counter calculation (3) [FIG. 10] Flow chart of deposition deposit amount counter calculation (4) [FIG. Flowchart of 5) [Fig. 12] Fig. 13 is a diagram showing a table for calculating the deposit accumulation amount. [Fig. Flow chart of the flow chart Figure 15 the upper limiter of the counter calculation (7) Description of symbols]
1 Engine 2 Piston 3 Combustion chamber 7 Injector 11 Spark plug 12 Control unit 13 Crank angle sensor 14 Air flow meter 15 Water temperature sensor 16 Injector tip temperature sensor 17 Fuel property sensor 18 Odometer

Claims (9)

In a direct-injection spark-ignition engine including an injector that directly injects fuel into a cylinder and an ignition plug,
A deposition amount estimating means for estimating the amount of deposits on the injector tip, during stratified charge combustion to the fuel injection in the compression stroke, according to the estimated accumulation amount, and correcting at least one of the fuel injection timing or ignition timing The direct injection spark ignition is characterized in that when the fuel injection timing is corrected, a correction means is provided that corrects the advance angle as the accumulation amount increases, and when the ignition timing is corrected, the correction means corrects the delay angle as the accumulation amount increases. Type engine control device. 2. The control apparatus for a direct injection spark ignition engine according to claim 1, wherein the accumulation amount estimation means obtains an accumulation amount estimated value by cumulatively increasing with the passage of time of engine operation. 3. The direct-injection spark-ignition engine control device according to claim 2, wherein the degree of increase of the accumulation amount estimation value is changed according to an engine operating state. 4. The control apparatus for a direct injection spark ignition engine according to claim 3, wherein the engine operating state that changes the degree of increase in the estimated amount of accumulation is an injector tip temperature or a parameter related thereto. The direct-injection spark-ignition engine control device according to claim 3, wherein the engine operating state that changes the degree of increase in the estimated accumulation amount is the presence or absence of a fuel cut. 4. The direct-injection spark-ignition engine control device according to claim 3, wherein the engine operating state that changes the degree of increase in the estimated accumulation amount is a fuel injection timing. 4. The direct-injection spark-ignition engine control device according to claim 3, wherein the engine operating state that changes the degree of increase in the estimated accumulation amount is a fuel property. 2. The control apparatus for a direct injection spark ignition engine according to claim 1, wherein the accumulation amount estimating means obtains an accumulation amount estimated value in substantially proportion to a travel distance. The direct eruption according to any one of claims 1 to 8, wherein an upper limiter is provided for the accumulation amount estimated value by the accumulation amount estimation means or the correction value by the correction means corresponding thereto. Control device for a flower ignition engine.

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