JP3823510B2 - In-cylinder direct injection internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder direct injection internal combustion engine, and more particularly, to control of fuel injection timing in accordance with valve timing of intake and exhaust valves.
[0002]
[Prior art]
Conventionally, as disclosed in JP-A-8-35429, a spark ignition type internal combustion engine, fuel is directly injected into a cylinder in the second half of a compression stroke from a fuel injection valve provided in a combustion chamber, An in-cylinder direct injection internal combustion engine has been proposed in which a combustible air-fuel mixture is collected in the vicinity of a spark plug and stratified combustion is performed so that stable combustion can be realized while being an extremely lean air-fuel mixture as a whole. By injecting fuel in the latter half of the compression stroke, it prevents diffusion of the injected fuel, maintains a relatively rich mixture layer near the spark plug during ignition, and enables stable ignition combustion and flame propagation. Overall, it is possible to operate with an ultra-lean air-fuel mixture, and the fuel consumption and exhaust composition are greatly improved.
[0003]
As described in JP-A-2-245406, the valve timing of the internal combustion engine, that is, the opening / closing timing of the intake / exhaust valve is changed depending on the operating conditions, and at the same time, by adjusting the ignition timing and the air-fuel ratio, for example, low load By making the valve overlap relatively large in the region, etc., the exhaust amount flowing back from the exhaust system to the intake system is increased to increase the internal exhaust gas recirculation (EGR) rate, thereby reducing the NOx emission amount, etc. Are known.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional direct injection type internal combustion engine, the fuel injection timing at the time of stratified combustion is basically the timing required to form and maintain a combustible mixture layer necessary for stratified combustion. It is fixed to.
[0005]
For this reason, when variable control of the intake / exhaust valve timing is applied, the stability of combustion is not always optimally maintained, and it is difficult to maximize the exhaust performance and fuel consumption characteristics of the engine. It was.
[0006]
The present invention solves such a technical problem, and further reduces NOx and HC while maintaining combustion stability by changing the fuel injection timing in accordance with the change in valve timing during stratified combustion. It aims to plan.
[0007]
[Means for Solving the Problems]
Accordingly, a first invention is a fuel injector for directly injecting fuel into a combustion chamber, a fuel injection timing control means for setting the fuel injection from the fuel injector at the second half of the compression stroke at the time of stratified combustion, and an injected fuel In a direct injection type internal combustion engine equipped with an ignition plug for igniting, a valve timing variable control means for variably controlling the valve timing of at least one of an intake valve and an exhaust valve, and a fuel injection timing during stratified combustion And a fuel injection timing correction unit that corrects the fuel injection timing according to a change in timing. The fuel injection timing correction unit corrects the fuel injection timing to the retard side as the valve overlap amount increases due to the change in valve timing.
[0009]
In a second aspect based on the first aspect, the fuel injection timing correction means corrects the fuel injection timing while detecting a change in actual valve timing.
[0010]
According to a third invention, in the first and second inventions, the fuel injection timing correction means includes a first correction amount based on the valve overlap amount, and a second correction according to the engine speed and the load. And the injection timing is corrected to the retard side based on these.
[0011]
In a fourth aspect based on the first aspect, the fuel injection timing correction means corrects the fuel injection timing to the retard side in accordance with the combustion stability that fluctuates due to a change in valve timing.
[0012]
In a fifth aspect based on the fourth aspect, the fuel injection timing correction means corrects the fuel injection timing to the retard side as the rotational speed fluctuation as the combustion stability increases.
[0013]
According to a sixth aspect of the present invention, there is provided a fuel injector for directly injecting fuel into a combustion chamber, a fuel injection timing control means for setting the fuel injection from the fuel injector at the second half of the compression stroke at the time of stratified combustion, In a direct injection type internal combustion engine equipped with an ignition plug that ignites and an exhaust gas recirculation device that recirculates part of the exhaust gas into the intake air, the valve timing of at least one of the intake valve and the exhaust valve is variably controlled during stratified combustion And a fuel injection timing correcting means for correcting the fuel injection timing at the time of stratified combustion according to the change of the valve timing. The fuel injection timing correcting means is configured to change the valve timing by changing the valve timing. while correcting retarded fuel injection timing as the amount of overlap increases, and means for measuring the degree of combustion stability, combustion stability of stratified combustion The Based on the result of comparison with the set value of the stability limit due to the limit of stability and external exhaust gas recirculation stability combustion by the internal exhaust gas recirculation comprises means for determining an abnormality of the variable valve timing control means or the exhaust gas recirculation device.
[0014]
In a seventh aspect based on the sixth aspect, the abnormality determining means sets the valve overlap amount and the injection timing correction amount to minimum values, respectively, when the abnormality of the valve timing variable control means is determined.
[0015]
In the first invention, when the valve timing is changed during stratified combustion, the internal exhaust gas recirculation rate fluctuates accordingly. As the internal exhaust gas recirculation rate increases, NOx can be reduced by that amount. However, the temperature of the injected fuel increases due to the high-temperature recirculated exhaust gas, and the fuel tends to diffuse, so stratified combustion tends to become unstable. In such a case, fuel diffusion is suppressed by delaying the fuel injection timing, thereby shortening the period until ignition after fuel injection. As a result, a combustible air-fuel mixture layer is formed and maintained in the vicinity of the spark plug at the time of ignition, and stable stratified combustion can be maintained. In this way, combustion stability can be ensured while further reducing NOx and HC. it can.
[0016]
In the second aspect of the invention, the fuel injection timing is corrected corresponding to the actual valve timing, so that the control that accurately reflects the internal exhaust gas return rate can be performed.
[0017]
In the third aspect of the invention, the internal exhaust gas recirculation rate changes when the rotational speed and load at that time fluctuate even with the same valve overlap, but the fuel injection timing is corrected even in response to this rotational speed and load fluctuation. Therefore, control with high combustion stability can be performed.
[0018]
In the fourth and fifth inventions, the fuel injection timing is controlled while measuring the actual combustion stability by detecting the rotational speed fluctuation, etc., so that the control with high combustion stability is performed while the valve timing is open control. Is possible.
[0019]
In the sixth invention, when an abnormality occurs in the internal exhaust gas recirculation and the external exhaust gas recirculation and the exhaust gas is recirculated excessively, the combustion stability is significantly impaired. However, since the recirculation exhaust gas temperature is higher and the diffusion of fuel is faster, the stratified combustion is likely to be impaired, and the combustion stability is deteriorated. Therefore, by making a difference in the set value of the stability limit of combustion, it is possible to immediately determine which cause caused the abnormality.
[0020]
In the seventh invention, when an abnormality occurs in the control of the valve timing, the overlap amount is corrected so as to be minimized, so that the fail-safe function can be exhibited and the instability of combustion can be prevented.
[0021]
Embodiment
The best mode for carrying out the present invention will be described below with reference to the drawings.
[0022]
In FIG. 1, 1 is a cylinder block, 2 is a cylinder head, and 3 is a piston. Fuel is directly injected from a fuel injector 5 into a combustion chamber 11 defined by these. An ignition plug 4 ignites and burns the mixture with the injected fuel near the compression top dead center.
[0023]
6 is an intake passage, 7 is an exhaust passage, 8 is an intake throttle valve provided in the intake passage 6, 9 is an intake valve, 10 is an exhaust valve, and 23 is taking in part of the exhaust to reduce NOx An exhaust gas recirculation passage 24 and a control valve 24 for adjusting the exhaust gas recirculation amount constitute an external exhaust gas recirculation device (external EGR device).
[0024]
A well-known variable valve timing control mechanism (not shown) is provided so that at least one of the valve timings of the intake valve 8 and the exhaust valve 9 is variably changed according to operating conditions. This variable control mechanism, for example, relatively advances or retards the rotation angle of the camshaft that drives the intake valve 8, and if the valve closing timing of the intake valve 8 is delayed by delaying, the exhaust valve 9. And the valve overlap (period) increases.
[0025]
A control device 20 for the fuel injector 5 controls the fuel injection timing and the injection period in accordance with the operating conditions. Therefore, the control device 20 includes an air flow meter 12 that detects the intake air amount, a crank angle sensor 13 that detects the engine crank angle, a water temperature sensor 14 that detects the cooling water temperature, and an exhaust air-fuel ratio sensor that detects the oxygen concentration in the exhaust gas. 15. Signals representative of driving conditions are input from a throttle opening sensor 16 that detects the opening of the throttle valve, a vehicle speed sensor 17 that detects the vehicle speed, a fuel pressure sensor 18 that detects the fuel injection pressure, and the like. A fuel pressure control device 21 controls the fuel injection pressure (common rail pressure). The actual fuel injection amount is determined from the fuel pressure and the fuel injection period.
[0026]
As shown in FIG. 2, the fuel injector 5 determines the injection timing so that fuel injection is performed in the latter half of the compression stroke in principle during lean stratified combustion executed in a partial load region of the engine load. , Prevents the diffusion of fuel during ignition, forms a combustible mixture layer near the spark plug, and realizes stable stratified combustion while maintaining an extremely lean mixture as a whole. During homogeneous premixed (normal) combustion at the stoichiometric air-fuel ratio, etc., fuel injection is performed during the intake stroke to form a homogeneously mixed mixture in the combustion chamber during ignition.
[0027]
In the present invention, as shown in FIG. 3, during stratified combustion, the valve timing is changed so that the valve overlap is larger than during normal combustion, and the internal exhaust gas recirculation (internal EGR) rate is set separately from the external EGR. In order to increase and further reduce the generation of NOx and prevent the instability of combustion due to this, the control device 20 delays the fuel injection timing during stratified combustion as the valve overlap increases. Correction control to the corner side.
[0028]
The contents of this control will be described with reference to the flowchart of FIG.
[0029]
First, in step S1, it is determined whether or not the current operating condition is stratified combustion. When stratified operation is performed at the time of partial load or the like, the process proceeds to step S2 to increase the engine speed N and the fuel injection pulse width (load) Tp. Based on this, the basic fuel injection timing IT and ignition timing (advance value) ADV are set. As shown in FIG. 5, the basic fuel injection timing IT is set so as to be on the advance side (front side of the compression stroke) as the rotational speed and load increase.
[0030]
In step S3, the valve timing (valve overlap amount of the intake / exhaust valve) ΔV is set based on the rotational speed N and the load Tp. As this valve overlap increases, the amount of exhaust flowing back to the intake system increases, and the amount of internal EGR (residual exhaust amount) increases, thereby reducing the amount of NOx generated accordingly.
[0031]
The variable valve timing control mechanism controls the operation timing of the intake / exhaust valves so that this valve timing ΔV is obtained, and in step S4, the actual valve timing ΔV ′ that changes in accordance with this is detected.
[0032]
In step S5, the actual valve timing ΔV ′ is replaced as the target valve timing ΔV, and the correction amount ΔIT of the fuel injection timing is calculated from the table set to the characteristics shown in FIG. 6 based on the valve timing ΔV.
[0033]
In general, when the valve overlap amount is large and the internal EGR amount increases, fuel vaporization progresses due to high-temperature exhaust, and at the same time, the fuel diffuses and the air-fuel mixture layer near the spark plug near the compression top dead center becomes much less diluted. This tends to impair the stability of ignition and subsequent flame propagation. On the other hand, if the fuel injection timing is retarded, the period until ignition is shortened by that amount, diffusion of fuel from injection to ignition is suppressed, and maintenance of the combustible air-fuel mixture layer is facilitated. Combustion is stabilized. Therefore, the correction amount ΔIT is set so that the retardation amount increases as the valve overlap amount increases.
[0034]
Since the correction amount ΔIT is calculated based on the detected value of the actual valve timing, the fuel injection timing can be made to correspond accurately to the internal EGR amount.
[0035]
In step S7, the correction amount ΔIT is added to the above-described fuel injection timing IT as a fuel injection timing, and is set as fuel injection timing IT = IT + ΔIT (corrected to the retarded angle side), thereby injecting from the fuel injector. Take control.
[0036]
Next, the overall operation will be described.
[0037]
Stratified combustion is performed with an ultra-lean air-fuel mixture, such as during partial load operation of an engine. At this time, fuel is injected from the fuel injector 5 in the second half of the compression stroke, and the injected fuel stays inside the rising hemispherical space (ball) 3a of the piston top surface, thereby forming and maintaining a combustible mixture layer. When this is ignited by the spark plug 4, the flame propagates to the layered mixture, and even if the mixture is extremely lean as a whole, combustion is stably performed.
[0038]
In addition to external exhaust gas recirculation from the exhaust gas recirculation passage 23 during this stratified combustion, if the intake / exhaust valve timing is changed and the valve overlap amount is increased, the internal EGR amount (residual exhaust gas amount) in the cylinder is accordingly increased. As the internal EGR amount increases, the NOx generation amount relatively decreases. However, the diffusion of fuel proceeds simultaneously with the vaporization of the fuel injected in the compression stroke due to the increase in the high-temperature internal recirculation exhaust. If the fuel diffuses widely in the combustion chamber, the concentration of the air-fuel mixture in the vicinity of the spark plug 4 at the time of ignition becomes thin, the combustible air-fuel mixture cannot be maintained, and the stability of ignition is impaired.
[0039]
However, when the valve overlap amount is increased, the fuel injection timing is corrected to the retard side accordingly, that is, the injection timing is shifted further in the latter half of the compression stroke. For this reason, even if the tendency of the injected fuel to diffuse due to high-temperature exhaust increases, the period from injection to ignition is shortened, and it becomes possible to reliably form and maintain a combustible mixture layer in the vicinity of the spark plug 4 at the time of ignition. .
[0040]
In this way, when the valve overlap is increased, as shown in FIG. 3, the fuel injection timing is delayed in accordance with this, thereby maintaining the stratification of the air-fuel mixture and promoting the vaporization of the injected fuel. Thus, good stratified combustion can be maintained, and NOx can be further reduced by increasing the amount of internal EGR. In this case, as can be seen from FIG. 3, the combustion stability deteriorates even if the injection timing is advanced or delayed from the optimal fuel injection timing for a certain valve overlap amount. It can be understood that there is an optimum value of the fuel injection timing in each.
[0041]
Note that during normal combustion with the stoichiometric air-fuel ratio, the valve timing is controlled to an optimal timing for normal combustion, and the fuel injection timing is adjusted to an optimal timing according to this timing.
[0042]
Next, another embodiment will be described with reference to FIG.
[0043]
Even if the valve timing of the intake and exhaust valves is constant, the internal EGR amount varies if the engine operating conditions are different. For example, as shown in FIG. 8, the amount of internal EGR increases as the load decreases and the rotational speed decreases.
[0044]
Therefore, in this embodiment, the fuel injection timing is corrected in accordance with the actual internal EGR amount.
[0045]
FIG. 7 shows a flowchart of the control operation of the fuel injection timing, which is the same as FIG. 4 until the calculation of ΔIT from the valve timing ΔV in step S6. Thereafter, in step S7, the rotational speed N and the load Tp are increased. Based on the above, a second correction amount ΔIT1 is calculated from a table as shown in FIG. 8, and the fuel injection timing is calculated in step S8, and the first correction amount ΔIT based on the valve timing with respect to the basic injection timing IT. And the second correction amount ΔIT1 corresponding to the operation state is obtained.
[0046]
In this way, even if the valve timing is the same, the fuel injection timing is corrected to the retard side as the load and the rotational speed become smaller, and the fuel injection timing is controlled to the injection timing commensurate with the actual increase in the internal EGR amount. Sex can be reliably maintained.
[0047]
Next, still another embodiment of FIG. 9 will be described.
[0048]
Since there is a certain correlation between the valve timing conversion amount, that is, the valve overlap amount and the combustion stability, the correction amount of the fuel injection timing is calculated in relation to the combustion stability.
[0049]
Therefore, in step S4, ΔV1 corresponding to the actual valve timing is calculated based on the combustion stability ΔN. In this case, ΔN is obtained as a fluctuation amount per unit time of the rotational speed N as the engine rotational speed fluctuation, and the valve timing ΔV1 is calculated from the table shown in FIG. 10 based on the rotational speed fluctuation. If the external EGR rate is made constant, the greater the valve overlap amount (internal EGR amount), the worse the combustion stability and the greater the rotational speed fluctuation.
[0050]
In step S5, ΔV1 is replaced with the actual valve timing ΔV, and based on this, a correction amount ΔIT of the fuel injection timing is obtained in the same manner as described above (step S6). In step S7, the fuel injection timing is set as IT = IT + ΔIT. calculate.
[0051]
In this way, even if the actual valve timing reflecting the internal EGR amount is not detected, the substantial internal EGR amount can be accurately grasped from the rotational speed fluctuation obtained from the differential value of the crank angle sensor output. Correspondingly, the retard correction of the appropriate fuel injection timing can be performed.
[0052]
Still another embodiment will be described with reference to FIG.
[0053]
Here, abnormality in valve timing (internal EGR) and abnormality in external EGR are determined from the combustion stability, that is, the magnitude of the rotational speed fluctuation, and control of the fuel injection timing is not confused when these abnormalities occur. is doing.
[0054]
For this reason, when the combustion stability ΔN is read in step S4, it is compared with a first predetermined value ΔN1 indicating the stability limit in step S5.
[0055]
As shown in FIG. 10, the first predetermined value ΔN1 is a limit value of the combustion stability when the valve overlap amount is increased when the external EGR rate is made constant, and this ΔN1 If ΔN is larger than the value, it is determined that the stability limit has been exceeded. Then, the process proceeds to step S6, where the valve timing ΔV and the injection timing correction amount ΔIT are set to zero, that is, the internal EGR rate is returned to the minimum value, and it is determined in step S7 that the valve timing is abnormal.
[0056]
On the other hand, when it is determined in step S5 that the combustion stability ΔN is equal to or less than ΔN1, the magnitude is compared with the second predetermined value ΔN2 in step S6. As shown in FIG. 12, the second predetermined value ΔN2 is the combustion stability when the valve timing ΔV is constant (the internal EGR amount is constant for the same load and rotation speed) and the external EGR rate is increased. When ΔN is larger than ΔN2, it is determined that the stability limit has been exceeded, the process proceeds to step S9, and it is determined that the external EGR is excessively performed.
[0057]
As shown in FIG. 13, ΔN1 is larger than ΔN2 as the stability limit value. With the same amount of internal EGR and external EGR, the internal EGR has a higher in-cylinder temperature, which makes it easier for the injected fuel to diffuse, and the combustion stability is relatively deteriorated. Therefore, the stability at the same EGR rate is maintained. As the limit value, the limit value due to internal EGR is increased.
[0058]
When the combustion stability is equal to or less than ΔN2, both the internal EGR and the external EGR are considered to be in the normal range, and the process proceeds to step S10, and the valve timing ΔV1 is calculated based on ΔN as in the embodiment of FIG. After replacing this with ΔV, a correction amount ΔIT is calculated according to ΔV, and the fuel injection timing is obtained by adding the correction amount ΔIT to the injection timing IT (steps S10 to S13).
[0059]
When stratified combustion is normally performed, the external EGR rate is determined according to the operating conditions, and separately from this, the internal EGR rate, that is, the valve overlap amount is controlled, and NOx is within a range that does not impair the combustion stability. However, if an abnormality such as a failure occurs in the external EGR device or the variable valve timing control mechanism and EGR is performed excessively, combustion becomes extremely unstable.
[0060]
However, even in such a case, the combustion stability (rotational speed fluctuation) ΔN is judged, and if the combustion stability is worse than the first limit value ΔN1, at least the variable control mechanism of the valve timing has failed. It is determined that an abnormality such as the above has occurred (however, the failure of the external EGR device is also included at the same time).
[0061]
On the other hand, when it is within the first limit value, it is determined that the variable valve timing control mechanism is functioning normally, and in order to determine whether the external EGR device is normal, Comparison with the limit value ΔN2 is performed. When the combustion stability is worse than the second limit value, it can be determined that the external EGR device is in an abnormal state such as a failure, and by displaying these determination results, etc. Can encourage appropriate treatment.
[0062]
Also, when the combustion stability is worse than the first limit value, the valve timing conversion amount is set to zero and the injection timing correction amount is set to zero to reduce the internal EGR, so that the fail-safe function can be exhibited. If it is less than or equal to the first limit value but worse than the second limit value, the failure of the external EGR device is judged, but the combustion stability has not reached the first limit value, so the injection is performed as it is. Continue timing correction.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an overall configuration of a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing fuel injection timing during stratified combustion.
FIG. 3 is an explanatory diagram showing the relationship between the valve timing (valve overlap amount) during stratified combustion and the combustion stability, NOx generation amount, etc. when the fuel injection timing is changed.
FIG. 4 is a flowchart showing the control content of the first embodiment.
FIG. 5 is a characteristic diagram showing the fuel injection timing based on the rotational speed and the fuel injection pulse width.
FIG. 6 is a characteristic diagram showing the relationship between the valve timing (valve overlap amount) and the fuel injection timing correction amount.
FIG. 7 is a flowchart showing control contents of the second embodiment.
FIG. 8 is a characteristic diagram showing the relationship between changes in internal EGR amount with respect to rotation speed and load fluctuation at the same valve timing.
FIG. 9 is a flowchart showing control contents of the third embodiment;
FIG. 10 is a characteristic diagram showing the relationship between valve timing and combustion stability when the external EGR rate is constant.
FIG. 11 is a flowchart showing control contents of the fourth embodiment;
FIG. 12 is a characteristic diagram showing the relationship between the external EGR rate and the combustion stability when the internal EGR rate is constant.
FIG. 13 is a characteristic diagram showing the relationship between combustion stability and stability limit.
[Explanation of symbols]
3 Piston 4 Spark plug 5 Fuel injector 6 Intake passage 7 Exhaust passage 9 Intake valve 10 Exhaust valve 20 Control device

Claims (7)

A fuel injector for directly injecting fuel into the combustion chamber, fuel injection timing control means for setting the fuel injection from the fuel injector at the second half of the compression stroke at the time of stratified combustion, and an ignition plug for igniting the injected fuel In the in-cylinder direct injection internal combustion engine, the variable valve timing control means for variably controlling the valve timing of at least one of the intake valve and the exhaust valve, and the fuel injection timing at the time of stratified combustion is corrected according to the change of the valve timing In-cylinder direct injection internal combustion engine, wherein the fuel injection timing correction means corrects the fuel injection timing to the retard side as the valve overlap amount increases due to a change in valve timing. organ. The in-cylinder direct injection internal combustion engine according to claim 1 , wherein the fuel injection timing correction means corrects the fuel injection timing while detecting a change in actual valve timing. The fuel injection timing correction means calculates a first correction amount based on the valve overlap amount and a second correction amount according to the engine speed and the load, and retards the injection timing based on these. The in-cylinder direct injection internal combustion engine according to claim 1 or 2 , wherein the correction is made to the side. The in-cylinder direct injection internal combustion engine according to claim 1, wherein the fuel injection timing correction means corrects the fuel injection timing to the retard side in accordance with the combustion stability that fluctuates due to a change in valve timing. The in-cylinder direct injection internal combustion engine according to claim 4 , wherein the fuel injection timing correction means corrects the fuel injection timing to the retard side as the rotational speed variation as the combustion stability increases. A fuel injector for directly injecting fuel into the combustion chamber, a fuel injection timing control means for setting the fuel injection from the fuel injector during the stratified combustion to be in the second half of the compression stroke, an ignition plug for igniting the injected fuel, In a cylinder direct injection internal combustion engine provided with an exhaust gas recirculation device that recirculates a part of exhaust gas into intake air, variable valve timing control means for variably controlling the valve timing of at least one of an intake valve and an exhaust valve during stratified combustion And a fuel injection timing correction means for correcting the fuel injection timing during stratified combustion in accordance with the change in the valve timing. The fuel injection timing correction means increases the amount of valve overlap due to the change in the valve timing. while correcting the injection timing to the retard side, means for measuring the degree of combustion stability, internal exhaust gas recirculation combustion stability during stratified charge combustion A variable valve timing control means or a means for judging an abnormality of the exhaust gas recirculation system based on the result of comparison with each set value of the stability limit of combustion stability and the stability limit due to external exhaust gas recirculation Internal direct injection internal combustion engine. The in-cylinder direct injection internal combustion engine according to claim 6 , wherein the abnormality determining means sets the valve overlap amount and the correction amount of the injection timing to minimum values when determining abnormality of the valve timing variable control means.

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