JP2010133283A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine controlling ignition-combustion timing for HCCI (Homogeneous Charge Compression Ignition) combustion in a six-cycle internal combustion engine. <P>SOLUTION: In the six-cycle internal combustion engine sequentially performing an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke, SI (Spark Ignition) combustion by spark ignition is performed from the intake stroke to the first expansion stroke, additional fuel is injected into burnt gas generated by the SI combustion, and the HCCI combustion by compression self-ignition is performed before the second expansion stroke is ended. Timing with a combustion rate when performing the HCCI combustion set to a predetermined rate is calculated based on detected cylinder pressure, and a comparison value between a calculated value and a required value is feedback-corrected at spark ignition timing in the SI combustion so that the calculated value agrees with the required value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly, to a control device for an internal combustion engine suitable for executing control of a six-cycle internal combustion engine mounted on a vehicle.

  Conventionally, as disclosed in, for example, Patent Document 1, one combustion cycle is completed in a total of six strokes: intake stroke → first compression stroke → first expansion stroke → second compression stroke → second expansion stroke → exhaust stroke A direct-injection engine having 6 strokes and 1 cycle (hereinafter referred to as 6 cycles) is known. In addition, this publication discloses a first combustion process in which fuel is burned SI (Spark Ignition) at a lean air-fuel ratio through the intake stroke → first compression stroke → first expansion stroke. Further, the additional fuel is injected into the burned gas generated in the first combustion process, and the additional fuel is combusted through HCCI (Homogeneous Charge Compression Ignition) through the second compression stroke → the second expansion stroke. A second combustion process is disclosed. According to such a configuration, while performing the intake / exhaust stroke with a pumping loss once, the combustion that generates the output can be performed twice, so that the fuel efficiency can be improved. Further, since the re-reaction of unburned gas is promoted in the second combustion process, the exhaust gas performance can be enhanced.

JP 2001-336435 A JP 2002-276442 A JP-A-2005-139985 JP 2001-355484 A

  By the way, in the above-described HCCI combustion in the second combustion process, the premixed mixture of fuel and air is ignited and combusted at each point where it reaches the self-ignition temperature through the second compression stroke. However, this ignition / combustion period is affected by the outside air temperature, the combustion chamber temperature, the residual gas temperature, and the like. Therefore, in the conventional internal combustion engine described above, there is a variation in ignition / combustion timing for self-ignition in HCCI combustion, which may lead to a decrease in fuel efficiency and exhaust gas performance due to knocking or misfire.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can control ignition / combustion timing of HCCI combustion in a 6-cycle internal combustion engine.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A six-cycle internal combustion engine that sequentially executes an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke;
A fuel injection valve for injecting fuel;
A spark plug that sparks the injected fuel,
An in-cylinder pressure sensor for detecting the in-cylinder pressure;
SI combustion means for spark-igniting the spark plug after injecting fuel into the fuel injection valve during the period from the intake stroke to the first expansion stroke;
HCCI combustion means for injecting additional fuel into burned gas generated by the SI combustion means, and then compressing and self-igniting the additional fuel until the second expansion stroke;
Calculating means for calculating a timing at which the combustion ratio during HCCI combustion becomes a predetermined ratio based on the in-cylinder pressure;
Request value acquisition means for acquiring a request value at a time when the combustion ratio during HCCI combustion becomes the predetermined ratio;
Feedback correction means for feedback correcting the comparison value between the calculated value and the required value to the spark ignition timing of the SI combustion means so that the calculated value calculated by the calculating means matches the required value. It is characterized by.

  According to the first aspect of the invention, the comparison result between the calculated value and the required value is calculated using the SI combustion so that the calculated value calculated from the in-cylinder pressure at which the combustion rate at the time of HCCI combustion becomes a predetermined rate matches the required value. Feedback correction can be made to the spark ignition timing in the means. By performing feedback correction of the spark ignition timing in the SI combustion means, the second compression stroke start temperature can be adjusted, and the ignition / combustion timing in HCCI combustion can be controlled.

  Specifically, when the calculated value is larger than the required value (that is, the calculated combustion timing is later), the spark ignition timing in SI combustion is retarded, and then the second compression stroke starts. The period until the second compression stroke can be shortened, and the second compression stroke start temperature can be increased. By increasing the second compression stroke start temperature, the additional fuel can be easily subjected to compression self-ignition at multiple points, and the combustion timing in HCCI combustion can be advanced. On the other hand, when the calculated value is smaller than the required value (that is, the calculated combustion timing is earlier), the spark ignition timing in SI combustion is advanced, and thereafter the period until the start of the second compression stroke Can be lengthened, and the second compression stroke start temperature can be lowered. By lowering the second compression stroke start temperature, the additional fuel is less likely to undergo compression self-ignition, and the combustion timing in HCCI combustion can be delayed. Thus, according to the present invention, the ignition / combustion timing in HCCI combustion can be optimally controlled by feeding back the comparison result between the calculated value and the required value to the spark ignition timing in SI combustion.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system according to the first embodiment includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 has a plurality of cylinders, and FIG. 1 shows a cross section of one of the cylinders. A piston provided in each cylinder is connected to a crankshaft via a crank mechanism. A crank angle sensor 12 for detecting the crank angle CA is provided in the vicinity of the crankshaft. A combustion chamber 14 is formed in each cylinder. An ignition plug 16, an in-cylinder pressure sensor 18, and an in-cylinder injector 20 are disposed in the combustion chamber 14. An intake passage 22 and an exhaust passage 24 are connected to the combustion chamber 14.

  An air flow meter 26 is disposed upstream of the intake passage 22. A throttle valve 28 is disposed downstream of the air flow meter 26. A surge tank 30 is provided downstream of the throttle valve 28. An electromagnetically driven intake valve 32 that opens and closes the intake passage 22 with respect to the combustion chamber 14 is provided at the downstream end of the intake passage 22.

  An electromagnetically driven exhaust valve 34 that opens and closes the exhaust passage 24 with respect to the combustion chamber 14 is provided at the upstream end of the exhaust passage 24. Further, an exhaust purification catalyst (not shown) is provided downstream of the exhaust valve 34.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 50. The crank angle sensor 12, the in-cylinder pressure sensor 18, the air flow meter 26, and the like are connected to the input side of the ECU 50. The aforementioned ignition plug 16, injector 20, electromagnetically driven intake valve 32 and exhaust valve 34 are connected to the output side of the ECU 50. Further, the ECU 50 calculates the engine speed NE based on the crank angle CA.

  Further, the ECU 50 controls the spark plug 16, the injector 20, the electromagnetically driven intake valve 32 and the exhaust valve 34, thereby realizing an SI (Spark Ignition) operation mode and an SI + HCCI (Homogeneous Charge Compression Ignition) operation mode. The control routine for storing is stored. In the SI operation mode, a general 4-stroke 1-cycle operation (hereinafter referred to as 4 cycles) is performed in which one cycle is performed by four strokes of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. On the other hand, in the SI + HCCI operation mode, as will be described in detail later, a 6-stroke 1-cycle operation (hereinafter referred to as 6 cycles) is performed in which each of the compression stroke and the expansion stroke is performed twice during one cycle.

  The six-cycle operation of this embodiment will be described in detail. FIG. 2 is a time chart showing the operation in the SI + HCCI 6-cycle operation in the first embodiment. In the six-cycle operation of the present embodiment, as shown in FIG. 2, (a) intake stroke, (b) first compression stroke, (c) first expansion stroke, (d) second compression stroke, (e) second The six strokes of the expansion stroke and (f) the exhaust stroke are sequentially executed. Further, in the six-cycle operation of the present embodiment, two combustion processes, that is, a first combustion process based on spark ignition mainly composed of stratified combustion and a second combustion process based on compression self-ignition mainly composed of uniform combustion, are included in one cycle. Is going on.

  First, in the first combustion process, during the period from (a) the intake stroke to (c) the first expansion stroke, the fuel is injected into the injector 20 and then the ignition plug 16 is spark-ignited to perform SI combustion of the injected fuel. Is realized. Specifically, in the first combustion process described above, as shown in FIG. 2, (b) the injector 20 performs the first fuel injection during the first compression stroke. After the first fuel injection, (b) spark ignition is performed on the spark plug 16 immediately before the top dead center of the first compression stroke. As a result, the injected fuel undergoes SI combustion and the in-cylinder pressure increases. Thereafter, (c) the in-cylinder pressure decreases as SI combustion stops in the second half of the first expansion stroke. The first fuel injection may be performed during (a) the intake stroke, and the spark ignition may be performed during (c) the first expansion stroke.

  Further, in the second combustion process, additional fuel is injected into the burned gas generated in the first combustion process, and then (e) the additional fuel is compressed and self-ignited until the second expansion stroke. Combustion is realized. Specifically, in the second combustion process described above, as shown in FIG. 2, (c) injection of additional fuel (hereinafter referred to as second fuel injection) is performed during the first expansion stroke. Thereafter, without causing the spark plug 16 to perform spark ignition, the additional fuel and the unburned gas are compressed and self-ignited during (d) the second compression stroke and (e) the second expansion stroke. As a result, the additional fuel and unburned fuel are HCCI burned and the in-cylinder pressure is greatly increased. Thereafter, (e) the in-cylinder pressure decreases as the HCCI combustion stops over the latter half of the second expansion stroke. The second fuel injection may be performed during (d) the second compression stroke.

  Here, the total amount of the injected fuel in the first fuel injection and the second fuel injection described above is controlled by the sum of the fuel injection amounts with respect to the intake air amount GA sucked in the intake stroke (for example, controlled to the theoretical air-fuel ratio). ) In the present embodiment, 1/2 fuel is injected by the first fuel injection (that is, the in-cylinder equivalence ratio is 0.5), and the remaining 1/2 fuel is injected by the second fuel injection. (I.e., the in-cylinder equivalence ratio is 1.0) and the six-cycle operation is performed. According to such injection control, SI is burned at a lean air-fuel ratio in the first combustion process of the present embodiment.

[Characteristic Control in Embodiment 1]
By the way, in the above-described HCCI combustion in the second combustion process, the premixed mixture of fuel and air self-ignites and burns at each point where the pre-ignition gas reaches the self-ignition temperature through (d) the second compression stroke. However, this ignition / combustion period is affected by the outside air temperature, the combustion chamber temperature, the residual gas temperature, and the like. Therefore, in the SI + HCCI 6-cycle operation described above, the ignition / combustion timing varies, particularly in a transient state, simply by performing open control using an operation map that defines the spark ignition timing corresponding to the engine load and the engine speed. Variations in ignition / combustion timing may cause knocking or misfire, which may lead to a reduction in fuel efficiency and exhaust gas performance. Therefore, optimal control of the combustion timing in HCCI combustion is desirable for improving fuel efficiency and exhaust gas performance.

  Therefore, in the system of the present embodiment, in order to optimally control the combustion timing in HCCI combustion, the spark ignition timing in SI combustion is corrected by feedback (PID) control.

  A more specific outline of control will be described with reference to FIG. FIG. 3 is a block diagram for explaining feedback control used in the first embodiment. 3 corresponds to the internal combustion engine 10 of FIG. 1 (in particular, the combustion chamber 14 and the spark plug 16), and the “in-cylinder pressure sensor 62” corresponds to the in-cylinder pressure sensor 18 of FIG. ing.

  The ECU 50 stores an operation map 64 that defines a reference spark ignition timing according to the engine speed NE and the engine load. The “reference spark ignition timing 66” is selected by open control using the operation map 64. Thereafter, a “new spark ignition timing 70” is determined by adding a “feedback correction value 68” described later to the selected “reference spark ignition timing 66”. Then, after the above-described first fuel injection is performed in the internal combustion engine 10, the spark plug 16 is spark-ignited according to “new spark ignition timing 70”, and the injected fuel is SI burned. Then, after implementing the 2nd fuel injection mentioned above, it carries out compression self-ignition and carries out HCCI combustion of additional fuel and unburned gas.

  A change in the in-cylinder pressure due to HCCI combustion is detected by the in-cylinder pressure sensor 18 synchronized with the crank angle CA. The ECU 50 calculates a timing (hereinafter referred to as “HCCI combustion timing calculation value 72”) when the combustion ratio during HCCI combustion becomes a predetermined ratio (here, 50%) from the detected in-cylinder pressure.

  On the other hand, the ECU 50 acquires a control request value (hereinafter referred to as “HCCI combustion timing control request value 74”) at which the combustion ratio during HCCI combustion becomes a predetermined ratio (here, 50%). Note that the ECU 50 stores a control request map that defines HCCI combustion timing control request values according to the engine speed NE, engine load, and the like.

  Then, the ECU 50 sets the “HCCI combustion timing calculated value 72” and the “HCCI combustion timing control required value 74” so that the “HCCI combustion timing calculated value 72” matches the “HCCI combustion timing control required value 74”. And the error is calculated as “feedback correction value 68”. Then, feedback control is performed by adding the calculated “feedback correction value 68” to the next “reference spark ignition timing 66” to obtain “new spark ignition timing 70”. Thereafter, the internal combustion engine 10 is operated in accordance with “new spark ignition timing 70”.

  FIG. 4 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described operation. In the routine shown in FIG. 4, first, in step 100, the ECU 50 determines whether the required operation region is the SI4 cycle operation region or the SI + HCCI 6 cycle operation region based on the acquired engine speed NE and the engine load. to decide. Here, the ECU 50 stores an operation region map that defines an SI4 cycle operation region and an SI + HCCI 6 cycle operation region in accordance with the engine speed NE and the engine load. If it is determined that the current position is in the SI4 cycle operation region, the SI4 cycle operation is performed in step 110, and then this routine is terminated.

  On the other hand, if it is determined in step 100 described above that this is the SI + HCCI 6-cycle operation region, then in step 120, the SI + HCCI 6-cycle operation shown in FIG.

  Subsequently, in step 130, the in-cylinder pressure at the time of HCCI combustion in each cycle is detected by the in-cylinder pressure sensor 18 synchronized with the crank angle CA. Then, the “HCCI combustion timing calculation value 72” shown in FIG. 3 described above, which is the timing at which the combustion ratio during HCCI combustion becomes 50%, is calculated from the past in-cylinder pressure.

  Further, in step 140, the “HCCI combustion timing calculated value 72” and the “HCCI combustion timing 72” shown in FIG. 3 are matched with the “HCCI combustion timing control required value 74”. A “feedback correction value 68” is calculated for feedback correction (PID control) of the error from the “control request value 74” to the next spark ignition timing. Then, the calculated “feedback correction value 68” is added to the next “reference spark ignition timing 66” determined by the open control using the operation map 64, and the “new spark ignition timing 70” in the next SI combustion is added. Implement the specified feedback control.

  As described above, according to the routine shown in FIG. 4, the comparison result is obtained so that the “HCCI combustion timing calculated value 72” calculated from the in-cylinder pressure matches the “HCCI combustion timing control required value 74”. Can be feedback corrected to the spark ignition timing in SI combustion. FIG. 5 is a relationship diagram showing the relationship among the spark ignition timing, the second compression stroke start temperature (solid line), and the HCCI 50% combustion timing (broken line) in SI combustion. According to the system of this embodiment, as shown in FIG. 5, the second compression stroke start temperature can be adjusted by advancing / retarding the spark ignition timing in SI combustion by feedback correction. The ignition / combustion timing in HCCI combustion can be controlled to coincide with the control request value.

  Specifically, when the “HCCI combustion timing calculated value 72” is larger than the “HCCI combustion timing control required value 74” (that is, the calculated combustion timing is later), as shown in FIG. By retarding the spark ignition timing in combustion, the period until the start of the second compression stroke can be shortened thereafter, and the second compression stroke start temperature can be increased. By increasing the second compression stroke start temperature, the additional fuel can be easily subjected to compression self-ignition at multiple points, and the combustion timing in HCCI combustion can be advanced.

  On the other hand, when the “HCCI combustion timing calculated value 72” is smaller than the “HCCI combustion timing control required value 74” (that is, the calculated combustion timing is earlier), as shown in FIG. By advancing the ignition timing, the period until the start of the second compression stroke can be extended thereafter, and the second compression stroke start temperature can be lowered. By lowering the second compression stroke start temperature, it becomes difficult for the additional fuel to undergo compression self-ignition, and the combustion timing in HCCI combustion can be delayed.

  Thus, according to the system of the present embodiment, in the 6-cycle operation, the ignition / combustion timing in HCCI combustion can be matched with the control request value by feedback control of the spark ignition timing in SI combustion. Can achieve excellent fuel efficiency and exhaust gas performance.

In the first embodiment described above, the injector 20 is the “fuel injection valve” in the first invention, the spark plug 16 is the “ignition plug” in the first invention, and the in-cylinder pressure sensor 18 is the first engine. This corresponds to the “cylinder pressure sensor” in the first aspect of the invention.
Further, here, the ECU 50 performs the first combustion process, so that the “SI combustion means” in the first invention performs the second combustion process, and the “HCCI combustion in the first invention”. The “means” executes the process of step 130, so that the “calculation means” in the first invention executes the process of step 140, thereby “request value acquisition means” and “ The “feedback correction means” is realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. 3 is a time chart showing an operation in SI + HCCI 6-cycle operation in the first embodiment. 4 is a block diagram for explaining feedback control used in Embodiment 1. FIG. 3 is a flowchart of a control routine executed by an ECU 50 in the first embodiment. FIG. 6 is a relationship diagram illustrating a relationship among an SI combustion spark ignition timing, a second compression stroke start temperature, and an HCCI 50% combustion timing in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Crank angle sensor 16 Spark plug 18 In-cylinder pressure sensor 20 Injector 22, 24 Intake passage, exhaust passage 32, 34 Intake valve, exhaust valve 50 ECU (Electronic Control Unit)

Claims (1)

A six-cycle internal combustion engine that sequentially executes an intake stroke, a first compression stroke, a first expansion stroke, a second compression stroke, a second expansion stroke, and an exhaust stroke;
A fuel injection valve for injecting fuel;
A spark plug that sparks the injected fuel,
An in-cylinder pressure sensor for detecting the in-cylinder pressure;
SI combustion means for spark-igniting the spark plug after injecting fuel into the fuel injection valve during the period from the intake stroke to the first expansion stroke;
HCCI combustion means for injecting additional fuel into the burned gas generated by the SI combustion means and then compressing and self-igniting the additional fuel until the second expansion stroke;
Calculating means for calculating a timing at which the combustion ratio during HCCI combustion becomes a predetermined ratio based on the in-cylinder pressure;
Request value acquisition means for acquiring a request value at a time when the combustion ratio during HCCI combustion becomes the predetermined ratio;
Feedback correction means for feedback correcting the comparison value between the calculated value and the required value to the spark ignition timing of the SI combustion means so that the calculated value calculated by the calculating means matches the required value;
A control device for an internal combustion engine, comprising:

Images