JP3912027B2 - Self-igniting internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-ignition internal combustion engine that performs main combustion by self-igniting and burning at least a part of fuel injected into a cylinder.
[0002]
[Prior art]
In self-ignition combustion, combustion starts simultaneously from multiple points in the main combustion region, so the combustion speed is high, and stable combustion can be achieved even when the air-fuel ratio is lean compared to normal spark ignition combustion. Therefore, the fuel consumption rate can be improved. Further, since the air-fuel ratio is lean and the combustion temperature is lowered, it is possible to significantly reduce NOx in the exhaust gas (see JP-A-7-332141).
[0003]
On the other hand, the NOx trap traps NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and desorbs and purifies NOx trapped when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric (theoretical air-fuel ratio) or rich It is known as an exhaust gas purification device that performs this (see JP-A-6-108824).
In the NOx trap, NOx generated when lean combustion is performed is trapped, and before the NOx trap capability is saturated, additional fuel is injected into the cylinder in the expansion stroke or the exhaust stroke, thereby flowing into the NOx trap. The air-fuel ratio of exhaust gas to be temporarily enriched, thereby desorbing and purifying NOx from the NOx trap (hereinafter, such control is referred to as rich spike control).
[0004]
[Problems to be solved by the invention]
As described above, the self-ignition internal combustion engine has a very low combustion temperature to achieve lean combustion, and NOx in the exhaust gas has a low concentration. However, the NOx emission amount from the engine is not zero, and it is necessary to equip the exhaust passage with a NOx trap in order to realize further reduction of the NOx emission amount.
[0005]
At that time, because of the rich spike control, the in-cylinder residual fuel concentration increases in the next cycle in which additional fuel injection is performed in the expansion stroke, for example. Since the residual fuel is exposed to a high temperature state during the expansion stroke, it is in a very high active state, that is, in a good ignitability state due to a partial oxidation reaction or the like. In general, since self-ignition combustion involves a rapid pressure increase due to multi-point simultaneous ignition, it is very important to control the ignition timing. Therefore, in the next cycle after rich spike control, the ignition timing during main combustion is controlled. If the same parameters are used in comparison with the normal operating conditions, the in-cylinder fuel activation state differs between the two, so the next cycle that performed rich spike control ignited earlier, and pre-ignition There is a problem that the drivability deteriorates due to the above.
[0006]
In view of such a conventional problem, the present invention provides a self-ignition internal combustion engine in the next cycle in which the additional fuel injection is performed when the additional fuel is injected into the cylinder in the expansion stroke or the exhaust stroke. The purpose is to improve the combustion performance.
[0007]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, there is provided a self-ignition internal combustion engine that performs main combustion by self-igniting and burning at least a part of the fuel injected into the cylinder, and expands under predetermined operating conditions. In the case where the additional fuel is injected into the cylinder in the stroke or the exhaust stroke, in the next cycle after the injection of the additional fuel , the residual fuel in the main combustion region, which is the ignition start region at the time of main combustion, and new injection the air-fuel ratio including a fuel, by obtaining the normal operating conditions during the same ignition timing urchin, characterized by leaner than the air-fuel ratio during normal operating conditions.
[0008]
In the invention of claim 2, when fuel injection for main combustion is performed at least once during the intake stroke to the compression stroke, the means for leaning the air-fuel ratio in the main combustion region includes: The fuel injection amount is reduced.
[0009]
According to the third aspect of the present invention, when fuel injection for main combustion is performed at least once during the intake stroke to the compression stroke, the means for leaning the air-fuel ratio in the main combustion region includes: The fuel injection timing is advanced.
In the invention of claim 4, when the fuel injection for the main combustion is performed at least once in the compression stroke, once during the period from the latter exhaust stroke to the injection during the compression stroke, and at least twice in total. The means for leaning the air-fuel ratio in the main combustion region is for reducing the first fuel injection amount.
[0010]
In the fifth aspect of the present invention, when the fuel injection for the main combustion is performed at least twice in total during the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke. The means for leaning the air-fuel ratio in the main combustion region is for advancing the first fuel injection timing.
[0011]
In the sixth aspect of the present invention, when the fuel injection for the main combustion is performed at least once in the compression stroke, once in the period from the late exhaust stroke to the injection during the compression stroke, and at least twice in total. The means for leaning the air-fuel ratio in the main combustion region is for reducing the second fuel injection amount.
[0012]
In the invention of claim 7, when the fuel injection for the main combustion is performed at least once in the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke. The means for leaning the air-fuel ratio in the main combustion region is for advancing the second fuel injection timing.
[0013]
In the invention of claim 8, the exhaust passage is provided with a NOx trap for trapping NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and desorbing and purifying NOx trapped when the air-fuel ratio is stoichiometric or rich, The injection of the additional fuel is performed in order to enrich (stoichiometrically or richly) the air-fuel ratio of the exhaust gas in order to desorb and purify NOx from the NOx trap.
[0014]
【The invention's effect】
According to the invention of claim 1, in the cycle in which the main combustion is performed by self-igniting combustion of a part or all of the fuel, in the next cycle in which the additional fuel injection is performed after the expansion stroke , The air-fuel ratio of the engine is made leaner than the air-fuel ratio under normal operating conditions so as to obtain an ignition timing equivalent to that under normal operating conditions, so it is possible to suppress premature ignition and control the ignition timing appropriately. It becomes.
[0015]
According to the second aspect of the present invention, when the fuel injection for the main combustion is performed at least once, the air-fuel ratio in the main combustion region including the in-cylinder residual fuel and the injected fuel is reduced in order to reduce the fuel injection amount. Can be leaned.
[0016]
According to the invention of claim 3 , when fuel injection for main combustion is performed at least once, in order to advance the fuel injection timing, the in-cylinder residual fuel and the injected fuel are separated by diffusion of the injected fuel. The air-fuel ratio in the main combustion region including it can be made lean.
According to the invention of claim 4 , when performing fuel injection for main combustion at least twice in total, in order to reduce the fuel injection amount for the first time (from the latter stage of the exhaust stroke to the injection during the compression stroke). The air-fuel ratio in the main combustion region including the in-cylinder residual fuel, the first injected fuel, and the second injected fuel can be made lean.
[0017]
According to the fifth aspect of the present invention, when fuel injection for main combustion is performed at least twice in total, the first fuel injection timing (from the late exhaust stroke to the mid-compression stroke) is advanced. Therefore, by the diffusion of the first injected fuel, the air-fuel ratio in the main combustion region including the in-cylinder residual fuel, the first injected fuel, and the second injected fuel can be made lean.
[0018]
According to the sixth aspect of the present invention, when performing fuel injection for main combustion at least twice in total, in order to reduce the amount of fuel injection for the second time (injection during the compression stroke), the residual fuel in the cylinder and the first time The air-fuel ratio in the main combustion region including the injected fuel and the second injected fuel can be made lean.
According to the seventh aspect of the present invention, when fuel injection for main combustion is performed at least twice in total, the fuel injection timing of the second time (injection during the compression stroke) is advanced, so By diffusion, the air-fuel ratio in the main combustion region including the in-cylinder residual fuel, the first injected fuel, and the second injected fuel can be made lean.
[0019]
According to the invention of claim 8 , the exhaust passage is provided with a NOx trap, and the injection of the additional fuel is performed to enrich the air-fuel ratio of the exhaust gas in order to desorb and purify NOx from the NOx trap. Thus, it is possible to appropriately control the ignition timing in the next cycle in which such rich spike control is performed, and perform NOx desorption purification without deteriorating operability.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a system diagram of an internal combustion engine (hereinafter referred to as an engine) showing a first embodiment of the present invention.
[0021]
The air taken into the engine 1 passes through the air cleaner 2, is measured by the air flow meter 3, and is guided to the electric throttle valve 4. Here, the intake air amount is controlled. The intake air is then guided to the cylinder 8 via the collector 5, the intake manifold 6, and the intake port 7. In the cylinder 8, the intake valve 10 is opened by the intake camshaft 9, and air is sucked together with the lowering of the piston 11.
[0022]
The fuel is supplied into the cylinder 8 by the fuel injection device 12. In this fuel injection device 12, fuel injection for mixture formation is performed once during the period from the late stage of the exhaust stroke through the intake stroke to the early stage of the compression stroke. In the latter half of the compression stroke, the fuel is injected once for a total of 2 times.
On the other hand, the air-fuel mixture is compressed by the rise of the piston 11, and the spark ignition device 13 ignites the ignition fuel that is the second injected fuel (first stage combustion by spark ignition). As a result, by increasing the pressure and temperature in the cylinder 8, the first injected fuel is self-ignited and combusted (second stage combustion), and the piston 11 is pushed down.
[0023]
After that, the exhaust valve 15 is opened by the exhaust camshaft 14, and the exhaust is discharged to the exhaust port 16 and further to the exhaust manifold 17 as the piston 11 rises. The exhaust manifold 17 is provided with an A / F sensor 18 for detecting an air-fuel ratio (hereinafter referred to as A / F), where the A / F in the exhaust is measured and the engine 1 is operated at an arbitrary A / F. In this case, feedback control is performed based on this signal.
[0024]
Exhaust gas that has passed through the exhaust manifold 17 is purified and discharged by a three-way catalyst 19 provided downstream thereof and a NOx trap 20 provided downstream thereof.
The three-way catalyst 19 has a characteristic of efficiently purifying HC, CO, NOx in the exhaust gas particularly when the exhaust A / F is stoichiometric.
The NOx trap 20 has a characteristic of trapping NOx in the exhaust when the exhaust A / F is lean, and desorbing and purifying the NOx trapped when the exhaust A / F is stoichiometric or rich. is there. Further, a NOx sensor 21 is provided downstream of the NOx trap 20, and NOx flowing out from the NOx trap 20 can be measured.
[0025]
Here, control of the throttle opening of the electric throttle valve 4 of the engine 1, control of the fuel injection timing and fuel injection amount of the fuel injection device 12, and control of the spark ignition timing of the spark ignition device 13 are performed by an engine control unit (hereinafter referred to as an engine control unit). (Referred to as ECU) 22.
The ECU 22 includes a signal from the air flow meter 3, a signal from the A / F sensor 18, a signal from the NOx sensor 21, a signal from a crank angle sensor for detecting a crank angle and an engine speed (not shown), an accelerator opening (depressing the accelerator pedal). (Quantity) A signal from an accelerator sensor for detection, a signal from an oil / water temperature sensor for detecting engine coolant temperature or an engine lubricating oil temperature, and the like are input, and the above-described controls are performed based on these signals.
[0026]
In such a self-ignition engine, since lean combustion is normally performed, reduction of NOx by the three-way catalyst 19 provided in the exhaust passage cannot be expected. Therefore, NOx discharged from the engine is trapped by the NOx trap 20 provided downstream.
However, since the amount of NOx traps by the NOx trap 20 has a limit, when the limit value is reached or before that, rich spike control must be performed to desorb and purify NOx from the NOx trap 20.
[0027]
The determination of the limit of the NOx trap amount, that is, the determination of the timing when the rich spike control is performed, uses a map in which the NOx emission amount is obtained in advance by experiments from the engine speed and the accelerator opening, for example, as shown in FIG. The NOx emission amount retrieved from this map may be integrated, and the integrated value may be determined depending on whether the limit value of the NOx trap amount has been reached, or a NOx sensor 21 provided downstream of the NOx trap 20 may be used. The detection may be performed by detecting that NOx has flowed downstream of the NOx trap 20. Of course, other conventional methods may be used and are not limited.
[0028]
When rich spike control is performed, additional fuel injection is performed from the fuel injection device 12 in the expansion stroke or exhaust stroke, and control is performed so that the exhaust A / F becomes stoichiometric or rich. Furthermore, the injection timing is set to a timing at which the oxidation reaction of the injected fuel does not sufficiently proceed and a timing at which a partial oxidation reaction occurs. As a method for determining the injection timing, for example, as shown in FIG. A map of the start timing of additional fuel injection may be created in advance by experiments from the engine speed and the accelerator opening, and may be searched from this, but other conventional methods may be used and are not limited.
[0029]
Here, first, the combustion control mode targeted by the present invention will be described.
In the next cycle in which the rich spike control is performed, the in-cylinder residual fuel concentration increases as compared to the normal operating condition. Further, since the residual fuel is exposed to a high temperature field, it is in a highly active state due to a partial oxidation reaction or the like. Therefore, in the next cycle in which the rich spike control is performed, if the same control as that in the normal operation condition in which the control is not performed is performed, the normal operation condition and the A / F in the main combustion region after the rich spike are illustrated in FIG. As is apparent from the characteristics of the self-ignition timing, ignition occurs early, and the engine performance deteriorates. Therefore, in order to obtain an appropriate ignition timing (an ignition timing equivalent to that under normal operating conditions), in the next cycle in which rich spike control is performed, the ignition timing is retarded by the ignition timing control means (early ignition timing). Need to be suppressed).
[0030]
In the present embodiment, as a means for retarding the ignition timing in the next cycle in which the rich spike control is performed, the first fuel injection amount is decreased from that in the normal operation condition, and the A / F in the main combustion region is reduced. The ignition timing is optimized by using a means for making the engine leaner than normal operating conditions. In this case, in the next cycle in which the rich spike control is performed, the in-cylinder residual fuel amount increases, and the residual fuel is in a highly active state as compared with the newly injected fuel. It is necessary to reduce more than the increase in quantity.
[0031]
FIG. 5 shows a control flow when rich spike control is performed in the present embodiment, FIG. 6 shows a time history of A / F in the main combustion region when the control is executed, and FIG. 6 shows changes in in-cylinder A / F. As shown in FIG. FIG. 6 shows the result under the condition that the additional fuel injection amount in the expansion stroke is gradually decreased in the rich spike control period. However, the control method of the additional fuel injection amount is limited to this. Not a thing.
[0032]
The control flow shown in FIG. 5 will be described below.
In S1, a correction value α for the first fuel injection amount Fw under normal operating conditions is calculated from each control parameter (accelerator opening, engine speed, additional fuel injection amount, oil / water temperature) (where α ≦ 1). ).
In S2, the first fuel injection amount Fw1 in the next cycle in which the rich spike control is performed is calculated from the following equation.
[0033]
Fw1 = α × Fw (where α ≦ 1)
As a result, the first fuel injection amount Fw1 is decreased, and the A / F in the main combustion region is made leaner than in the normal operation condition, so that the self-ignition timing can be optimized.
In S3, the end of rich spike control is determined. For example, as shown in FIG. 8, the end determination is performed using a map in which the NOx desorption reduction amount is obtained in advance by experiments from the engine speed and the additional fuel injection amount, and the NOx desorption reduction amount retrieved from this map. May be performed depending on whether or not the accumulated value has reached the NOx trap amount before the start of the rich spike control, or other conventional methods may be used.
In S4, when it is determined in S3 that the rich spike control is finished, the normal operation control is resumed.
[0034]
The present embodiment corresponds to the inventions of claims 1, 2 , 4 , and 8 , but by using the same control method as described above, the value of α is set as a correction value for the second fuel injection amount. It is also possible to optimize the ignition timing by reducing the fuel injection amount for the second time from the normal operating condition and making the A / F in the main combustion region leaner than the normal operating condition. This particularly corresponds to the invention of claim 6 .
Further, when compression self-ignition is performed by a piston (for example, an internal combustion engine described in Japanese Patent Application No. 2000-143850) instead of initial spark ignition, similar control is performed by changing α to an optimum value. It is possible to use a technique.
[0035]
Next, a second embodiment of the present invention will be described.
In the present embodiment, in the next cycle in which rich spike control is performed, as a means for retarding the ignition timing, the first fuel injection timing is advanced, and by the diffusion of the first injected fuel, the main combustion region By using means for making the A / F leaner than normal operating conditions, the ignition timing is optimized.
FIG. 9 shows a control flow when rich spike control is performed in this embodiment, and FIG. 10 shows changes in in-cylinder A / F when the control is executed.
[0036]
The control flow shown in FIG. 9 will be described below.
In S11, a correction value β for the first fuel injection timing I / T under normal operating conditions is calculated from each control parameter (accelerator opening, engine speed, additional fuel injection amount, oil / water temperature) (note that β ≧ 0).
In S12, the first fuel injection timing I / T1 in the next cycle in which the rich spike control is performed is calculated from the following equation.
[0037]
I / T1 = I / T-β (where β ≧ 0)
As a result, the first fuel injection timing I / T1 is advanced, and the A / F in the main combustion region is made leaner than during normal operating conditions, so that the self-ignition timing can be optimized. Become.
The processes in S13 and S14 are the same as those in the first embodiment (S3 and S4).
[0038]
This embodiment particularly corresponds to the inventions of claims 3 and 5 , but by using the same control method as described above, the value of β is set as a correction value for the second fuel injection timing, so that the second fuel is supplied. The injection timing is advanced from the normal operating condition, and the A / F in the main combustion region is made leaner than the normal driving condition by the diffusion of the injected fuel for the second time, thereby optimizing the ignition timing. It is also possible to plan. This particularly corresponds to the invention of claim 7 .
[0039]
Further, in the case where compression self-ignition is performed by a piston instead of the initial spark ignition (for example, an internal combustion engine described in Japanese Patent Application No. 2000-143850), the same control is performed by changing β to an optimum value. It is possible to use a technique.
[0040]
In the above, the case where additional fuel injection is performed in the expansion stroke or exhaust stroke in order to desorb and purify NOx trapped in the NOx trap has been described. For the purpose of increasing the temperature, additional fuel injection may be performed in the expansion stroke or the exhaust stroke, and the present invention can also be applied to this case.
[Brief description of the drawings]
FIG. 1 is a system diagram of an internal combustion engine showing a first embodiment of the present invention. FIG. 2 is a characteristic diagram of NOx emission. FIG. 3 is a characteristic diagram of an additional fuel injection start timing. FIG. 5 is a control flow chart of the first embodiment for the subsequent A / F in the main combustion region. FIG. 6 is a flowchart in the main combustion region when the rich spike control is performed in the first embodiment. FIG. 7 is a diagram showing the time history of / F. FIG. 7 is a diagram showing changes in in-cylinder A / F after normal operation conditions and rich spikes in the first embodiment. FIG. 8 is a characteristic diagram of NOx desorption reduction amount. 9] Control flowchart of the second embodiment [FIG. 10] A diagram showing changes in the in-cylinder A / F after the normal operation condition and the rich spike in the second embodiment.
1 engine
3 Air flow meter
4 Electric throttle valve
6 Intake manifold
8 cylinders
10 Intake valve
12 Fuel injector
13 Spark ignition device
15 Exhaust valve
17 Exhaust manifold
18 A / F sensor
19 Three-way catalyst
20 NOx trap
21 NOx sensor
22 ECU

Claims (8)

A self-ignition internal combustion engine that performs main combustion by self-igniting and burning at least a portion of the fuel injected into the cylinder, and is added to the cylinder in the expansion stroke or exhaust stroke under predetermined operating conditions For fuel injection,
In the next cycle in which the injection of the additional fuel is performed, the air-fuel ratio including the residual fuel and the newly injected fuel in the main combustion region, which is the ignition start region at the time of main combustion , is ignited at the same level as that under normal operating conditions. A self-igniting internal combustion engine characterized by being made leaner than the air-fuel ratio under normal operating conditions so as to obtain timing . In a self-ignition internal combustion engine that performs fuel injection for main combustion at least once during an intake stroke to a compression stroke,
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region is for reducing the fuel injection amount for main combustion. In a self-ignition internal combustion engine that performs fuel injection for main combustion at least once during an intake stroke to a compression stroke,
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region advances the fuel injection timing for main combustion. In a self-ignition internal combustion engine that performs fuel injection for main combustion at least twice in total during the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke.
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region reduces the first fuel injection amount. In a self-ignition internal combustion engine that performs fuel injection for main combustion at least twice in total during the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke.
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region is for advancing the first fuel injection timing. In a self-ignition internal combustion engine that performs fuel injection for main combustion at least twice in total during the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke.
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region is for reducing the second fuel injection amount. In a self-ignition internal combustion engine that performs fuel injection for main combustion at least twice in total during the compression stroke, once during the period before the exhaust stroke and before the injection during the compression stroke.
2. The self-ignition internal combustion engine according to claim 1 , wherein the means for leaning the air-fuel ratio in the main combustion region advances the second fuel injection timing. The exhaust passage includes a NOx trap that traps NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and desorbs and purifies NOx trapped when the air-fuel ratio is stoichiometric or rich,
The injection of additional fuel, in order to desorption purify NOx from the NOx trap, wherein the air-fuel ratio of the exhaust gas to one of claims 1 to 7, characterized in that to enrich Self-igniting internal combustion engine.

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