JP2013241916A - Combustion control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a knock limit by increasing an EGR (Exhaust Gas Recirculation) amount in an operation region where knocking is liable to occur.SOLUTION: An EGR port 13b communicating with an exhaust passage 13 is formed in a combustion chamber 3; and an EGR gas direct current valve 22 is provided in the EGR port 13b. When an ECU 31 determines that an operation region of an engine is in a partial load knocking region, the ECU actuates a VVT (Variable Valve Timing) actuator 19 to set a valve timing in such a way that a phase of an intake cam 15 for opening and closing an intake valve 6 is delayed and that the intake valve 6 is opened after an exhaust valve 7 is closed and has passed over the intake top dead center TDC. In a period from the intake top dead center TDC to immediately after the intake valve 6 is opened, the ECU 31 further applies a control current to an EGR coil 23 that opens and closes the EGR port 13b so as to open the EGR port 13b and to supply EGR gas to the combustion chamber 3.

Description

  The present invention relates to an engine combustion control apparatus in which EGR gas is supplied to a combustion chamber to avoid knocking when it is determined that the engine operating region is a knock region.

  Increasing the compression ratio is known as one of means for improving the fuel consumption of an engine. However, if the compression ratio of the engine is set high, knocking is likely to occur even in the partial load region, particularly in the low / medium rotation / high load region (hereinafter referred to as “partial load region where knocking is likely to occur”). Referred to as “load knock region”).

  As means for avoiding knocking in such a region, it is common to retard the ignition timing (retard) or lower the effective compression ratio, but the maximum combustion pressure in the combustion chamber becomes lower, There is an inconvenience that the heat efficiency is lowered and the output is lowered.

  As a countermeasure, a technology is known in which EGR (Exhaust Gas Recirculation) gas is supplied into the combustion chamber during high-load operation to suppress an increase in the compression end temperature in the combustion chamber and to avoid knocking without reducing the thermal efficiency. .

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-332591), an EGR gas introduction valve that is driven to open and close by an EGR gas introduction valve cam provided on an intake camshaft is disposed adjacent to the intake valve, and A technique is disclosed in which EGR gas is directly introduced into the combustion chamber during the stroke.

JP 2004-332591 A

  By the way, as described above, the operation region where knocking is likely to occur is the low / medium rotation / high load operation region, and when EGR gas is directly supplied to the combustion chamber in this region where knocking does not occur, the oxygen concentration in the combustion chamber is low. Since it falls, combustion tends to become unstable.

  In the technique disclosed in the above-described document, since the EGR gas introduction valve is opened and closed by the EGR gas introduction valve cam provided on the intake camshaft, EGR gas is constantly supplied into the combustion chamber during the intake stroke. In the operation region other than the knock generation region, an EGR amount more than necessary is supplied to the combustion chamber, and there is a disadvantage that combustion becomes unstable and exhaust emission deteriorates.

  In view of the above circumstances, the present invention improves the knock limit by increasing the EGR amount in the operation region where knocking is likely to occur, and stabilizes combustion without supplying more EGR gas than necessary in the region where knocking is difficult to occur. An object of the present invention is to provide an engine combustion control device that can realize the above.

  An engine combustion control apparatus according to the present invention includes a valve timing variable mechanism that allows variable valve timing of an intake valve, an EGR passage that communicates an exhaust passage and a combustion chamber, and an EGR valve mechanism that opens and closes the EGR passage. And a control means for controlling the operation of the valve timing variable mechanism section and the EGR valve mechanism section, wherein the control means determines a knock area based on an operating state of the engine, and the knock area An intake valve timing setting means for setting a region in which the in-cylinder pressure decreases during an intake stroke by displacing the valve timing of the intake valve by the valve timing variable mechanism when the determination means determines that it is a knock region; An EGR tie that opens the EGR valve mechanism in a region where the in-cylinder pressure set by the timing setting means decreases. And a ring setting means.

  According to the present invention, the knock limit can be improved because the EGR gas is directly supplied to the combustion chamber to increase the EGR amount only when the engine operating region is the knock region. Moreover, since the supply of EGR gas is limited in the region where knocking is difficult to occur, stabilization of combustion can be realized.

1 is a schematic configuration diagram of an engine control system according to a first embodiment. The flowchart showing the intake timing variable control routine The flowchart which shows the same EGR gas DC valve control routine Same as above, illustration of partial load knock region map (A) is a time chart showing changes in in-cylinder pressure, (b) is a time chart showing valve timings of an intake valve and an exhaust valve, and (c) is a time chart showing valve timings of an EGR gas DC valve. The flowchart which shows the intake timing variable control routine by 2nd Embodiment (A) is a time chart showing the change in the cylinder pressure, (b) is a time chart showing the valve timing of the intake valve, and (c) is a time chart showing the valve timing of the EGR gas DC valve.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
1 to 5 show a first embodiment of the present invention. 1, reference numeral 1 denotes an engine body, 2 a piston, 3 a combustion chamber, 4 an intake port, 5 an exhaust port, 6 an intake valve, 7 an exhaust valve, and an intake passage 8 communicating with the intake port 4. A throttle valve 9 is interposed, and an air cleaner 10 is disposed upstream of the intake passage 8. Further, an injector 11 that directs the injection direction to the intake valve 6 is fixed to the intake port 4, and an ignition portion of the spark plug 12 faces one side of the combustion chamber 3. Further, an exhaust passage 13 communicates with the downstream end of the exhaust port 5, a catalyst 14 for purifying exhaust gas is interposed upstream of the exhaust passage 13, and a muffler (not shown) is disposed downstream thereof. Has been.

  The intake valve 6 that opens and closes the intake port 4 and the exhaust valve 7 that opens and closes the exhaust port 5 are an intake cam 15 connected to the intake cam shaft 15a, and an exhaust cam 16 pivotally attached to the exhaust cam shaft 16a. Is opened and closed. The camshafts 15a and 16a rotate at a half speed with respect to the crankshaft.

  The intake cam 15 is connected to the intake cam shaft 15a via a variable valve timing (VVT) actuator 19 serving as a valve timing variable mechanism. The VVT actuator 19 changes the cam phase (cam displacement angle) of the intake cam 15 by the hydraulic pressure regulated by the hydraulic control valve 21. When the cam phase of the intake cam 15 changes, the valve opening timing of the intake valve 6 that is opened and closed by the intake cam 15 is varied.

  One end of the EGR passage 13 a communicates with the upstream side of the catalyst 14 in the exhaust passage 13, and an EGR port 13 b provided at the other end of the EGR passage 13 a is opened at the center of the top surface of the combustion chamber 3. The EGR port 13b is formed almost directly from the center of the top surface, and an EGR passage 13a communicates with one end of the EGR port 13b.

  The EGR port 13b is provided with an EGR gas DC valve 22 as an EGR valve, and the EGR port 13b is opened and closed by the advance / retreat operation of the EGR gas DC valve 22. The EGR gas DC valve 22 is an electromagnetic valve, and is normally urged in a valve closing direction by a valve spring (not shown). The EGR gas DC valve 22 is energized in the valve opening direction by energizing an EGR coil 23 as an electromagnetic coil. The EGR gas DC valve 22 and the EGR coil 23 constitute an EGR valve mechanism portion of the present invention.

  The hydraulic control valve 21 and the EGR coil 23 are controlled by an operation signal from an electronic control unit (ECU) 31 as control means. The ECU 31 is mainly composed of a well-known microcomputer comprising a CPU, ROM, RAM, etc., and outputs drive signals to the hydraulic control valve 21 and the EGR coil 23 according to a control program stored in advance in the CPU. To do.

  On the input side of the ECU 31, an intake air amount sensor 24 that is disposed immediately downstream of the air cleaner 10 and detects the intake air amount Q supplied to the combustion chamber 3, is disposed upstream of the catalyst 14 and is connected to the catalyst 14. An air-fuel ratio sensor 25 for detecting the air-fuel ratio from the degree of oxygen in the exhaust gas flowing in is connected. Further, on the input side of the ECU 31, the engine speed sensor 26 for detecting the engine speed Ne, and the rotation of the camshaft 15a (or 16a) that rotates at a half speed of the crankshaft are detected. In the embodiment, for example, a cam angle sensor 27 for calculating a cam angle θCAM based on the intake top dead center TDC is connected.

  The ECU 31 examines the engine operating region based on the parameters detected by each sensor, and when in the partial load knock region, the ECU 31 displaces the valve opening timing of the intake cam 15 in the retarded direction, and delays and opens the valve slowly. A section in which the valve overlap is eliminated, the exhaust valve 7 and the intake valve 6 are both closed near the intake top dead center TDC, and the EGR gas DC valve 22 is set in a section in which the valves 6 and 7 are closed. Is opened, EGR gas is directly supplied using the negative pressure generated in the combustion chamber 3, and combustion in the combustion chamber 3 is controlled.

  Specifically, the combustion control executed by the ECU 31 is processed by an intake cam phase control routine shown in FIG. 2 and an EGR gas DC valve control routine shown in FIG. Both these routines are executed every set calculation cycle after turning on the ignition switch.

  The intake cam phase control routine shown in FIG. 2 first reads the intake air amount Q detected by the intake air amount sensor 24 and the engine speed Ne detected by the engine speed sensor in step S1.

  Next, the process proceeds to step S2, and the current operation region is examined by referring to the region determination map with interpolation calculation based on the intake air amount Q and the engine speed Ne. FIG. 4 shows a conceptual diagram of the area determination map. It is known that there is a region (partial load knock region) where knocking is likely to occur even in the operation region (partial load region) when the throttle valve 9 is not fully opened. In the area determination map, an area where knocking is likely to occur even if it is a partial load is specified in advance through experiments or the like, and the value (for example, 1 for the knocking area and 0 for the other areas) is stored.

  And it progresses to step S3, it is determined whether the said driving | running | working area | region is a partial load knock area | region, when it remove | deviates from the partial load knock area | region, it progresses to step S4, and in the partial load knock area | region, it progresses to step S5. Note that the processing in steps S2 and S3 corresponds to the knock region determination means of the present invention.

  In step S4, the partial load knock region determination flag FG is cleared (FG ← 0), and in step S6, the control current value IVT for driving the hydraulic control valve 21 is set to a preset normal valve timing. The normal value IVTN is set (IVT ← IVTN), and the process proceeds to step S8.

  In step S5, the partial load knock region determination flag FG is set (FG ← 1). In step S7, the control current value IVT for driving the hydraulic control valve 21 is set to a preset EGR gas. The delay angle value IVTR, which is the valve timing for setting the DC region, is set (IVT ← IVTR), and the process proceeds to step S8. The process in step S7 corresponds to the intake valve timing setting means of the present invention.

  Then, when the process proceeds from step S6 or step S7 to step S8, the control current value IVT is set and the routine is exited.

  The ECU 31 outputs a drive signal corresponding to the control current value IVT to the hydraulic control valve 21 via a drive circuit (not shown). The hydraulic control valve 21 outputs a hydraulic pressure corresponding to the control current value IVT to the VVT actuator 19. The VVT actuator 19 varies the phase (displacement angle) of the intake cam 15 in accordance with the hydraulic pressure supplied from the hydraulic control valve 21.

  Then, the valve timing of the intake valve 6 that is opened and closed by the intake cam 15 is varied, and when the control current value IVT is set to the normal value IVTN as shown in FIG. As indicated by the solid line, the valve timing is set such that the exhaust valve 7 opens with a predetermined valve overlap. In this embodiment, the valve lift amounts of both valves 6 and 7 are set to coincide with each other at the intake top dead center TDC.

  On the other hand, when the control current value IVT is set to the retard value IVTR, the intake valve 6 is opened immediately after the exhaust valve 7 is closed as shown by the broken line in FIG. A section in which both valves 6 and 7 are closed occurs. Then, as indicated by a broken line in FIG. 5A, the in-cylinder pressure is lowered until fresh air is introduced into the combustion chamber 3 by opening the intake valve 6 at the beginning of the intake stroke.

  In the EGR gas DC valve control routine shown in FIG. 3, first, in step S11, the value of the partial load knock region determination flag FG set in the intake cam phase control routine described above is read. When FG = 1, it is determined that the operation region is in the partial load knock region, and the process proceeds to step S12. On the other hand, if FG = 0, the routine is exited. Therefore, when FG = 0, the EGR port 13b is closed by the EGR gas DC valve 22 that is always urged in the valve closing direction via a valve spring (not shown).

  In step S12, the cam angle θCAM [° CA (crank angle)] with the intake top dead center TDC detected by the cam angle sensor 27 as a reference is read. Next, the process proceeds to step S13, and it is checked whether or not the cam angle θCAM has reached a preset valve opening angle θOPN. In this embodiment, the valve opening angle θOPN is set to the intake top dead center TDC, which is the reference cam angle.

  If the cam angle θCAM has not yet reached the valve opening angle θOPN, the process returns to step S12 and waits until the cam angle θCAM reaches the valve opening angle θOPN. On the other hand, when the cam angle θCAM reaches the valve opening angle θOPN, the process proceeds to step S14.

  In step S14, energization of the control current to the EGR coil 23 is started, and the EGR gas DC valve 22 is opened against the urging force of a valve spring (not shown) (see FIG. 5C). ). Then, due to the pressure difference between the internal pressure of the combustion chamber 3 at the end of the intake stroke and the internal pressure of the intake passage 8 upstream of the catalyst 14, a part of the exhaust gas passes through the EGR passage 13a and becomes EGR gas from the EGR port 13b as the combustion chamber 3 Supplied in.

  Next, the process proceeds to step S15, and the cam angle θCAM is read again. In step S16, it is checked whether or not the cam angle θCAM has reached a preset valve closing angle θCLS. In the present embodiment, the valve opening period of the EGR gas DC valve 22 is set to a section in which the in-cylinder pressure at the initial stage of the intake stroke is low, as indicated by a broken line in FIG. Specifically, the valve closing angle θCLS is symmetric with respect to the intake top dead center TDC (θCAM = θOPN) immediately after the intake cam 15 starts opening, that is, with the position where the intake valve 6 starts to open. Is set to the correct position.

  If the cam angle θCAM has not yet reached the valve closing angle θCLS, the process returns to step S15 and waits until the cam angle θCAM reaches the valve closing angle θCLS. On the other hand, when the cam angle θCAM reaches the valve closing angle θCLS, the process proceeds to step S17.

  In step S17, energization to the EGR coil 23 is interrupted, the EGR gas DC valve 22 is closed by the urging force of the valve spring (see FIG. 5C), and the routine is exited. As a result, the supply of EGR gas to the combustion chamber 3 is shut off. The processing performed in the routine shown in FIG. 3 corresponds to the EGR timing setting means of the present invention.

  Thus, in this embodiment, when the engine operating state is in the partial load knock region, the valve timing of the intake valve 6 is retarded and the valve opening timing is set immediately after the exhaust valve 7 is closed. Therefore, the internal pressure of the combustion chamber 3 temporarily decreases. Since the EGR gas DC valve 22 is opened at that timing, the internal pressure of the combustion chamber 3 and the intake passage on the upstream side of the catalyst 14 are introduced before fresh air is introduced into the combustion chamber 3 at the beginning of the intake stroke. 8, the exhaust gas can be instantaneously supplied to the combustion chamber 3 as EGR gas from the EGR port 13b through the EGR passage 13a. As a result, the combustion temperature is lowered by the EGR gas, and knocking is avoided. Accordingly, the ignition timing can be set relatively to the MBT (Minimum spark advance for Best Torque) side, and even in a high compression ratio engine, the knock limit can be improved and high thermal efficiency can be obtained.

  Further, even in the partial load region, the EGR gas is not directly supplied in a region where knocking is difficult to occur, so that stable combustion can be obtained.

[Second Embodiment]
6 and 7 show a second embodiment of the present invention. In this embodiment, when the engine operating region is in the partial load knock region, the valve opening timing of the intake valve 6 is displaced in the advance direction to set the valve to open quickly and close immediately, and immediately after the intake valve 6 is closed. The EGR gas DC valve 22 is opened to allow EGR gas to flow into the combustion chamber 3. The valve timing of the intake valve 6 and the EGR gas DC valve 22 is different between the present embodiment and the first embodiment described above. In addition, since the structure of the engine periphery including an engine and ECU31 is the same as that of 1st Embodiment, a component is demonstrated using the code | symbol of 1st Embodiment.

  When the ignition switch is turned on, the ECU 31 is activated, and the intake cam phase control routine shown in FIG. 6 and the EGR gas DC valve control routine corresponding to FIG. 3 are executed at each set calculation cycle.

  The intake cam phase control routine shown in FIG. 6 executes the same processing as the intake cam phase control routine shown in FIG. 2 of the first embodiment described above until steps S1 to S6.

  That is, it is determined in step S3 that the engine operating region is the partial load knock region, the process proceeds to step S5, the partial load knock region determination flag FG is set (FG ← 1), and the process proceeds to step S21.

  In step S21, a control current value IVT for driving the hydraulic control valve 21 is set as an advance value IVTF that is a valve timing for setting a preset EGR gas DC region (IVT ← IVTF), and step S21 is performed. Proceed to S8. The process in step S21 corresponds to the intake valve timing setting means of the present invention.

  Then, when the process proceeds from step S6 or step S21 to step S8, the control current value IVT is set and the routine is exited.

  The ECU 31 outputs a drive signal corresponding to the control current value IVT to the hydraulic control valve 21 via a drive circuit (not shown).

  The hydraulic control valve 21 outputs a hydraulic pressure corresponding to the control current value IVT to the VVT actuator 19. The VVT actuator 19 varies the phase (displacement angle) of the intake cam 15 in accordance with the hydraulic pressure supplied from the hydraulic control valve 21.

  Then, the valve timing of the intake valve 6 that is opened and closed by the intake cam 15 is varied. That is, when the control current value IVT is set to the advance value IVTF, the valve timing of the intake valve 6 is advanced by a predetermined angle as shown by the broken line in FIG. 7B, and the exhaust valve 7 is opened and closed quickly. Thus, the valve is closed before reaching the intake bottom dead center BDC.

  As a result, as indicated by a broken line in FIG. 5A, the in-cylinder pressure temporarily decreases in a section immediately after the intake valve 6 in the initial intake stroke is closed and immediately after the intake bottom dead center BDC is passed.

  On the other hand, the EGR gas DC valve control routine executed by the ECU 31 performs the same processing as the EGR gas DC valve control routine shown in FIG. 3 of the first embodiment.

  However, in this embodiment, when the engine operation region is in the partial load knock region, the valve timing of the intake valve 6 is advanced to set the valve to open and close quickly, and the valve opening period of the EGR gas DC valve 22 is set. Since the valve closing angle of the intake valve 6 is set to the initial region of the compression bottom dead center BDC, the valve opening angle θOPN read in step S13 is set to the valve closing angle of the intake valve 6, and the valve closing angle read in step S16. θCLS is set to a substantially symmetrical angle across the valve opening angle θOPN and the intake bottom dead center BDC.

  Accordingly, it is determined in step S13 of the routine of FIG. 3 that the cam angle θCAM has reached the valve opening angle θOPN, the process proceeds to step S14, energization of the control current to the EGR coil 23 is started, and the EGR gas DC valve 22 is started. Is opened against the urging force of a valve spring (not shown) (see FIG. 7C). Then, due to the pressure difference between the internal pressure of the combustion chamber 3 at the end of the intake stroke and the internal pressure of the intake passage 8 upstream of the catalyst 14, a part of the exhaust gas passes through the EGR passage 13a and becomes EGR gas from the EGR port 13b as the combustion chamber 3 Supplied in.

  If it is determined in step S16 that the cam angle θCAM has reached the valve closing angle θCLS, in step S17, the power supply to the EGR coil 23 is interrupted, and the EGR gas DC valve 22 is closed by the urging force of the valve spring. (See FIG. 7C), the routine is exited. As a result, the supply of EGR gas to the combustion chamber 3 is shut off.

  Thus, in this embodiment, when the engine operating state is in the partial load knock region, the valve timing of the intake valve 6 is advanced, and the valve closing timing is set before reaching the intake bottom dead center BDC. At the end of the intake stroke, the internal pressure of the combustion chamber 3 temporarily decreases. Since the EGR gas DC valve 22 is opened at that timing, the differential pressure between the internal pressure of the combustion chamber 3 and the intake passage 8 upstream of the catalyst 14 with respect to the combustion chamber 3 at the end of the intake stroke, EGR gas can be supplied instantaneously.

  As a result, the combustion temperature is lowered by the EGR gas, and the occurrence of knocking during the compression stroke can be avoided. Accordingly, the ignition timing can be set relatively to the MBT (Minimum spark advance for Best Torque) side, and even in a high compression ratio engine, the knock limit can be improved and high thermal efficiency can be obtained. Furthermore, since the EGR gas is not directly supplied in a region where knocking is difficult to occur even in the partial load region, stable combustion can be obtained.

  The present invention is not limited to the above-described embodiments. For example, the knock region is not limited to the partial load region, and can be applied to all regions where knock occurs.

  Further, the engine employed in each of the above-described embodiments is provided with a normal EGR control mechanism that supplies EGR gas to the intake passage side. When the engine operation region is a partial load knock region, the EGR gas DC valve Since 22 is opened, the amount of GEGR gas supplied to the combustion chamber 3 is increased.

1 ... Engine body,
3 ... combustion chamber,
6 ... Intake valve,
7 ... Exhaust valve,
8 ... Intake passage,
13 ... exhaust passage,
13a ... EGR passage,
13b ... EGR port,
14 ... Catalyst,
15 ... Intake cam,
19 ... VVT actuator,
22 ... EGR gas DC valve,
23 ... EGR coil,
27 ... Cam angle sensor,
FG: Partial load knock region determination flag,
IVT: Control current value,
IVTF ... advance value,
IVTN: Normal value,
IVTR: retard value,
Ne ... engine speed,
Q ... Intake air volume,
TDC ... Top dead center,
θCAM ... Cam angle
θCLS ... Valve closing angle,
θOPN ... Valve opening angle

Claims (4)

A variable valve timing mechanism that can vary the valve timing of the intake valve;
An EGR passage communicating the exhaust passage and the combustion chamber;
An EGR valve mechanism for opening and closing the EGR passage;
Control means for controlling the operation of the variable valve timing mechanism and the EGR valve mechanism,
The control means includes
Knock region determining means for determining a knock region based on the operating state of the engine;
An intake valve timing setting means for setting a region where the in-cylinder pressure decreases during the intake stroke by displacing the valve timing of the intake valve by the valve timing variable mechanism when the knock region is determined by the knock region determination means;
An engine combustion control device comprising: EGR timing setting means for opening the EGR valve mechanism in a region where the in-cylinder pressure set by the intake valve timing setting means decreases. The intake valve timing setting means opens the intake valve after the intake top dead center and sets a region where the in-cylinder pressure decreases at least between the intake top dead center and the intake valve opening. The engine combustion control apparatus according to claim 1. The intake valve timing setting means closes the intake valve before the intake bottom dead center, and sets a region where the in-cylinder pressure decreases at least between the time when the intake valve is closed and the intake bottom dead center. The engine combustion control apparatus according to claim 1, wherein The EGR passage has an EGR port that opens to the combustion chamber;
The EGR valve mechanism has an EGR valve that opens and closes the EGR port and an electromagnetic coil that opens and closes the EGR valve,
4. The engine combustion control device according to claim 1, wherein the control means energizes the electromagnetic coil to open the EGR valve. 5.

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