JP2011185170A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine, performing HCCI (Homogeneous Charge Compression Ignition) operation as much as possible when releasing a fuel cut. <P>SOLUTION: A valve opening control part 47, when a fuel cut is started during SI (Spark Ignition) operation (cycle 1), fully closes an intake valve 22 and drives an exhaust valve 23 with a small lift to stay EGR gas in a cylinder (cycle 2). Then, the valve opening control part 47 fully closes both intake and exhaust valves 22, 23 to keep the EGR gas remaining in the cylinder (cycles 3-5), and after release of the fuel cut, drives the intake valve 22 with a small lift to introduce fresh air (cycle 6). With this, temperature decrease of the cylinder is suppressed by the heat of the EGR gas, and the EGR gas becoming unnecessary after release of the fuel cut is discharged. Thereafter, the valve opening control part 47 drives the intake and exhaust valves 22, 23 with a small list to start the HCCI operation (cycles 7, 8). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine mounted on an automobile or the like, and more particularly, to a technique for facilitating HCCI operation as much as possible when releasing a fuel cut.

  Development of internal combustion engines that operate with premixed compression ignition (hereinafter referred to as HCCI) combustion (hereinafter referred to as HCCI operation) in order to improve thermal efficiency and reduce harmful exhaust gas components in recent years (See Patent Document 1). In the HCCI engine, a premixed gas, which is a homogeneous mixture of gasoline, DME (dimethyl ether), n-butane, etc., and air is introduced into the combustion chamber, and then compressed by a piston to achieve high temperature and high pressure simultaneously. The pre-mixed gas is self-ignited, but the load range (establishment range) in which HCCI combustion is established is limited, so when the operation request is outside this load range (that is, the operation request is higher than the establishment range) In the case of a low load side), it is common to switch from HCCI operation to operation by spark ignition (hereinafter referred to as SI) combustion (hereinafter referred to as SI operation).

  On the other hand, a hybrid vehicle has appeared in which an internal combustion engine and a motor generator are arranged side by side, and at least one of the internal combustion engine and the motor generator is used as a driving power source in accordance with the driving situation of the automobile and the driver's acceleration / deceleration request. (See Patent Document 2). Hybrid vehicles have high acceleration performance and climbing ability by using an internal combustion engine and a motor generator at the same time, and use only a motor generator to reduce fuel consumption and achieve quietness during night driving. There are various features such as being able to be recovered as electric energy by a motor generator.

Japanese Patent No. 3936901 JP 2009-292287 A

  In automobiles, fuel supply is interrupted (fuel) in order to reduce fuel consumption (ie, improve fuel efficiency) and improve quietness when idling stops or when decelerating when stopped due to a red light or traffic jam. In general, the internal combustion engine is stopped by executing (Cut). The fuel cut is stopped by the driver depressing the accelerator pedal or the operating state of the engine, and fuel supply is started when the internal combustion engine is restarted. When fuel cut is performed with the above-described HCCI engine, it is desirable to perform HCCI operation when the internal combustion engine is restarted in order to improve fuel efficiency. However, the temperature in the cylinder (in-cylinder temperature) is reduced while the internal combustion engine is stopped. The HCCI operation may not be performed due to a decrease.

Therefore, in Patent Document 1, when returning from the fuel cut, the SI operation is performed over a period corresponding to the continuous length of the fuel cut even under a load condition for performing the HCCI operation. However, when the SI operation is simply performed based on the fuel cut duration, the HCCI operation is less likely to be performed when returning from the fuel cut, and O ₂ and NOx in the exhaust purification catalyst are removed. Therefore, there is a problem that the fuel consumption is deteriorated because it is necessary to enrich the fuel in order to achieve this, and the SI operation is lower in thermal efficiency than the HCCI operation.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a control device for an internal combustion engine that performs HCCI operation as much as possible when fuel cut is canceled.

  A first aspect of the present invention is a control device for controlling an internal combustion engine that can select between HCCI operation by premixed compression ignition combustion and SI operation by spark ignition combustion, and the operation of the internal combustion engine at the start of fuel cut. HCCI availability determination means for determining whether or not the internal combustion engine can be operated in HCCI when the fuel cut is released according to the state, and when the determination result of the HCCI availability determination means is affirmative, It is characterized by operating the engine in HCCI.

  Further, the second aspect of the present invention further includes a valve opening characteristic varying means capable of changing at least the valve opening characteristic of the exhaust valve, and when the determination result of the HCCI availability determination means is affirmative, In order to leave a large amount of internal EGR gas, the timing for closing the exhaust valve during the exhaust stroke of the combustion cycle for performing fuel cut is advanced.

  The third aspect of the present invention is characterized in that at least one of the intake valve and the exhaust valve is deactivated in a cylinder in which a large amount of internal EGR gas remains.

  According to a fourth aspect of the present invention, when the determination result of the HCCI availability determination means is negative, the intake valve and the exhaust valve are deactivated during the fuel cut to scavenge the EGR gas in the cylinder. It is characterized by that.

  Further, according to a fifth aspect of the present invention, an HCCI in which an HCCI possible period in which the internal combustion engine can be operated in HCCI when the fuel cut is released is set based on the fuel cut start time according to the operating state of the internal combustion engine at the fuel cut start time. Period setting means is further provided, and the internal combustion engine is HCCI-operated from when the fuel cut is canceled if the fuel cut duration is within the HCCI possible period.

  Further, the sixth aspect of the present invention further includes in-cylinder temperature estimating means for estimating an in-cylinder temperature of the internal combustion engine, and if the in-cylinder temperature is within a predetermined HCCI possible temperature range, The internal combustion engine is HCCI-operated at the time of return.

  According to the first aspect of the present invention, an increase in the rate at which the HCCI operation is performed when the fuel cut is canceled increases the thermal efficiency, reduces harmful exhaust gas components, and the like. Further, according to the second aspect of the present invention, the drop in the in-cylinder temperature is moderated by the remaining EGR gas, and the rate at which the HCCI operation is performed when the fuel cut is released is further increased. In addition, according to the third aspect of the present invention, the EGR gas remaining in the cylinder can be maintained at a high temperature, so that the ratio of performing the HCCI operation when the fuel cut is released is further increased. Further, according to the fourth aspect of the present invention, the EGR gas in the cylinder is scavenged before the fuel cut is released, and the SI operation is facilitated. According to the fifth aspect of the present invention, if the fuel cut duration is relatively short, the HCCI operation is performed when the fuel cut is released. According to the sixth aspect of the present invention, if the estimation result of the in-cylinder temperature is relatively high, the HCCI operation is performed when the fuel cut is released.

It is a schematic block diagram of the power unit which concerns on embodiment. It is a schematic block diagram of PCU which concerns on embodiment. It is a flowchart which shows the procedure of the combustion mode determination which concerns on embodiment. It is a graph which shows a time-dependent change of the fuel cut counter which concerns on embodiment. It is a graph which shows a time-dependent change of the fuel cut counter which concerns on embodiment. It is a flowchart which shows the procedure of valve opening control which concerns on embodiment. It is a term chart which shows the flow of the 1st valve opening mode which concerns on embodiment. It is a term chart which shows the flow of the 2nd valve opening mode which concerns on embodiment. It is a term chart which shows the flow of the 3rd valve opening mode which concerns on embodiment. It is a term chart which shows the flow of the 4th valve opening mode which concerns on embodiment. It is a term chart which shows the flow of the 5th valve opening mode which concerns on embodiment. It is an HCCI operable load region map according to the embodiment.

  Hereinafter, an embodiment in which the present invention is applied to power unit control of an automobile (hybrid vehicle) will be described in detail with reference to the drawings.

<< Configuration of Embodiment >>
<Schematic configuration of power unit>
As shown in FIG. 1, the power unit 1 according to this embodiment includes an engine 2 and a motor generator 3, and applies driving force to left and right front wheels (not shown) via a transmission 4 integrated with a differential device.

  The engine 2 is an inline 4-cylinder HCCI engine, and includes an intake system including an air cleaner 11, an electric throttle valve 12, a surge tank 13, an intake pipe 14, and the like, an exhaust manifold 15, an exhaust purification catalyst 16, an exhaust pipe 17, and the like. It has an exhaust system. The cylinder head 21 of the engine 2 includes a variable valve mechanism 26 that changes the valve opening characteristics of a pair of intake valves 22, a pair of exhaust valves 23, a spark plug 25, and intake and exhaust valves 22, 23 for each cylinder. 27 etc. are provided. The intake pipe 14 is provided with a fuel injection valve 28 for each cylinder. The variable valve mechanisms 26 and 27 of the present embodiment have three types with different cam phases and lift amounts so as to switch the valve opening characteristics of the intake and exhaust valves 22 and 23 in three stages (pause, small open, and large open), respectively. Has a cam.

  The motor generator 3 includes a motor 31 that is used for driving force assist for the engine 2 and electric running, and a generator 32 that converts the output of the engine 2 and the running energy of the automobile into electric power. A transmission and a differential device (not shown) are provided. Via the left and right front wheels. The motor generator 3 is connected to a battery 33 mounted at the rear of the vehicle body of the automobile, and exchanges power with the battery 33. A downverter 34 composed of a DC-DC converter or the like is connected to the battery 33, and the electric power that has been stepped down to 12V by the downverter 34 is used in various electric auxiliary machines (such as an electric air conditioner and an electric water pump) and an electric device. (Lights, electric heaters, etc.)

  A PCU (power control unit) 41 is mounted on the body of the automobile, and the PCU 41 controls the engine 2 and the motor generator 3 in an integrated manner. In addition to information from the engine 2, the motor generator 3, the battery 33, and the like, the PCU 41 receives information on the amount of depression of the accelerator pedal 43 from the accelerator sensor 42 (that is, the driver's requested engine output).

<Schematic configuration of PCU>
As shown in FIG. 2, the PCU 41 is a fuel cut control unit 45 that determines whether or not fuel cut is possible for the engine 2 based on the vehicle speed and the like, and combustion that determines the combustion mode of the engine 2 based on the engine speed, the target engine load, and the like. A mode determination unit 46 and a valve opening control unit 47 that performs valve opening control of the intake and exhaust valves 22 and 23 based on the determination result of the combustion mode determination unit 46 and the like are provided.

<< Operation of Embodiment >>
When the fuel cut is performed during idling stop or deceleration, the fuel cut control unit 45 starts the fuel cut for the engine 2 and simultaneously sets the fuel cut flag Ffc to 1 in the combustion mode determination unit 46 and the valve opening control unit 47. Output. The value of the fuel cut flag Ffc is 1 when the fuel cut is being executed, and is 0 when the fuel cut is not being executed.

<Combustion mode judgment>
When the fuel cut flag Ffc input from the fuel cut control unit 45 becomes 1, the combustion mode determination unit 46 performs the combustion mode determination control whose procedure is shown in the flowchart of FIG. 3 at a predetermined control interval (for example, 10 msec). Start running with. When the combustion mode determination control is started, the combustion mode determination unit 46 determines whether or not the fuel cut flag Ffc is 1 in step S1 of FIG. 3, and the first determination is naturally Yes, so in step S2 It is determined whether or not the fuel cut counter Cfc of the initial value N is zero. The fuel cut counter Cfc is a counter for determining whether or not the HCCI operation can be performed when the fuel cut is released. When the value becomes 0 (that is, when a predetermined time elapses), the cylinder temperature decreases. Thus, the SI operation is selected when the engine 2 is restarted. Here, the initial value N is a natural number having a relatively large value.

  Immediately after the start of fuel cut, the determination in step S2 is No. Therefore, after setting the HCCI standby flag Fhstb to 1 in step S3, the combustion mode determination unit 46 decrements the fuel cut counter Cfc by 1 in step S4. If the fuel cut is canceled before the fuel cut counter Cfc becomes 0, the HCCI standby flag Fhstb is set to 1 at the time when the fuel cut is canceled (FIG. 4). Further, when the fuel cut is continuously performed for a predetermined time and the fuel cut counter Cfc becomes 0, the combustion mode determination unit 46 sets the HCCI standby flag Fhstb to 0 in step S5 (FIG. 5).

  When the driver depresses the accelerator pedal 43 to restart the vehicle, the fuel cut control unit 45 releases the fuel cut and simultaneously outputs a fuel cut flag Ffc having a value of 0 to the combustion mode determination unit 46. Then, since determination of step S1 is No, the combustion mode determination part 46 determines whether HCCI environmental conditions are satisfied by step S6. If this determination is No, the combustion mode determination unit 46 sets the fuel cut counter Cfc to 0 in step S7, sets the HCCI standby flag Fhstb to 0 in step S8, and sets the HCCI permission flag Fhcci to 0 in step S9. . The establishment of the HCCI environmental condition is determined from a map or an arithmetic expression (not shown) based on the intake air temperature, the coolant temperature, the intake air pressure, and the like.

  On the other hand, when the HCCI environmental condition is satisfied and the determination in step S6 is Yes, the combustion mode determination unit 46 in step S10 obtains the fuel cut counter Cfc (CFCHCCI) obtained by multiplying the engine speed NE by the engine load LE. ) To search the CFCHCCI map. Next, the combustion mode determination unit 46 determines whether or not the fuel cut counter Cfc is 0 in step S11. If this determination is Yes, the combustion mode determination unit 46 sets the HCCI standby flag Fhstb to 0 in step S12. In step S13, the HCCI standby flag Fhstb is set to 1.

  Next, the combustion mode determination unit 46 determines whether or not the previous value Ffcz of the fuel cut flag Ffc was 1 in step S14. If the determination in step S14 is Yes (that is, immediately after canceling the fuel cut), the combustion mode determination unit 46 determines whether or not the value of the HCCI standby flag Fhstb is 1 in step S15. If Yes, the HCCI permission flag Fhcci is set to 1 in step S16, and if No, the HCCI permission flag Fhcci is set to 0 in step S17.

  When the previous value Ffcz of the fuel cut flag Ffc is 0 and the determination in step S14 is No, the combustion mode determination unit 46 determines whether or not the HCCI permission condition is satisfied in step S18. And if the determination of step S18 is Yes, the combustion mode determination part 46 will transfer to step S16, and will set the HCCI permission flag Fhcci to 1, if it is No, it will transfer to step S9 and set the HCCI permission flag Fhcci to 0. . The establishment of the HCCI permission condition is determined from the engine speed NE and the engine load EL using the HCCI operable load region map of FIG.

<Valve opening control>
When the fuel cut flag Ffc input from the fuel cut control unit 45 becomes 1, the valve opening control unit 47 performs valve opening control whose procedure is shown in the flowchart of FIG. 6 at a predetermined control interval (for example, 10 msec). Start running. When the valve opening control is started, the valve opening control unit 47 determines whether or not the fuel cut flag Ffc is 1 in step S21 of FIG. 6, and the first determination is naturally Yes, so that the HCCI is determined in step S22. It is determined whether or not the standby flag Fhstb is 0. Since the first determination in step S22 is No when the HCCI standby flag Fhstb is 1 in the combustion mode determination described above, the valve opening control unit 47 returns to the start without performing any processing.

  When the driver depresses the accelerator pedal 43 to restart the vehicle, the fuel cut control unit 45 releases the fuel cut and simultaneously outputs a fuel cut flag Ffc having a value of 0 to the valve opening control unit 47. Then, since the determination in step S21 is No, the valve opening control unit 47 determines whether or not the fuel cut flag condition (F_FC condition) is established only once in step S23. Return to the start without any processing. The establishment of the F_FC condition is determined by the engine speed NE, the accelerator pedal depression amount, etc. during deceleration fuel cut, and the vehicle speed, accelerator pedal depression amount, braking amount, air conditioner load, battery charge state, etc. during idle stop Is determined by

  When the fuel cut flag condition is established only once and the determination in step S23 is Yes, the valve opening control unit 47 determines whether or not the HCCI standby flag Fhstb is 1 in step S24. If the determination is Yes (that is, a situation in which HCCI operation is possible after canceling the fuel cut), it is determined whether or not the HCCI permission flag Fhcci is 0 in step S25. If this determination is Yes, the valve opening control unit 47 drives and controls the intake / exhaust valves in the first valve opening mode in step S26.

(First valve opening mode)
As shown in FIG. 7, when fuel cut is started during SI operation (cycle 1), the valve opening control unit 47 drives the exhaust valve 23 with a small lift while closing the intake valve 22 fully. EGR gas is kept in the cylinder (cycle 2). Next, the valve opening control unit 47 fully closes both the intake and exhaust valves 22 and 23 to leave the EGR gas in the cylinder (cycles 3 to 5), and drives the intake valve 22 with a small lift after canceling the fuel cut. To introduce fresh air (cycle 6). Thereby, the temperature drop of the cylinder is suppressed by the heat of the EGR gas, and the EGR gas which becomes unnecessary after the fuel cut is released is discharged. Thereafter, the valve opening control unit 47 drives the start intake and exhaust valves 22 and 23 with a small lift to start the HCCI operation (cycles 7 and 8).

  When the HCCI permission flag Fhcci is 1 and the determination in step S25 is No, the valve opening control unit 47 drives and controls the intake / exhaust valves in the second valve opening mode in step S27.

(Second valve opening mode)
As shown in FIG. 8, when the fuel cut is started during the HCCI operation (cycle 1), the valve opening control unit 47 drives the exhaust valve 23 with a small lift while fully closing the intake valve 22. EGR gas is kept in the cylinder (cycle 2). Next, the valve opening control unit 47 fully closes both the intake and exhaust valves 22 and 23 to leave the EGR gas in the cylinder (cycles 3 to 5), and drives the intake valve 22 with a small lift after canceling the fuel cut. To introduce fresh air (cycle 6). Thereby, the temperature drop of the cylinder is suppressed by the heat of the EGR gas, and the EGR gas which becomes unnecessary after the fuel cut is released is discharged. Thereafter, the valve opening control unit 47 drives the start intake and exhaust valves 22 and 23 with a small lift to start the HCCI operation (cycles 7 and 8).

  On the other hand, when the HCCI standby flag Fhstb is 0 and the determination in step S24 is No, the valve opening control unit 47 determines whether or not the HCCI permission flag Fhcci is 0 in step S28. If this determination is Yes, the valve opening control unit 47 drives and controls the intake / exhaust valves in the third valve opening mode in step S29.

(Third valve opening mode)
As shown in FIG. 9, when the fuel cut is started during SI operation (cycle 1), the valve opening control unit 47 drives the exhaust valve 23 with a large lift while fully closing the intake valve 22. EGR gas (exhaust gas) is discharged out of the cylinder (cycle 2). Next, the valve opening control unit 47 fully closes both the intake and exhaust valves 22 and 23 (cycles 3 to 5), and after releasing the fuel cut, drives the intake valve 22 with a large lift to introduce fresh air (cycle 6). ). Thereafter, the valve opening control unit 47 drives the start intake / exhaust valves 22 and 23 with a large lift to start the SI operation (cycles 7 and 8).

When the HCCI permission flag Fhcci is 1 and the determination in step S28 is No, the valve opening control unit 47 drives and controls the intake and exhaust valves in the fourth valve opening mode in step S30.
(4th valve opening mode)
As shown in FIG. 10, when the fuel cut is started during the HCCI operation (cycle 1), the valve opening control unit 47 drives the exhaust valve 23 with a small lift while fully closing the intake valve 22. EGR gas is kept in the cylinder (cycle 2). Next, the valve opening control unit 47 drives the exhaust valve 23 with a large lift to discharge EGR gas (exhaust gas) out of the cylinder (cycle 3), and fully closes both the intake and exhaust valves 22 and 23 (cycle). 4, 5). Next, the valve opening control unit 47 drives the intake valve 22 with a large lift after releasing the fuel cut to introduce fresh air (cycle 6), and opens the intake and exhaust valves 22, 23 with a large lift to start SI operation. Drive (cycles 7 and 8).

  When the HCCI standby flag Fhstb is 0 and the determination in step S22 is Yes, the valve opening control unit 47 determines whether or not the previous value Fhstbz of the HCCI standby flag Fhstb is 1 in step S31. If No (that is, if the value of the HCCI standby flag Fhstb has not changed), the process returns to the start without performing any processing.

When the previous value Fhstbz is 1 and the determination in step S31 is Yes, the valve opening control unit 47 drives and controls the intake and exhaust valves in the fifth valve opening mode in step S32.
(5th valve opening mode)
As shown in FIG. 11, when the fuel cut is started during the SI operation (cycle 1), the valve opening control unit 47 drives the exhaust valve 23 with a small lift while fully closing the intake valve 22. The EGR gas is kept in the cylinder (cycle 2), and both the intake and exhaust valves 22 and 23 are fully closed to leave the EGR gas in the cylinder (cycles 3 and 4). Next, the valve opening control unit 47 drives the exhaust valve 23 with a large lift to discharge the EGR gas out of the cylinder (cycle 5), and fully closes both the intake and exhaust valves 22 and 23 again (cycle 6). Next, the valve opening control unit 47 drives the intake valve 22 with a large lift after releasing the fuel cut to introduce fresh air (cycle 7), and opens the intake and exhaust valves 22, 23 with a large lift to start SI operation. Drive (cycle 8).

  In the present embodiment, by adopting the above-described configuration, the ratio at which the HCCI operation is performed after the fuel cut becomes higher than that of the conventional device, and it is possible to realize improvement in thermal efficiency, reduction in harmful exhaust gas components, and the like.

  Although the description of the specific embodiments is finished as described above, the present invention is not limited to these embodiments and can be widely modified. For example, the above-described embodiment is an application of the present invention to an HCCI engine mounted on a hybrid vehicle, but it is naturally applicable to an HCCI engine mounted on a normal vehicle. In addition, the specific configuration of the power unit, the specific procedure of the control, and the like can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Power unit 2 Engine 22 Intake valve 23 Exhaust valve 26, 27 Variable valve mechanism (Valve opening characteristic variable means)
41 PCU
45 Fuel Cut Control Unit 46 Combustion Mode Determination Unit 47 Valve Opening Control Unit

Claims (6)

A control device for controlling an internal combustion engine capable of selecting HCCI operation by premixed compression ignition combustion and SI operation by spark ignition combustion,
HCCI availability determination means for determining whether or not the internal combustion engine can be operated in HCCI when the fuel cut is released according to the operating state of the internal combustion engine at the start of fuel cut;
A control apparatus for an internal combustion engine, wherein when the determination result of the HCCI availability determination means is affirmative, the internal combustion engine is HCCI-operated from when the fuel cut is released. It further comprises valve opening characteristic variable means capable of changing at least the valve opening characteristic of the exhaust valve,
When the determination result of the HCCI availability determination means is affirmative, the timing for closing the exhaust valve during the exhaust stroke of the combustion cycle for performing fuel cut is advanced so that a large amount of internal EGR gas remains in the cylinder. The control device for an internal combustion engine according to claim 1.   The control apparatus for an internal combustion engine according to claim 2, wherein at least one of the intake valve and the exhaust valve is deactivated in a cylinder in which a large amount of internal EGR gas remains.   3. The suspension of the intake valve and the exhaust valve is released during fuel cut to scavenge the EGR gas in the cylinder when the determination result of the HCCI availability determination means is negative. Item 4. A control device for an internal combustion engine according to Item 3. HCCI period setting means for setting an HCCI possible period in which the internal combustion engine can be operated in HCCI when the fuel cut is released, starting from the fuel cut start time, according to the operation state of the internal combustion engine at the fuel cut start time,
5. The internal combustion engine according to claim 1, wherein the internal combustion engine is HCCI-operated from when the fuel cut is canceled if the fuel cut duration is within the HCCI possible period. 6. Engine control device. In-cylinder temperature estimating means for estimating the in-cylinder temperature of the internal combustion engine is further provided,
The HCCI operation of the internal combustion engine is performed when returning from a fuel cut if the in-cylinder temperature is within a predetermined HCCI allowable temperature range. Control device for internal combustion engine.

Images