JP3879568B2 - In-cylinder injection spark ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder injection spark ignition internal combustion engine in which fuel directly injected into a cylinder is burned using an ignition plug, and more particularly to a technology at the time of cold start.
[0002]
[Prior art]
In recent years, in-cylinder injection type gasoline engines that realize lean combustion have become widespread. The technique described in Japanese Patent Application Laid-Open No. 11-324778 is an example of such a technique, and in order to avoid oil dilution and smoke generation at the time of cold start at the same time, a predetermined crank angle after the exhaust valve is closed. The intake valve is set to open after a lapse of time, and fuel is injected while both valves are closed. Thus, by not overlapping the open periods of the exhaust valve and the intake valve, a part of the high-temperature combustion gas remains in the combustion chamber, and fuel is injected into the combustion chamber to promote fuel atomization. Describes that it is possible to suppress both the generation of smoke and oil dilution by suppressing the adhesion of fuel to the piston crown surface and the cylinder bore wall surface.
[0003]
[Problems to be solved by the invention]
However, since this technique injects fuel at the beginning of the intake stroke at the time of cold start, it forms a homogeneous homogeneous mixture and performs homogeneous combustion, resulting in a reduction in fuel consumption.
[0004]
Accordingly, an object of the present invention is to provide an in-cylinder injection spark ignition internal combustion engine that realizes an improvement in fuel efficiency during cold start.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problem, a cylinder injection spark ignition internal combustion engine according to the present invention is a cylinder injection spark ignition internal combustion engine in which fuel injected into a cylinder is burned using an ignition plug. An exhaust gas recirculation device that guides and circulates in the interior and means for determining intake pipe negative pressure, and during cold start, the intake pipe negative pressure determined by the means for determining intake pipe negative pressure is greater than a predetermined value. If the intake pipe negative pressure determined by the means for determining the intake pipe negative pressure is equal to or less than a predetermined value while supplying the fuel into the cylinder during the compression stroke while operating the exhaust gas recirculation device, The fuel supply to the cylinder is performed .
[0006]
High temperature exhaust gas is reintroduced into the cylinder by an exhaust gas recirculation (EGR) device, and the intake air in the cylinder is heated to promote atomization of the fuel. Thereby, even at the time of cold start, adhesion of fuel to the cylinder inner wall surface can be suppressed, and smoke generation and oil dilution can be suppressed. Furthermore, by introducing exhaust gas, the combustion temperature can be lowered to reduce the amount of NOx generated.
[0007]
A means for determining the intake pipe negative pressure is further provided, and when the determined intake pipe negative pressure is larger than a predetermined value , fuel is supplied into the cylinder during the compression stroke while the exhaust gas recirculation device is operated . On the other hand, when the determined intake pipe negative pressure is less than or equal to a predetermined value, fuel is supplied into the cylinder during the intake stroke. If the intake pipe negative pressure is small, EGR introduction is difficult, so the temperature in the combustion chamber is low, fuel atomization is hindered, fuel adheres to the cylinder wall, and stable stratified combustion may not be possible. because there is, it suppresses the EGR introduction in such a case, because it is preferable to determine that is impossible compression process injection.
[0008]
The exhaust gas recirculation device is preferably a variable valve mechanism that adjusts the valve overlap amount between the intake valve and the exhaust valve. When the valve overlap is increased, it is possible to promote the backflow of the exhaust gas in the exhaust pipe into the cylinder.
[0009]
At the time of cold start, it is preferable to increase the variable speed of the valve overlap more than other cases. In other cases, that is, when the intake stroke injection is performed, if the EGR amount is increased at a stretch, the EGR gas may be unevenly distributed, so that a homogeneous mixture cannot be formed and combustion instability may occur. There is. On the other hand, since it is sufficient to form a homogeneous air-fuel mixture only in the vicinity of the spark plug during the compression stroke injection, the valve overlap amount can be increased at a stretch, and stable combustion can be performed even if the EGR gas is unevenly distributed. It is possible to do so.
[0010]
This variable valve mechanism may be a mechanism that changes the lift amount of the other when either the intake valve or the exhaust valve is open. Such a lift amount change can be made by using, for example, a three-dimensional cam, and the EGR introduction amount can be controlled without changing the basic timing of intake and exhaust.
[0011]
At the time of cold start, the ignition timing by the spark plug may be further delayed after reaching the top dead center of the piston. By delaying the ignition timing, it is possible to increase the secondary combustion amount and raise the exhaust temperature, improve the warm-up property of the catalyst, and suppress the deterioration of the emission.
[0012]
As the ignition timing delay amount increases, it is preferable to control the operation of the exhaust gas recirculation device so that the amount of recirculated exhaust gas increases. If the ignition timing is delayed, the inside of the cylinder is cooled by the fuel, the amount of adhesion to the wall surface or the like increases, and combustion may become unstable. Therefore, by increasing the EGR amount to increase the in-cylinder temperature and promoting the atomization of fuel, the combustion is stabilized and the generation of black smoke and the like is suppressed.
[0013]
Furthermore, in an area where the ignition timing delay amount is large and combustion is expected to become unstable, the operation of the exhaust gas recirculation device is controlled so that the amount of recirculated exhaust gas decreases as the ignition timing delay amount increases. Is preferred. If the ignition timing delay amount is further increased, the combustion time may be insufficient and the combustion may become unstable. In this case, by suppressing the amount of EGR, the concentration of fuel is enhanced, the combustion time is secured, and the combustion is stabilized.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.
[0015]
FIG. 1 is a schematic diagram showing a direct injection spark ignition internal combustion engine according to the present invention. The internal combustion engine 1 is a gasoline engine of a type in which gasoline as fuel is directly injected into a combustion chamber 13 by a high-pressure injector 43 and is ignited and burned by a spark plug 17.
[0016]
A piston head 11 is disposed in the cylinder 10 of the engine so as to be reciprocally movable in the vertical direction in the figure. The piston head 11 is connected to a crankshaft (not shown) by a connecting rod 12 to convert the reciprocating motion into a rotational motion. To do. A cavity 11A is formed in the upper part (crown surface) of the piston head 11. A space between the crown surface of the piston head 11 and the cylinder head 14 forms a combustion chamber 13.
[0017]
An injector 43, an intake valve 23, an exhaust valve 24, and a spark plug 17 are disposed at a portion of the cylinder head 14 facing the combustion chamber 13. Among these, the injector 43 is disposed in a direction in which fuel can be injected toward the cavity 11 </ b> A of the piston head 11. In addition, the spark plug 17 is disposed between the intake valve 23 and the exhaust valve 24 so as to be positioned in the vicinity of the end opposite to the injector 43 side of the cavity 11A. The intake valve 23 is disposed between the combustion chamber 13 and the intake pipe 15, and the exhaust valve 24 is disposed between the combustion chamber 13 and the exhaust pipe 16. Both valves 23 and 24 are driven by cams 21 and 22, respectively. The variable valve mechanism 2 has a function of changing the opening / closing phase of the intake valve 23 and the exhaust valve 24.
[0018]
The injector 43 is connected to the fuel tank 40 and the fuel pressurized by the pump 41 is sent. A fuel pressure sensor 42 that detects the pressure of the fuel is disposed on the fuel line.
[0019]
The operation of the internal combustion engine 1 is controlled by the engine ECU 3. The engine ECU 3 includes a water temperature sensor 5 for measuring the engine cooling water temperature, a crank angle sensor 6 for measuring the crank angle, and an intake pipe 15 downstream of the throttle 7. Outputs of a negative pressure sensor 8 for detecting a negative pressure, a fuel pressure sensor 42, and the like are input, and the operations of the variable valve mechanism 2, the spark plug 17, and the injector 43 are controlled.
[0020]
FIG. 2 is a diagram for explaining the details of the operation of the variable valve mechanism 2. By adjusting the rotational phase of each of the cams 21 and 22 with respect to the crankshaft, the intake valve 23 and the exhaust valve 24 are opened (valve lift) timing is adjusted, and both the intake valve 23 and the exhaust valve 24 are opened. The length of the valve overlap can be adjusted. Hereinafter, adjusting the valves 23 and 24 to open early (corresponding to shifting the valve lift curve in the drawing to the left) is referred to as adjusting to the advance side, and conversely adjusting to open slowly (see FIG. This is equivalent to shifting the valve lift curve in the middle to the right). The valve overlap amount can be increased by adjusting the intake valve 23 to the advance side or adjusting the exhaust valve 24 to the retard side, or both. That is, it is sufficient that the valve lift timing of at least one of the intake valve 23 and the exhaust valve 24 can be adjusted.
[0021]
Next, the operation at the start of the engine 1 will be described. FIG. 3 is a flowchart showing a first control operation when the engine 1 is started. This control is performed by the engine ECU 3 unless otherwise specified, and is repeatedly executed at a predetermined timing from the start to the stop of the engine 1.
[0022]
In step S1, it is determined whether or not the engine is starting. Here, the start time is a concept including not only the time of starting the engine 1 but also the completion of warm-up of the engine 1 after several minutes from the start. If it is determined in step S1 that the engine is being started, the process proceeds to step S2 where it is determined whether or not the operating condition allows the compression stroke injection. A detailed flowchart of this determination processing is shown in FIG. In step S21, first, the intake pipe negative pressure Pi and the fuel printing pressure Pf are detected by reading the output of the negative pressure sensor 8 and the output of the fuel pressure sensor 42. In the subsequent step S22, the intake pipe negative pressure Pi is compared with the threshold value α. When the intake pipe negative pressure Pi is higher than the threshold value α, the routine proceeds to step S23, where the fuel printing pressure Pf and the threshold value β are compared. When the fuel printing pressure Pf is higher than the threshold value β, the process proceeds to step S24. In step S24, it is assumed that the fuel pressure Pf that can effectively perform the fuel injection in the compression stroke has been reached, and the intake pipe negative pressure Pi that can sufficiently exhibit the EGR effect has been reached. Then, it is determined that the compression stroke injection is possible, and the process is terminated.
[0023]
On the other hand, if it is determined in step S22 that the intake pipe negative pressure Pi is equal to or lower than the threshold value α, the introduction of EGR gas is inhibited, so the temperature in the combustion chamber 13 is low, fuel atomization is inhibited, and the cylinder Since fuel adheres to the 10 wall surface and stable stratified combustion may not be performed, the process proceeds to step S25 and it is determined that the compression stroke injection is impossible. If it is determined in step S23 that the fuel printing pressure Pf is equal to or less than the threshold value β, the fuel printing pressure is insufficient, so that it is not possible to ensure the required amount of fuel injection in the compression stroke. Since misfire has occurred, the process proceeds to step S25, where it is determined that compression stroke injection is not possible.
[0024]
If it is determined that the compression stroke injection is possible as a result of this process, the process proceeds to step S3 in the main process of FIG. 3, and the injection timing is set during the compression stroke. Next, in step S4, the VVT target value is set in a direction in which the overlap amount becomes large, and the process is terminated. As a result, the variable valve mechanism 2 adjusts the phases of the cams 21 and 22 to match the valve lift timings of the intake valve 23 and the exhaust valve 24 with the target values, thereby increasing the valve overlap. 43 performs fuel injection in the compression stroke. By increasing the valve overlap, an internal EGR effect is obtained in which the combustion gas once discharged into the exhaust pipe 16 is again introduced into the combustion chamber 13 in the intake stroke. Thus, by increasing the recirculation amount of the EGR gas, the actual compression ratio is increased, and the temperature in the combustion chamber 12 is increased quickly by the high-temperature combustion gas, thereby promoting fuel atomization and Suppresses fuel from adhering to the inner wall, etc., improves combustion stability by stratification, suppresses black smoke emission, and improves emissions. As a result, stratified combustion can be performed at an air-fuel ratio of about 15 to 16, which is slightly lower than the stoichiometric air-fuel ratio, so that the fuel efficiency and emission at the time of starting are improved.
[0025]
On the other hand, if it is determined in step S2 that the compression stroke injection is not possible, the routine proceeds to step S5, where the injection timing is set during the intake stroke, and in step S6, the VVT target value is set so that the overlap amount becomes small. Set to. In this case, since the compression stroke injection cannot be performed efficiently, the intake stroke injection is performed. However, if the valve overlap amount is increased during the intake stroke injection at the start, the EGR gas is caused to enter the combustion chamber 13. There is a possibility that combustion may become unstable due to uneven distribution and difficulty in mixing uniformly, or due to a slow combustion speed. Therefore, by reducing the valve overlap amount and suppressing the recirculation of the EGR gas, stable combustion is performed and emission deterioration is suppressed.
[0026]
If it is determined in step S1 that the engine is not at the start, the routine proceeds to step S7, where the fuel injection timing and the VVT target value are set according to the load and engine speed. For example, at low rotation and low load, fuel is injected during the compression stroke, stable stratified combustion is performed, and fuel efficiency and emission are improved. At high rotation and high load, high output is secured by performing homogeneous combustion by injecting fuel in the intake stroke to form a homogeneous mixture.
[0027]
When actually adjusting the valve lift timing of the intake valve 23 and the exhaust valve 24 by the variable valve mechanism 2, it is preferable to perform the following control. FIG. 5 is a flowchart showing this adjustment control, and this control is executed following the control process of FIG.
[0028]
First, in step S 1, determines whether the startup. If it is determined that at start, step S 1 determines whether it is set to transition to the compression stroke injection to step S 2. When the compression stroke injection is set, the process proceeds to step S33 to set the valve overlap change speed to a large value, and in step S34, the actual variable valve mechanism 2 is controlled so that this change speed can be obtained. Calculate the amount. In this way, when performing the compression stroke injection, the valve overlap amount is quickly changed to the target value, and the supply amount of the internal EGR is increased, so that the in-cylinder temperature is raised and the fuel is increased. It can promote atomization and stabilize combustion.
[0029]
On the other hand, and not set in the compression stroke injection in the step S 2 If it is determined not to be at starting at step S 1, i.e., if it is determined to be set to the intake stroke injection, to step S35 In step S34, the actual control amount of the variable valve mechanism 2 is calculated so that this change speed is obtained. By doing so, in particular, the sudden change in the valve overlap amount during intake stroke injection is suppressed, and the sudden change in the internal EGR supply amount is suppressed, so that the sudden change in combustion conditions is suppressed and the combustion becomes unstable. To prevent.
[0030]
Subsequently, some of other forms of operation at the start of the engine 1 will be specifically described. First, FIG. 6 is a flowchart showing a second control operation when the engine 1 is started. This control is also performed by the engine ECU 3 unless otherwise specified, and is repeatedly executed at a predetermined timing from the start to the stop of the engine 1.
[0031]
The contents of branch processing from steps S1 to S2 and S7 and branch processing from S2 to S3 and S5 are the same as those in the first control operation shown in FIG. 3, and detailed description thereof is omitted. After the injection timing is set to the compression stroke in step S3, the process proceeds to step S51, and the ignition retard amount is set. This retard amount refers to a map prepared in advance based on the operating state of the engine 1, for example, the engine coolant temperature measured by the water temperature sensor 5 or the negative pressure in the intake pipe 15 measured by the negative pressure sensor 8. You can set in. Thus, a retarding process is performed to delay the ignition timing by the spark plug 17 after reaching the TDC (top dead center) position of the piston head 11 when shifting from the compression stroke to the expansion stroke (hereinafter simply referred to as TDC or later). .
[0032]
In subsequent step S52, a VVT target value is set. This VVT target value is set to an overlap amount that maximizes the intake air amount or the internal EGR amount, for example, according to the engine speed. 7 and 8 are graphs showing how the intake air amount and the internal EGR amount change with respect to the valve overlap amount. As shown in FIG. 7, when the engine speed is the same, there is a valve overlap amount that maximizes the intake air amount. When the valve overlap amount is set to this value, the charging efficiency is maximized. Further, by retarding ignition, the rate of secondary combustion is increased, and the exhaust gas temperature is raised to promote early activation of the catalyst. Thereby, discharge | emission of unburned HC can be suppressed. On the other hand, as for the internal EGR amount, as shown in FIG. 8, when the engine speed is the same, there is a valve overlap amount that maximizes the internal EGR amount. Here, the valve overlap amount at which the intake air amount becomes maximum may coincide with the valve overlap amount at which the internal EGR amount becomes maximum, but usually takes a different value. When the valve overlap amount that maximizes the internal EGR amount is selected, the fuel atomization promotion effect and the early in-cylinder warm-up effect are maximized. Therefore, the black smoke emission reduction effect is maintained while maintaining combustion stability. Can be maximized.
[0033]
On the other hand, when the injection timing is set during the intake stroke at the start in step S5, the process proceeds to step S53, and the ignition timing is set to the advance side. In step S54, the VVT target value is set so that the overlap amount is small, as in step S6 shown in FIG. The control in this case is the same as the first control operation. The same applies to the control other than at the start.
[0034]
In this example, the VVT target value is set to the valve overlap amount that maximizes the intake air amount or the internal EGR amount at the engine speed, but the VVT target value is set based on the ignition retard amount. Also good. In this case, as shown in FIG. 9, the valve overlap amount is maximized when the ignition retardation amount ΔI takes a certain value ΔIth, and the ignition retardation amount increases as the ignition retardation amount ΔI is smaller than this. The valve overlap amount may be set large, and when the ignition delay amount ΔI is larger than this, the valve overlap amount may be set smaller as the ignition delay amount becomes larger. The larger the ignition retard amount, the easier the fuel adheres to the cylinder 10 wall surface. Therefore, in a region where the ignition retardation amount is relatively small, the valve overlap amount increases as the ignition retardation amount increases, thereby increasing the internal EGR amount and increasing the in-cylinder temperature at the time of fuel injection. Atomization is promoted, fuel adhesion to the wall surface of the cylinder 10 is suppressed, and generation of black smoke is suppressed while maintaining combustion stability. On the other hand, the instability of combustion tends to increase as the ignition retardation increases. In the region where the combustion becomes unstable, the combustion stability is improved by reducing the amount of internal EGR.
[0035]
The threshold value ΔIth may be set in advance based on experimental data or the like and held in the engine ECU 3. Further, it may be set during operation based on the combustion state (exhaust air-fuel ratio, rotational speed fluctuation, etc.).
[0036]
In the above description, as shown in FIG. 2, an example has been described in which the valve overlap is changed by moving the valve lift curve to the advance side or the retard side without changing the shape of the valve lift curve. However, for example, as shown in FIG. 10, the cam 22 for opening and closing the exhaust valve 24 has a different cam shape in the axial direction, with only one cam crest 22a in the partial cross section and two in the partial cross section. By adopting a shape having cam peaks 22a and 22b, when the intake valve 23 is open as shown in FIG. 11, the exhaust valve 24 may be opened again. Even when such a valve mechanism is used, the internal EGR can be performed while increasing the valve overlap. The cam 21 for opening and closing the intake valve 23 may have a shape having two cam peaks, and the intake valve 23 may be opened when the exhaust valve 24 is open. In this case, the valve overlap amount can be changed by sliding the cam 21 or 22 in the cam shaft direction, so that the configuration of the variable valve mechanism 2 is simplified and the reliability thereof is further improved. .
[0037]
Of course, a circulation device for returning the burned gas directly from the exhaust pipe 16 to the intake pipe 15 may be provided instead of the valve overlap.
[0038]
【The invention's effect】
As described above, according to the present invention, during cold start, fuel injection is performed in the compression stroke, and EGR gas is introduced to promote fuel atomization and to quickly warm up the cylinder. , Stabilize the combustion and suppress the emission of black smoke and emission.
[0039]
Furthermore, by delaying the ignition timing to transition to TDC, early activation of the catalyst can be realized, warm-up performance can be improved, and deterioration of emissions can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a direct injection spark ignition internal combustion engine according to the present invention.
FIG. 2 is a diagram for explaining the details of the operation of the variable valve mechanism in FIG. 1;
FIG. 3 is a flowchart showing a first control operation when the engine of FIG. 1 is started.
4 is a detailed flowchart of a process for determining whether or not compression stroke injection is possible in FIG. 3;
FIG. 5 is a flowchart of valve lift timing adjustment control executed subsequent to the process of FIG. 3;
6 is a flowchart showing a second control operation when starting the engine of FIG. 1; FIG.
FIG. 7 is a graph showing fluctuations in the intake air amount with respect to the valve overlap amount.
FIG. 8 is a graph showing the variation of the internal EGR amount with respect to the valve overlap amount.
FIG. 9 is a graph showing a valve overlap amount set with respect to an ignition retard amount.
FIG. 10 is a view showing a cam crest shape of an exhaust cam.
11 is a diagram for explaining the details of the operation of the variable valve mechanism using the cam of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Valve lift variable mechanism, 3 ... Engine ECU, 4 ... Injector, 5 ... Water temperature sensor, 6 ... Crank angle sensor, 7 ... Catalyst temperature sensor, 10 ... Cylinder, 11 ... Piston head, 11A ... Cavity , 12 ... Connecting rod, 13 ... Combustion chamber, 14 ... Cylinder head, 15 ... Intake pipe, 16 ... Exhaust pipe, 17 ... Spark plug, 21 ... Intake cam, 22 ... Exhaust cam, 23 ... Intake valve, 24 ... Exhaust valve, .

Claims (7)

In a cylinder injection spark ignition internal combustion engine in which fuel injected into a cylinder is burned using an ignition plug,
An exhaust gas recirculation device that guides and circulates the combustion gas into the cylinder again, and means for determining the intake pipe negative pressure ;
During cold start,
When the intake pipe negative pressure determined by the means for determining the intake pipe negative pressure is larger than a predetermined value, fuel is supplied into the cylinder during the compression stroke while operating the exhaust gas recirculation device.
When the intake pipe negative pressure determined by the means for determining the intake pipe negative pressure is less than or equal to a predetermined value, fuel is supplied into the cylinder during the intake stroke.
An in-cylinder injection spark ignition internal combustion engine. The in-cylinder injection spark ignition internal combustion engine according to claim 1 , wherein the exhaust gas recirculation device is a variable valve mechanism that adjusts a valve overlap amount between the intake valve and the exhaust valve. The in-cylinder spark-ignition internal combustion engine according to claim 2, wherein at the cold start, the variable speed of the valve overlap is increased as compared with other cases. The in-cylinder injection spark ignition internal combustion engine according to claim 2 or 3 , wherein the variable valve mechanism is a mechanism that changes a lift amount of one of the intake valve and the exhaust valve when the other is open. The in-cylinder injection spark ignition internal combustion engine according to any one of claims 1 to 4 , wherein at the time of cold start, the ignition timing by the spark plug is further delayed after reaching the top dead center of the piston. 6. The direct injection spark ignition internal combustion engine according to claim 5, wherein the operation of the exhaust gas recirculation device is controlled so that the amount of recirculated exhaust gas increases as the ignition timing delay amount increases. The operation of the exhaust gas recirculation device is controlled so that the amount of recirculated exhaust gas decreases as the ignition timing delay amount increases in a region where the ignition timing delay amount is large and combustion is expected to become unstable. 6. An in-cylinder injection spark ignition internal combustion engine according to claim 6.

Images