Control apparatus and control method for internal combustion engine

A plurality of intake air amount control devices for controlling an amount of air drawn into a combustion chamber in association with a depression stroke of an accelerator pedal are provided. Each of the intake air amount control devices responds to a change in depression stroke of the accelerator pedal after the lapse of a predetermined delay period.

The disclosure of Japanese Patent Applications No.2002-292493 filed on Oct. 4, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control apparatus for an internal combustion engine and a control method for an internal combustion engine.

2. Description of the Related Art

A control apparatus for controlling operation of an electronic throttle valve for controlling an amount of air drawn into a combustion chamber of an internal combustion engine (intake air amount) is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-89140. In this control apparatus, opening of the electronic throttle valve is controlled in accordance with depression stroke of an accelerator pedal (accelerator depression stroke). For instance, if a required torque increases as a result of an increase in accelerator depression stroke, an amount of intake air is increased by increasing an opening of the electronic throttle valve, while an amount of fuel injected from a fuel injection valve (fuel injection amount) is increased as well. Thus, the required torque is output from the internal combustion engine.

Fuel is injected from the fuel injection valve for a relatively short period after closure of an intake valve. An intake air amount must be estimated from an opening of the electronic throttle valve long before the intake valve is closed, for example, before the intake valve starts opening, and a fuel injection amount must be determined, on the basis of the intake air amount thus estimated, such that a desired air-fuel ratio is obtained. In this case, therefore, a fuel injection amount is determined before an intake air amount is confirmed.

For example, however, if a fuel injection amount is determined according to the procedure mentioned above when an opening of the electronic throttle continues to be increased as a result of a continuous increase in required torque, an actual intake air amount deviates from an intake air amount estimated at the time of determination of the fuel injection amount. Therefore, a desired air-fuel ratio cannot be obtained.

In Japanese Patent Application Laid-Open No. 10-89140, therefore, an opening of an electronic throttle valve is not immediately increased even after an increase in accelerator depression stroke. Instead, the opening of the electronic throttle valve is increased after the lapse of a certain delay period. The delay period is set such that the electronic throttle valve assumes an opening corresponding to an accelerator depression stroke at the time of determination of a fuel injection amount when an intake valve is closed. A fuel injection amount is determined on the basis of an opening of the electronic throttle valve corresponding to an accelerator depression stroke. This means that a fuel injection amount is determined on the basis of an opening of the electronic throttle valve at the time of closure of the intake valve. Thus, a desired air-fuel ratio is obtained.

Thus, in order to obtain a desired air-fuel ratio during a continuous change in intake air amount, it is necessary to precisely estimate an intake air amount and to determine a fuel injection amount.

SUMMARY OF THE INVENTION

There has been known an internal combustion engine including a unit for controlling intake air amount in addition to an electronic throttle valve. In such an internal combustion engine as well, in order to obtain a desired air-fuel ratio during a continuous change in intake air amount, an intake air amount needs to be estimated precisely. For the purpose of precisely controlling operation of the internal combustion engine as well as the purpose of obtaining a desired air-fuel ratio, it is important to precisely estimate an intake air amount.

It is an object of the invention to precisely estimate an intake air amount in an internal combustion engine having a plurality of devices which control intake air amount.

To achieve the object stated above, there is provided a control apparatus or method for an internal combustion engine in accordance with a first aspect of the invention. According to this apparatus or method, in an internal combustion engine having a plurality of intake air amount control devices which control an amount of air drawn into a combustion chamber in association with a depression stroke of an accelerator pedal, a response of each of the intake air amount control devices is delayed by a delay period with respect to a depression of the accelerator pedal. In the aforementioned first aspect, the delay period may be set such that timings when the intake air amount control devices affect an amount of air drawn into the combustion chamber coincide with one another.

Furthermore, the delay period may be a sum of a control-holding period for each of the intake air amount control devices and a response delay period thereof, and the control-holding period for each of the intake air amount control devices may be set such that delay periods for the intake air amount control devices coincide with one another.

There is also provided a control apparatus or method for an internal combustion engine in accordance with a second aspect of the invention. According to this apparatus or method, in an internal combustion engine having a plurality of intake air amount control devices which control an amount of air drawn into a combustion chamber in association with a depression stroke of an accelerator pedal, control timings of the intake air amount control devices is set such that the control timing of at least one of the intake air amount control devices differs the control timing of at least one other of the intake air amount control devices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, the embodiments of the invention will be described with reference to the drawings.FIG. 1illustrates an internal combustion engine in accordance with one embodiment of the invention. Referring toFIG. 1, reference numerals1,2,3,4,5,6,7,8,9,10,11, and12denote an engine body, a cylinder head, a cylinder block, a piston, a combustion chamber, a fuel injection valve, an intake valve, an intake port, an intake pipe, an exhaust valve, an exhaust port, and an exhaust pipe, respectively. The internal combustion engine illustrated inFIG. 1is a spark-ignition four-cylinder internal combustion engine in which fuel is ignited by an ignition plug (not shown). The internal combustion engine is provided with an electronic control unit (ECU)13, to which a depression stroke sensor15for detecting a depression stroke of an accelerator pedal14is connected.

The intake pipe9is provided with a surge tank16. An electronically controlled throttle valve17for throttling a flow passage of the intake pipe9is formed therein. An increase in opening of the throttle valve17leads to an increase in amount of air drawn into the combustion chamber5(intake air amount). A stepper motor18is connected to the throttle valve17. The throttle valve17is driven by the stepper motor18. The stepper motor18is connected to the ECU13. Operation of the stepper motor18is controlled by the ECU13.

An intake air control valve19for controlling flow of air flowing into the combustion chamber5is disposed in the intake port8. As shown inFIG. 2, the intake port8diverges into two intake port branch pipes8aand8b. The intake air control valve19is disposed in one of the intake port branch pipes8b. The intake air control valve19can be so controlled as to assume either its fully open state or its fully closed state. If the intake air control valve19is fully closed, air flows into the combustion chamber5only via one of the intake port branch pipes8a. Therefore, the air that has flown into the combustion chamber5flows in a swirl. As a matter of course, the amount of intake air that flows into the combustion chamber5when the intake air control valve19is fully open is larger than the amount of intake air that flows into the combustion chamber5when the intake air control valve19is fully closed. A stepper motor20is connected to the intake air control valve19as well. The intake air control valve19is driven by the stepper motor20. The stepper motor20is connected to the ECU13. Operation of the stepper motor20is controlled by the ECU13.

A valve mechanism21for lifting the intake valve7is connected thereto. The valve mechanism21can change a maximum lift amount and a working angle of the intake valve7. That is, the valve mechanism21can lift the intake valve7, for example, along different lift curves INa, INb, and INc illustrated in FIG.3. Namely, the valve mechanism21of the invention can continuously change lift characteristics between the lift curve INa indicating that the maximum lift amount and working angle of the intake valve7assume maximum values and a lift curve indicating that the maximum lift amount and working angle of the intake valve7assume zero. If a maximum lift amount or working angle of the intake valve7is increased, an amount of air drawn into the combustion chamber5(intake air amount) increases.

Referring toFIG. 3, a curve EX represents a lift curve of the exhaust valve10. In the invention, if one lift curve is replaced with another, timings when the intake valve7is opened and closed change as well. The valve mechanism21is connected to the ECU13. Operation of the valve mechanism21is controlled by the ECU13. The valve mechanism21may be designed to change only one of maximum lift amount and working angle. In the following description, therefore, maximum lift amount of the intake valve7, working angle of the intake valve7, or both of them will be referred to as opening amount of the intake valve7.

In the first embodiment, opening of the throttle valve17, operational position of the intake air control valve19, and opening amount of the intake valve7(hereinafter also referred to comprehensively as operational state of the intake air amount control devices) are controlled in association with depression stroke of the accelerator pedal14(hereinafter referred to accelerator depression stroke). More specifically, operational state of the intake air amount control devices is controlled such that an increase in required torque resulting from an increase in accelerator depression stroke leads to an increase in intake air amount.

In the first embodiment, an amount of fuel to be injected from the fuel injection valve6(fuel injection amount) is determined such that the mixture in the combustion chamber5exhibits a target air-fuel ratio, on the basis of an intake air amount at the timing when the intake valve7is closed (hereinafter referred to as an intake air amount at the end of intake). It is to be noted herein that there is a fairly short period between termination of an intake stroke and actual injection of fuel. Therefore, if a fuel injection amount were to be determined after detection of an intake air amount at the end of intake, it would be impossible to determine a fuel injection amount before injection of fuel.

In the first embodiment, therefore, a fuel injection amount is determined long before the intake valve7is closed. A fuel injection amount is determined on the condition that an intake air amount at the end of intake be estimated. If the estimated intake air amount precisely coincides with an actual intake air amount at the end of intake, the mixture in the combustion chamber5exhibits a target air-fuel ratio.

In the first embodiment, as described above, an intake air amount at the end of intake is estimated in determining a fuel injection amount. Accordingly, it is necessary to precisely estimate an intake air amount at the end of intake. If an operational state of each of the intake air amount control devices is changed immediately in response to a change in accelerator depression stroke, it is impossible to precisely foresee an operational state of each of the intake air amount control devices at the end of an intake stroke, in determining a fuel injection amount (hereinafter referred to simply as “in determining an injection amount”). Thus, it is impossible to precisely estimate an intake air amount at the timing of intake.

In the first embodiment, therefore, if an accelerator depression stroke is changed, an operational state of each of the intake air amount control devices is changed after the lapse of a certain delay period. In the first embodiment, a delay period is set such that an operational state of each of the intake air amount control devices at the end of an intake stroke corresponds to an accelerator depression stroke before determining an injection amount. That is, the delay period mentioned herein is set longer than a period ranging from determination of an injection amount to subsequent termination of intake stroke. By thus setting a delay period, it becomes possible to precisely estimate an intake air amount at the end of intake stroke in determining an injection amount, on the basis of an accelerator depression stroke at that moment.

Next, the first embodiment will be described with reference to FIG.4. Referring toFIG. 4, reference symbols Gf, IN, tgf, ti, Dth, Si, and Ai denote a period for calculating (determining) a fuel injection amount, an open period of the intake valve7, a timing when an injection amount is determined, a timing when intake stroke is terminated, an opening of the throttle valve17, an operational state of the intake air control valve19, and an opening amount of the intake valve7, respectively.

In an example illustrated inFIG. 4, an accelerator depression stroke increases at a timing t0. Then, as indicated by chain lines TD, TS, and TA inFIG. 4, a target opening of the throttle valve17and a target opening amount of the intake valve7are increased, and after the lapse of a certain period, a target operational state of the intake air control valve19is switched from its fully closed state to its fully open state. In the first embodiment, at a timing t1when a delay period DP has just elapsed, a command to increase an opening of the throttle valve17, a command to switch an operational state of the intake air control valve19from its fully closed state to its fully open state, and a command to increase an opening amount of the intake valve7are actually issued.

Thus, the opening Dth of the throttle valve17, the operational state Si of the intake air control valve19, and the opening amount Ai of the intake valve7at the timing ti when intake stroke is terminated are equal to a target opening of the throttle valve17, a target operational state of the intake air control valve19, and a target opening amount of the intake valve7before the timing tgf when an injection amount is determined, respectively. Accordingly, at the timing tgf when an injection amount is determined, an intake air amount at the timing ti when intake stroke is terminated can be precisely estimated on the basis of a target opening of the throttle valve17, a target operational state of the intake air control valve19, and a target opening amount of the intake valve7.

FIG. 5illustrates a routine for carrying out fuel injection from the fuel injection valve in accordance with the first embodiment. In the routine illustrated inFIG. 5, first of all in a step10, a target opening TD of the throttle valve17, a target state TS of the intake air control valve19, and a target opening amount TA of the intake valve7are calculated. Then in a step11, an opening Dth of the throttle valve17at the end of intake stroke, a state TS of the intake air control valve19at the end of intake stroke, and an opening amount Ai of the intake valve7at the end of intake stroke are foreseen on the basis of target operational states of the respective intake air amount control devices.

Then in a step12, a fuel injection amount is calculated (determined) on the basis of the operational states of the respective intake air amount control devices at the end of intake stroke. It is determined then in a step13whether or not a crank angle CA corresponds to a fuel injection timing CAq (CA=CAq). If it is determined in the step13that CA≠CAq, the step13is repeated until it is determined that CA=CAq. If it is determined in the step13that CA=CAq, the routine proceeds to a step14where fuel injection from the fuel injection valve6is carried out.

FIG. 6illustrates a routine for controlling commands to be issued to the intake air amount control devices in accordance with the first embodiment. In the routine illustrated inFIG. 6, first of all in a step20, a current target opening TD(n) of the throttle valve17, a current target state TS(n) of the intake air control valve19, and a target opening amount TA(n) of the intake valve7are calculated. Then, the target opening TD(n), the target state TS(n), and the target opening amount TA(n) are stored into a storage unit (not shown) in a step21.

Then in a step22, a target opening TD(n-DP) of the throttle valve17, a target state TS(n-DP) of the intake air control valve19, and a target opening amount TA(n-DP) of the intake valve7at a timing precedent to the present moment by a predetermined period DP are read. Then in a step23, commands to equalize operational states of the respective intake air amount control devices with the target operational states TD(n-DP), TS(n-DP), and TA(n-DP) read in the step22respectively are issued.

That is, according to this routine, while current target operational states of the respective intake air amount control devices are read, operational states of the intake air amount control devices are equalized with target operational states at a timing precedent to the present moment by the predetermined period DP. In other words, according to this routine, operational states of the respective intake air amount control devices are controlled to be equalized with target operational states after the lapse of a delay of a predetermined period.

Next, the second embodiment will be described. Even after receiving commands to change operational states of the intake air amount control devices (the throttle valve17, the intake air control valve19, and the valve mechanism21), they do not actually start changing their operational states unless a certain period elapses. That is, the intake air amount control devices have a delay in response. This inherent response delay period differs among the intake air amount control devices. Accordingly, in order to equalize operational states of the respective intake air amount control devices with target operational states at the end of intake stroke, delay periods before issuance of commands to change operational states of the respective intake air amount control devices must be set intentionally in consideration of the inherent delays in response of the respective intake air amount control devices.

In the second embodiment, therefore, in consideration of response delay periods of the respective intake air amount control devices, periods (control-holding periods) for withholding (awaiting) issuance of commands to change operational states of the respective intake air amount control devices are set such that total delay periods for all the intake air amount control devices coincide with one another. If an accelerator depression stroke changes, a command to change an operational state of each of the intake air amount control devices is issued after the lapse of a corresponding one of the control-holding periods thus set. The control-holding periods are set longer than a period ranging from determination of an injection amount to subsequent termination of intake stroke. Thus, operational states of the respective intake air amount control devices at the end of intake stroke can be estimated precisely. Therefore, an intake air amount at the end of intake stroke can be estimated precisely. The second embodiment will be described with reference to FIG.7.

Referring toFIG. 7, reference symbols Gf, IN, tgf, ti, Cd, Dth, Cs, Si, and Ai denote a period for calculating (determining) a fuel injection amount, an opening period of the intake valve7, a timing when an injection amount is determined, a timing when intake stroke is terminated, a command value for the throttle valve17, an opening of the throttle valve17, a command value for the intake air control valve19, an operational state of the intake air control valve19, a command value for the valve mechanism21, and an opening amount of the intake valve7, respectively.

On the embodiment illustrated inFIG. 7, an accelerator depression stroke increases at a timing t0. Then, as indicated by chain lines TD, TS, and TA inFIG. 7, a target opening of the throttle valve17and a target opening amount of the intake valve7are increased, and after the lapse of a certain period, a target operational state of the intake air control valve19is switched from its fully closed state to its fully open state. In the second embodiment, a command to increase an opening of the throttle valve17is actually issued at a timing t2when a control-holding period DP1has just elapsed. In addition, a command to switch an operational state of the intake air control valve19from its fully closed state to its fully open state is actually issued at a timing t2when a control-holding period DP2has just elapsed. Furthermore, a command to increase an opening amount of the intake valve7is actually issued at a timing t1when a cold-holding period DP3has just elapsed.

Thus, the opening Dth of the throttle valve17, the operational state Si of the intake air control valve19, and the opening amount Ai of the intake valve7, at the timing ti when intake stroke is terminated, are equal to a target opening of the throttle valve17, a target operational state of the intake air control valve19, and a target opening amount of the intake valve7before the timing tgf when an injection amount is determined, respectively. Accordingly, at the timing tgf when an injection amount is determined, an intake air amount at the timing ti when intake stroke is terminated can be precisely estimated on the basis of the target opening of the throttle valve17, the target operational state of the intake air control valve19, and the target opening amount of the intake valve7.

FIGS. 8A,8B, and8C illustrate routines for controlling commands to be issued to the intake air amount control devices in accordance with the second embodiment.FIG. 8Aillustrates a routine for controlling a command to be issued to the throttle valve17.FIG. 8Billustrates a routine for controlling a command to be issued to the intake air control valve19.FIG. 8Cillustrates a routine for controlling a command to be issued to the valve mechanism21.

In the routine illustrated inFIG. 8A, first of all in a step30, a current target opening TD(n) of the throttle valve17is calculated. Then, the target opening TD(n) is stored into the storage unit (not shown) in a step31. Then, a target opening TD(n-DP1) of the throttle valve17at a timing precedent to the present moment by a predetermined period DP1is read in a step32. Then, a command to equalize an opening of the throttle valve17with the target opening TD(n-DP1) read in the step32is issued in a step33. That is, according to this routine, the throttle valve17is so controlled as to assume the target opening after the lapse of a delay period that is equal to the sum of the predetermined period DP1and a response delay period of the throttle valve17.

In the routine illustrated inFIG. 8B, first of all in a step40, a current target operational state TS(n) of the intake air control valve19is calculated. Then, the target operational state TS(n) is stored into the storage unit (not shown) in a step41. Then, a target operational state TS(n-DP2) of the intake air control valve19at a timing precedent to the present moment by a predetermined period DP2is read in a step42. Then, a command to equalize an operational state of the intake air control valve19with the target operational state TS(n-DP2) read in the step42is issued in a step43. That is, according to this routine, the intake air control valve19is so controlled as to assume the target operational state after the lapse of a delay period that is equal to the sum of the predetermined period DP2and a response delay period of the intake air control valve19.

In the routine illustrated inFIG. 8C, first of all in a step50, a current target opening amount TA(n) of the intake valve7is calculated. Then, the target opening amount TA(n) is stored into the storage unit (not shown) in a step51. Then, a target opening amount TA(n-DP3) of the intake valve7at a timing precedent to the present moment by a predetermined period DP3is read in a step52. Then, a command to equalize an opening amount of the intake valve7with the target opening amount TA(n-DP3) read in the step52is issued in a step53. That is, according to this routine, the intake valve7is so controlled as to assume the target opening amount after the lapse of a delay period that is equal to the sum of the predetermined period DP3and a response delay period of the valve mechanism21.

Although only opening amount of the intake valve7is taken into account in the aforementioned embodiment, it is also appropriate that lift timing of the intake valve7be taken into account instead of or in addition to opening amount thereof.

According to the embodiments of the invention, a response delay period is set for each of the intake air amount control devices. Thus, it is possible to know how the respective intake air amount control devices will change in operational state before they actually do. Accordingly, it is possible to estimate in advance an amount of air drawn into the combustion chamber when the respective intake air amount control devices actually change in operational state in response to a depression stroke of the accelerator pedal. Namely, this makes it possible to precisely estimate an amount of air drawn into the combustion chamber.