JP2009002279A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand an operation area capable of controlling the suction air volume by an intake valve, in a control device of an internal combustion engine. <P>SOLUTION: An operation characteristic of the intake valve is variably controlled based on request torque and an EGR quantity so that new gas of quantity required for realizing the request torque is sucked in a cylinder. The EGR quantity is increased more than the other operation area in a low load area for reducing a requiring quantity of the new gas. <P>COPYRIGHT: (C)2009,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 capable of controlling an intake air amount into a cylinder by an intake valve.

A variable valve mechanism that makes the working angle and maximum lift of the intake valve variable is known. Each patent document listed below discloses a technique for controlling the amount of intake air into a cylinder by changing the operating characteristics of the intake valve by a variable valve mechanism. The control of the intake air amount using the intake valve is superior in controllability to the extent that there is no delay due to the intake volume compared to the control of the intake air amount using the throttle.
JP 2004-197566 A JP 2004-324428 A JP 2004-1000064 A

  In the valve operating system that drives the intake valve, there are variations in the machining accuracy and assembly accuracy of the parts for each cylinder. For this reason, the operation characteristics such as the operating angle and the maximum lift amount are not always the same between the cylinders. When there is a variation in the operating characteristics of the intake valves among the cylinders, the influence becomes relatively large during low load operation with a small intake air amount. That is, during low load operation, the amount of error due to variations in operating characteristics increases as the amount of intake air decreases, resulting in large variations in the intake air amount ratio between cylinders.

  Thus, in reality, there is a lower limit on control accuracy in the amount of intake air that can be controlled by the intake valve. If the intake air amount is to be controlled even below the lower limit, it is necessary to switch to intake air amount control by the throttle while fixing the operating characteristics of the intake valve, as disclosed in, for example, Patent Document 3 above. .

  However, as described above, the intake air amount control by the intake valve has an advantage that cannot be obtained by the throttle. For this reason, there has been a demand for enabling the intake air amount control by the intake valve in the entire region including the low load region.

  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 in which the operating range in which the intake air amount can be controlled by an intake valve is expanded.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
An intake valve provided at a connection portion between the intake pipe and the cylinder, the operation characteristics of which can be changed by a variable valve mechanism;
An intake control means for variably controlling the operation characteristics of the intake valve based on the required torque and the EGR amount so that a new gas in an amount necessary for realizing the required torque is sucked into the cylinder;
EGR control means for increasing the EGR amount in the low load range where the required amount of new gas is reduced compared to other operating ranges;
It is characterized by having.

According to a second invention, in the first invention,
The EGR control means includes means for changing an overlap period of the intake valve and the exhaust valve, and increases an exhaust gas blowback amount from the exhaust pipe to the intake pipe by increasing the overlap period. It is characterized by.

According to a third invention, in the first invention,
The EGR control means includes means for changing the valve timing of the exhaust valve, and the residual gas amount in the cylinder is increased by making the closing timing of the exhaust valve earlier than the top dead center.

According to a fourth invention, in the first invention,
The EGR control means includes an EGR valve provided between the intake pipe and the exhaust pipe, and recirculates exhaust gas from the exhaust pipe to the intake pipe by increasing the opening of the EGR valve. It is characterized by increasing the amount.

A fifth invention is the fourth invention,
The intake control means is characterized in that the opening timing of the intake valve is delayed until the latter half of the intake stroke in the low load range.

A sixth invention is any one of the first to fifth inventions,
A plurality of the intake valves are provided in one cylinder,
The intake control means is characterized in that, in the low load range, a part of the plurality of intake valves is stopped by being fully closed.

  According to the first aspect of the invention, in the low load range where the required amount of new gas is reduced, the EGR amount is increased instead, thereby reducing the apparent intake air amount. If the apparent amount of intake air can be secured, the effects of variations in the intake valve operating characteristics among cylinders can be reduced, so accurate intake by the intake valve can be achieved even in low load areas where the required amount of new gas is reduced. Air volume control becomes possible.

  According to the second invention, by increasing the overlap period of the intake valve and the exhaust valve, it is possible to increase the amount of exhaust gas blown back from the exhaust pipe to the intake pipe, thereby increasing the so-called internal EGR amount. .

  According to the third invention, the amount of residual gas in the cylinder can be increased by increasing the closing timing of the exhaust valve from the top dead center, thereby increasing the so-called internal EGR amount.

  According to the fourth invention, by increasing the opening degree of the EGR valve, the recirculation amount of the exhaust gas from the exhaust pipe to the intake pipe can be increased, and the so-called external EGR amount can be increased.

  According to the fifth aspect of the invention, when the external EGR is introduced, the intake valve is opened in the latter half of the intake stroke, so that the intake flow velocity when the intake valve is opened can be increased. According to this, the lean limit at the time of EGR introduction can be increased by promoting the atomization of fuel.

  According to the sixth aspect of the present invention, in the low load range, a part of the plurality of intake valves is stopped in a fully closed state, thereby increasing the apparent intake air amount in the remaining operating intake valves. Can do. According to this, the accuracy of intake air amount control in the low load region can be improved.

Embodiment 1 FIG.
[Engine system configuration]
FIG. 1 is a schematic configuration diagram of an engine system provided with a control device for an internal combustion engine as a first embodiment of the present invention. In other embodiments described later, the structure of the engine system is as shown in FIG.

  The engine 2 according to the present embodiment is a spark ignition type four-stroke engine, and has a plurality of cylinders 10 (only one is shown in the figure). An intake pipe 4 and an exhaust pipe 6 are connected to the cylinder 10. An intake valve 12 for controlling the communication state is provided at a connection portion between the cylinder 10 and the intake pipe 4. Further, an exhaust valve 14 for controlling the communication state is provided at a connection portion between the cylinder 10 and the exhaust pipe 6.

  Each of the intake valve 12 and the exhaust valve 14 is provided with variable valve mechanisms 22 and 24 that can change the operation characteristics thereof. The intake side variable valve mechanism 22 is a mechanism that can vary the valve timing, the operating angle, and the maximum lift amount of the intake valve 12. Only one of the operating angle and the maximum lift amount of the intake valve 12 may be variable. The exhaust-side variable valve mechanism 24 is a mechanism that can change at least the valve timing of the exhaust valve 14. There is no limitation regarding the structure of these variable valve mechanisms 22 and 24. In this system, the amount of air taken into the cylinder 10 can be controlled by changing the operating angle and the maximum lift amount of the intake valve 12 by the variable valve mechanism 22 on the intake side. Further, the valve overlap can be controlled by changing the valve timing of at least one of the intake valve 12 and the exhaust valve 14.

  An electronically controlled throttle 20 is disposed upstream of the intake pipe 4. In this system, the amount of air taken into the cylinder 10 can also be controlled by the throttle 20. An intake pipe pressure sensor 32 that outputs a signal corresponding to the internal pressure (intake pipe pressure) is attached to the intake pipe 4.

  The exhaust pipe 6 and the intake pipe 4 are connected by an EGR pipe 16. A connection portion of the EGR pipe 16 in the intake pipe 4, that is, an exhaust gas introduction section is located downstream of the throttle 20, specifically, a surge tank. The EGR pipe 16 is provided with an EGR valve 26 for adjusting the exhaust gas recirculation amount.

  In addition to the intake pipe pressure sensor 32, the system is provided with a plurality of sensors such as an accelerator opening sensor 34 that outputs a signal corresponding to the accelerator opening. Signals from the sensors 32 and 34 are input to an ECU (Electronic Control Unit) 30 that comprehensively controls the entire system. The ECU 30 determines the control amounts of the variable valve mechanisms 22, 24, the throttle 20, and the EGR valve 26 based on signals emitted from the sensors 32, 34 and other various information. The engine 2 is provided with various actuators such as an injector and an ignition device in addition to the variable valve mechanisms 22 and 24, the throttle 20 and the EGR valve 26. However, since they are not related to the main part of the present invention, the display in the figure and the description in the present specification are omitted.

[Characteristics of intake air amount control according to Embodiment 1]
As described above, the system of the present embodiment includes the intake valve 12 with the variable valve mechanism 22 and the throttle 20 as means for controlling the amount of intake air into the cylinder 10. By cooperatively controlling the intake valve 12 and the throttle 20, the intake air amount into the cylinder 10 can be controlled to the intake air amount corresponding to the required torque.

  The intake air amount control performed by the ECU 30 in the present embodiment is characterized in that the intake air amount control mainly using the intake valve 12 is performed in substantially the entire region including the low load region. That is, the throttle 20 is set to an opening that does not control the intake air amount, and the variable valve mechanism 22 changes the operation characteristics of the intake valve 12 to control the intake air amount into the cylinder 10. Below, the detail of the intake air amount control implemented by ECU30 is demonstrated using FIG.2 and FIG.3.

  The flowchart of FIG. 2 shows a routine for selecting the specifications of the valve system and driving the valve system based on it. The valve system here refers to the entire system including not only the intake side variable valve mechanism 22 and the intake valve 12 but also the exhaust side variable valve mechanism 24 and the exhaust valve 14. Further, the specifications of the valve operating system selected here include the valve timing of the intake valve 12, the operating angle and the maximum lift amount, and the valve timing of the exhaust valve 14. The ECU 30 repeatedly executes the routine shown in FIG. 2 at a predetermined execution timing.

  In the first step S100 of the routine shown in FIG. 2, an optimal valve operating map is selected as a map for associating the required torque with the valve operating system specifications. There are a plurality of valve system specifications for realizing the required torque, but the valve system specifications are set so that the fuel efficiency is optimized in the optimal valve map. In the optimum valve operating map used in the present embodiment, a valve overlap amount is used in addition to the required torque as a parameter used for determining the valve operating system specifications. If the valve overlap amount, that is, the setting of the overlap period of the intake valve 12 and the exhaust valve 14 changes, the amount of exhaust gas blow-back from the exhaust pipe 6 to the intake pipe 4 changes, and eventually into the cylinder 10. This is because a change occurs in the EGR amount in the intake air amount.

  In the next step S102, the intake pipe pressure Pim measured by the intake pipe pressure sensor 32 is compared with a preset reference pressure Pimlb (step S120). Although the intake pipe pressure Pim varies depending on the throttle opening, the setting of the throttle opening in the present embodiment is such that the intake air amount defined by the throttle 20 is slightly smaller than the intake air amount defined by the intake valve 12. It is set to be larger. For this reason, when the operating angle and the maximum lift amount of the intake valve 12 are reduced in order to reduce the intake air amount into the cylinder 10, the throttle opening also decreases accordingly, and as a result, the intake pipe pressure Pim also decreases. It is like that. The reference pressure Pimlb corresponds to the lower limit of the intake air amount that can be accurately controlled by the intake valve 12.

  If the result of the determination in step S102 is that the intake pipe pressure Pim is higher than the reference pressure Pimlb, the valve system parameters are determined using the optimal valve map based on the current valve overlap amount setting value and the required torque. The valve drive system is set based on the valve system specifications (step S106).

  On the other hand, when the intake pipe pressure Pim is lower than the reference pressure Pimlb, the process of step S104 is performed. In step S104, the valve overlap amount setting is changed to a setting larger than normal. Then, based on the set value of the increased valve overlap amount and the required torque, the valve operating system specifications are set using the optimal valve operating map, and based on the valve operating system specifications, the valve system drive processing is performed. Implemented (step S106). FIG. 3 shows an example of each operation of the intake valve (IN) 12 and the exhaust valve (EX) 14 at this time.

[Effect of intake air amount control of Embodiment 1]
According to the routine described above, the internal EGR amount is increased by increasing the valve overlap amount in the low load region where the required amount of new gas decreases. As the internal EGR amount is increased, the air amount (apparent intake air amount) to be sucked into the cylinder 10 in order to secure a necessary amount of new gas is increased accordingly. If the apparent intake air amount can be sufficiently secured, it is possible to reduce the influence of variations in the operating characteristics of the intake valve 12 between the cylinders 10, and the intake valve 12 can be accurately controlled by the intake valve 12. Therefore, according to the present embodiment, it is possible to control the intake air amount mainly using the intake valve 12 over almost the entire region including the low load region.

  2 is implemented by the ECU 30, the “intake control means” of the first invention and the “EGR control means” of the first and second inventions are realized.

Embodiment 2. FIG.
[Characteristics of Intake Air Amount Control of Embodiment 2]
The control device for an internal combustion engine as the second embodiment of the present invention is different from the first embodiment in the content of intake air amount control. The configuration of the engine system is the same as that of the first embodiment, and is shown in FIG. In the following description, regarding the configuration of the engine system, reference is made to FIG. 1 and the reference numerals in FIG. 1 are used. Hereinafter, details of intake air amount control performed by the ECU 30 will be described with reference to FIGS. 4 and 5.

  The flowchart of FIG. 4 shows a routine for selecting the specifications of the valve system and driving the valve system based on it. In the flowchart of FIG. 4, processes that are the same as those in the flowchart of FIG. 2 are assigned common numbers.

  In the first step S100 of the routine shown in FIG. 4, an optimum valve operating map is selected as a map for associating the required torque with the valve operating system specifications. In the optimum valve operating map used in the present embodiment, the closing timing of the exhaust valve 14 is used in addition to the required torque as a parameter used for determining the valve operating system specifications. If the exhaust valve 12 is closed earlier than the top dead center, the exhaust gas remains in the cylinder 10. Therefore, if the setting of the closing timing of the exhaust valve 14 is changed, the residual gas amount in the cylinder 10 is changed, and consequently, the EGR amount in the intake air amount into the cylinder 10 is changed.

  In the next step S102, the intake pipe pressure Pim measured by the intake pipe pressure sensor 32 is compared with the reference pressure Pimlb (step S120). When the intake pipe pressure Pim is higher than the reference pressure Pimlb, the valve system parameters are set using the optimal valve map based on the current setting value of the closing timing of the exhaust valve 14 and the required torque, Based on the valve system specifications, the valve drive system is driven (step S106).

  On the other hand, when the intake pipe pressure Pim is lower than the reference pressure Pimlb, the process of step S120 is performed. In step S120, the closing timing of the exhaust valve 14 is set to an advance side with respect to the top dead center. Then, based on the set value of the advance timing of the exhaust valve 14 and the required torque, the valve operating system specifications are set using the optimal valve operating map, and the valve operating system specifications are set based on the valve operating system specifications. A driving process is performed (step S106). FIG. 5 shows an example of each operation of the intake valve (IN) 12 and the exhaust valve (EX) 14 at this time.

[Effect of intake air amount control of embodiment 2]
According to the routine described above, in the low load range where the required amount of new gas is reduced, the internal EGR amount is increased by the advance timing of the closing timing of the exhaust valve 14, so that the apparent intake air amount can be secured. Thus, the intake air amount can be accurately controlled by the intake valve 12. Therefore, according to the present embodiment, it is possible to control the intake air amount mainly using the intake valve 12 over almost the entire region including the low load region.

  4 is implemented by the ECU 30, the “intake control means” of the first invention and the “EGR control means” of the first and third inventions are realized.

Embodiment 3 FIG.
[Characteristics of Intake Air Volume Control of Embodiment 3]
The control device for an internal combustion engine as the third embodiment of the present invention differs from the first embodiment in the content of intake air amount control. The configuration of the engine system is the same as that of the first embodiment, and is shown in FIG. However, in the present embodiment, it is assumed that a plurality of intake valves 12 are provided in one cylinder, and a variable valve mechanism 22 is provided in each of them. In the following description, regarding the configuration of the engine system, reference is made to FIG. 1 and the reference numerals in FIG. 1 are used. Hereinafter, details of intake air amount control performed by the ECU 30 will be described with reference to FIG. 6.

  The flowchart of FIG. 6 shows a routine for selecting the specifications of the valve system and driving the valve system based on it. In the flowchart of FIG. 6, the processes common to the flowchart of FIG. The description of the contents already described in the flowchart of FIG. 2 is simplified or omitted.

  The difference between the routine shown in FIG. 6 and the routine shown in FIG. 2 is in the next process in which the setting of the valve overlap amount is changed to a setting larger than normal in step S104. In the routine shown in FIG. 6, the process of step S <b> 130 is newly performed to make a reservation for stopping one of the plurality of intake valves 12.

  In the next step S106, the drive of the intake valve 12 reserved for stop is stopped while being fully closed. For the remaining intake valves 12 that are operating, the valve operating system specifications are set using the optimal valve operating map based on the set value of the increased valve overlap amount and the required torque. Based on the specifications, the valve system drive process is performed.

[Effect of intake air amount control of Embodiment 3]
According to the routine described above, by stopping one of the plurality of intake valves 12 in a fully closed state, the amount of air to be taken in by the remaining intake valves 12 that are operating increases. According to this, in combination with the increase in the internal EGR amount due to the increase in the valve overlap amount, the apparent intake air amount in the operating intake valve 12 can be increased, and the intake air amount control by the intake valve 12 can be increased. Can improve the accuracy.

  The ECU 30 executes the routine shown in FIG. 6 to realize the “intake control means” of the first and sixth inventions and the “EGR control means” of the first and second inventions.

Embodiment 4 FIG.
[Characteristics of Intake Air Amount Control of Embodiment 4]
The control device for an internal combustion engine as the fourth embodiment of the present invention differs from the first embodiment in the content of intake air amount control. The configuration of the engine system is the same as that of the first embodiment, and is shown in FIG. In the following description, regarding the configuration of the engine system, reference is made to FIG. 1 and the reference numerals in FIG. 1 are used. Below, the detail of the intake air amount control implemented by ECU30 is demonstrated using FIG.7 and FIG.8.

  The flowchart of FIG. 7 shows a routine for selecting the specifications of the valve system and driving the valve system based on it. In the flowchart of FIG. 7, the processes common to the flowchart of FIG.

  In the first step S100 of the routine shown in FIG. 7, an optimal valve operating map is selected as a map for associating the required torque with the valve operating system specifications. In the optimum valve operating map used in the present embodiment, the opening of the EGR valve 26 is used in addition to the required torque as a parameter used for determining the valve operating system specifications. By opening the EGR valve 26, exhaust gas is introduced from the exhaust pipe 4 to the intake pipe 6. Therefore, if the setting of the opening degree of the EGR valve 26 is changed, the amount of exhaust gas introduced from the exhaust pipe 4 into the intake pipe 6 is changed, and consequently the amount of EGR in the amount of intake air into the cylinder 10 is changed. Because it occurs.

  In the next step S102, the intake pipe pressure Pim measured by the intake pipe pressure sensor 32 is compared with the reference pressure Pimlb (step S120). When the intake pipe pressure Pim is higher than the reference pressure Pimlb, the valve system parameters are set using the optimal valve map based on the current opening degree of the EGR valve 26 and the required torque. Based on the original, the driving operation of the valve train is performed (step S106).

  On the other hand, when the intake pipe pressure Pim is lower than the reference pressure Pimlb, the process of step S140 is performed. In step S140, a request to increase the opening of the EGR valve 26 is output in order to increase the EGR amount (external EGR amount). In the next step S106, the valve operating system parameters are set using the optimal valve operating map based on the increased set value of the opening of the EGR valve 26 and the required torque, and the valve operating system is operated based on the valve operating system specifications. Valve system drive processing is performed.

  In the valve operating system specifications set at this time, the opening timing of the intake valve 12 is set in the latter half of the intake stroke. By opening the intake valve 12 in the latter half of the intake stroke, the intake flow velocity when the intake valve 12 is opened can be increased. According to this, the lean limit when the external EGR is introduced can be increased by promoting the atomization of the fuel. FIG. 8 shows an example of each operation of the intake valve (IN) 12 and the exhaust valve (EX) 14 at this time.

[Effect of intake air amount control of embodiment 4]
According to the routine described above, the EGR valve 26 is opened and the external EGR amount is increased in a low load range where the required amount of new gas is reduced. Therefore, the apparent intake air amount can be secured, and the intake valve can be secured. 12 enables accurate intake air amount control. Therefore, according to the present embodiment, it is possible to control the intake air amount mainly using the intake valve 12 over almost the entire region including the low load region.

  7 is implemented by the ECU 30, the “intake control means” of the first and fifth inventions and the “EGR control means” of the first and fourth inventions are realized.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the control content of the third embodiment, specifically, the technique of stopping a part of the plurality of intake valves 12 in a low load range by being fully closed is the intake air amount control or the second embodiment of the second embodiment. This can be combined with the intake air amount control of No. 3.

1 is a schematic configuration diagram of an engine system including a control device for an internal combustion engine as an embodiment of the present invention. It is a flowchart which shows the routine for control of the valve operating system implemented in Embodiment 1 of this invention. FIG. 3 is a diagram showing each operation of an intake valve and an exhaust valve in a low load range realized by the routine shown in FIG. 2. It is a flowchart which shows the routine for control of the valve operating system implemented in Embodiment 2 of this invention. FIG. 5 is a diagram showing each operation of an intake valve and an exhaust valve in a low load range realized by the routine shown in FIG. 4. It is a flowchart which shows the routine for control of the valve operating system implemented in Embodiment 3 of this invention. It is a flowchart which shows the routine for control of the valve operating system implemented in Embodiment 4 of this invention. It is a figure which shows each operation | movement of the intake valve and exhaust valve in the low load area | region implement | achieved by the routine shown in FIG.

Explanation of symbols

2 Engine body 4 Intake pipe 6 Exhaust pipe 10 Combustion chamber 12 Intake valve 14 Exhaust valve 16 EGR pipe 20 Throttle 22 Intake side variable valve mechanism 24 Exhaust side variable valve mechanism 26 EGR valve 30 ECU
32 Intake pipe pressure sensor 34 Accelerator opening sensor

Claims (6)

An intake valve provided at a connection portion between the intake pipe and the cylinder, the operation characteristics of which can be changed by a variable valve mechanism;
An intake control means for variably controlling the operation characteristics of the intake valve based on the required torque and the EGR amount so that a new gas in an amount necessary for realizing the required torque is sucked into the cylinder;
EGR control means for increasing the EGR amount in the low load range where the required amount of new gas is reduced compared to other operating ranges;
A control device for an internal combustion engine, comprising:   The EGR control means includes means for changing an overlap period of the intake valve and the exhaust valve, and increases an amount of exhaust gas blown back from the exhaust pipe to the intake pipe by increasing the overlap period. The control device for an internal combustion engine according to claim 1.   The EGR control means includes means for changing a valve timing of an exhaust valve, and increases the residual gas amount in the cylinder by advancing the closing timing of the exhaust valve earlier than the top dead center. The control apparatus for an internal combustion engine according to claim 1.   The EGR control means includes an EGR valve provided between the intake pipe and the exhaust pipe, and recirculates exhaust gas from the exhaust pipe to the intake pipe by increasing the opening of the EGR valve. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the amount is increased.   5. The control apparatus for an internal combustion engine according to claim 4, wherein the intake control means delays the opening timing of the intake valve until the latter half of the intake stroke in the low load region. A plurality of the intake valves are provided in one cylinder,
6. The internal combustion engine according to claim 1, wherein the intake control unit stops a part of the plurality of intake valves when the load is low. Control device.

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