Title of Invention

CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

Background of The Invention

Field of the Invention

[0001] '

The present invention relates to a control device that performs integrated control of an air amount, a fuel supply amount, and an ignition timing of an internal combustion engine that is configured to be capable of switching an air-fuel ratio that is used for operation between at least two target air-fuel ratios.

Background Art

[0002]

Japanese Patent Laid-Open No. 2007-231849 discloses technology (hereunder, referred to as "prior art") relating to air-fuel ratio switching control in an internal combustion engine that is capable of switching the operational air-fuel ratio of the internal combustion engine between a lean air-fuel ratio and a stoichiometric air-fuel ratio. According to the prior art, when switching the air-fuel ratio from a lean air-fuel ratio to the stoichiometric air-fuel ratio, the number of operating cylinders with which a minimum variation in the intake air amount is obtained when the torque is maintained is selected, and reduced-cylinder stoichiometric operation is executed that uses the cylinders corresponding to the relevant number of operating cylinders. If a torque level difference that corresponds to the variation in the intake air amount is greater than a predetermined value when executing the reduced-cylinder stoichiometric operation, the intake air amount is changed so as to maintain the torque, and a torque level difference that arises due to a delay in the actual response of the intake air amount is eliminated by performing ignition timing retardation control.

[Citation List]

[Patent Literature]

[0003] [Patent Literature 1]

Japanese Patent Laid-Open No. 2007-231849

[Patent Literature 2]

Japanese Patent Laid-Open No. 6-264786

[0004]

However, the possibility that fuel consumption will decrease accompanies retardation of the ignition timing. In particular, because a lean limit in lean-burn engines of recent years has increased, the difference in the required air amount between a stoichiometric air-fuel ratio and a lean air-fuel ratio has become extremely large. Therefore, when the above described prior art is applied to such lean-burn engines and it is attempted to suppress a torque level difference that is caused by a difference in air amounts by means of the ignition timing, there is a possibility that it will be necessary to continue a state in which the ignition timing is retarded by a large margin for an extended period, and there is thus a risk that a deterioration in the fuel consumption performance and the influence on the catalyst will be of an extent that cannot be overlooked.

[0005]

In this connection, when switching the air-fuel ratio, if the air-fuel ratio is gradually changed so as not to generate a torque level difference, the air-fuel ratio can be switched without performing ignition retardation control. However, if the air-fuel ratio is gradually changed from the stoichiometric air-fuel ratio to a lean air- fuel ratio, an increase in the amount of NOx emissions will become a problem. That is, there is a tendency for the amount of NOx emissions to reach a peak at a slightly lean air-fuel ratio of around 16, and thereafter decrease as the air-fuel ratio changes toward the lean side. Consequently, if the air-fuel ratio is gradually changed from the stoichiometric air-fuel ratio to a lean air-fuel ratio, the period of time that is required to pass through an air-fuel ratio region in which the amount of NOx emissions is large increases, and a deterioration in the exhaust performance becomes a problem.

Summary of the Invention

[0006]

The present invention has been conceived in view of the above described problems, and an object of the present invention is, in an internal combustion engine that is configured to be capable of switching an air-fuel ratio that is used for operation between at least two target air-fuel ratios, to switch the air-fuel ratio while suppressing fluctuations in the torque, and also suppress a deterioration in the fuel consumption performance and a deterioration in the exhaust performance at the time of switching.

[0007]

The present invention can be applied to the configuration of a control device for an internal combustion engine. Hereunder, a general outline of a control device for an internal combustion engine according to the present invention will be described. However, as will be apparent from the contents of the present invention described below, the present invention can be applied to the procedures of a control method for an internal combustion engine and can also be applied to an algorithm of a program that is executed with a control device.

[0008]

A control device for an internal combustion engine according to the present invention is a control device for an internal combustion engine that is configured to be capable of selecting operation according to a first air-fuel ratio and operation according to a second air-fuel ratio that is leaner than a third air-fuel ratio which is leaner than the first air-fuel ratio and also leaner than an air- fuel ratio at which an amount of NOx emissions with respect to the air-fuel ratio becomes a maximum, and that actuates air amount control means for controlling an air amount, air-fuel ratio control means for controlling the air-fuel ratio, and ignition timing control means for controlling an ignition timing, so as to achieve a requested torque,

wherein:

in a case where a condition for switching an operation mode from the operation according to the first air-fuel ratio to the operation according to the second air-fuel ratio is satisfied, the air amount control means controls a first actuator for changing an air amount so that the air amount becomes an air amount for achieving the requested torque under the second air-fuel ratio;

the air-fuel ratio control means configured to: in a case where the condition is satisfied,

(i) estimate an estimated air amount based on an operation amount of the first actuator,

(ii) maintain the air-fuel ratio at the first air-fuel ratio until the estimated air amount reaches an intermediate air amount for achieving the requested torque under the third air-fuel ratio, (iii) switche the air-fuel ratio in a step manner from the first air-fuel ratio to the third air-fuel ratio in response to the estimated air amount reaching the

intermediate air amount, and

(iv) after switching of the air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, control a second actuator for changing a fuel supply amount so as to change the air-fuel ratio in a continuous manner within a range from the third air- fuel ratio to the second air-fuel ratio based on the estimated air amount and the requested torque; and

the ignition timing control means controls a third actuator for changing the ignition timing so that a torque that is estimated based on the operation amount of the first actuator becomes the requested torque.

[0009]

More specifically, for example, the first actuator includes a throttle and a variable valve timing mechanism that varies a valve timing of an intake valve. In a case where a turbocharger is equipped with a supercharging property varying actuator that varies a supercharging property thereof, more specifically, a variable nozzle or a waste gate valve or the like, these can also be included in the first actuator. The second actuator is, specifically, an injector that injects fuel. For example, the second actuator includes a port injector that injects fuel into an intake port, and an in-cylinder injector that directly injects fuel into a cylinder. The third actuator is, specifically, an ignition device. The control device according to the present invention performs integrated control of an air amount, a fuel supply amount, and an ignition timing of the internal combustion engine by means of coordinated operations of these three kinds of actuators.

[0010]

The control device according to the present invention can be embodied by a computer. More specifically, the control device according to the present invention can be constituted by a computer that is equipped with a memory in which a program that describes processing for realizing various functions is stored, and a processor that reads the program from the memory and executes the program. Functions that the control device according to the present invention is equipped with include, as functions for determining a target air amount and a target air-fuel ratio to be used in coordinated operations of the three kinds of actuators described above, a requested torque reception function, a target air-fuel ratio switching function, a target air amount calculation function, and a parameter value changing function. [001 1]

According to the requested torque reception function, a requested torque with respect to the internal combustion engine is received. The requested torque is calculated based on a signal that is responsive to the degree of opening of an accelerator pedal that is operated by the driver. In a case where the driver issues a deceleration request with respect to the internal combustion engine, a requested torque is obtained that decreases in accordance with the speed at which the driver releases the accelerator pedal. In a case where the driver issues an acceleration request with respect to the internal combustion engine, a requested torque is obtained that increases in accordance with the speed at which the driver depresses the accelerator pedal.

[0012]

According to the target air amount calculation function, a target air amount for achieving the requested torque is back-calculated from the requested torque. A parameter that provides a conversion efficiency of the air amount to torque is used for calculating the target air amount. The parameter value is variable, and is changed by the parameter value changing function.

According to the parameter value changing function, in response to a condition for switching the operation mode from operation according to the first air-fuel ratio to operation according to the second air-fuel ratio being satisfied, the parameter value is changed in a direction that increases the air amount.

[0013]

Since the leaner the air-fuel ratio becomes relative to the theoretical air-fuel ratio, the greater the decrease in the amount of torque that is generated with the same air amount is, a parameter corresponding to the air-fuel ratio corresponds to a parameter that provides a conversion efficiency of the air amount to torque. The parameter value changing function can use a parameter corresponding to the air-fuel ratio as a parameter that provides a conversion efficiency of the air amount to torque. According to the parameter value changing function, in response to a condition for switching the operation mode from operation according to the first air- fuel ratio to operation according to the second air-fuel ratio being satisfied, the parameter value is changed from a value corresponding to the first air-fuel ratio to a value corresponding to the second air-fuel ratio. If the value of the requested torque is the same, the richer that the parameter corresponding to the air-fuel ratio is, the smaller that the target air amount becomes, while the leaner that the parameter is, the larger that the target air amount becomes.

[0014] According to the target air-fuel ratio switching function, after the parameter value is changed in a direction that increases the air amount, the target air-fuel ratio is switched from the first air-fuel ratio to a third air-fuel ratio that is between the first air-fuel ratio and the second air- fuel ratio, and thereafter is switched from the third air-fuel ratio to the second air-fuel ratio. That is, the target air-fuel ratio is not directly switched from the first air-fuel ratio to the second air-fuel ratio, but rather is temporarily switched to an intermediate third air-fuel ratio and is thereafter switched from the third air-fuel ratio to the second air-fuel ratio. Note that, the term "intermediate air-fuel ratio" used herein refers to an air-fuel ratio that is leaner than the first air- fuel ratio and is richer than the second air-fuel ratio, and is not limited to a median value between the first air-fuel ratio and the second air-fuel ratio. Specifically, the third air-fuel ratio is set to the value of an air-fuel ratio that is leaner than an air-fuel ratio at which the amount of NOx emissions discharged from inside the cylinders is a maximum amount.

[0015]

Specifically, the target air-fuel ratio switching function includes following first to fourth functions. The first function maintains the target air-fuel ratio at the first air-fuel ratio until an estimated air amount that is estimated based on an operation amount of the first actuator reaches an intermediate air amount with which the requested torque can be achieved under the third air- fuel ratio. The second function switches the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step manner in response to the estimated air amount reaching the intermediate air amount. After the target air-fuel ratio is switched from the first air-fuel ratio to the third air-fuel ratio, the third function changes the target air-fuel ratio in a continuous manner within a range from the third air-fuel ratio to the second air-fuel ratio based on the estimated air amount and the requested torque. In response to a difference between the target air amount and the estimated air amount becoming less than or equal to a threshold value, the fourth function fixes the target air-fuel ratio which has been changed based on the estimated air amount and the requested torque at the second air-fuel ratio.

[0016]

In particular, according to the third function a configuration is adopted that, for example, after switching of the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, changes the target air-fuel ratio in a continuous manner from the third air-fuel ratio to the second air-fuel ratio so that a torque that can be achieved by means of the estimated air amount at a predetermined ignition timing becomes the requested torque. [0017]

Further, according to the third function a configuration is adopted that, after switching of the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, calculates an amount of NOx emissions from inside cylinders at a predetermined ignition timing based on the target air-fuel ratio, and changes the target air-fuel ratio in a continuous manner within a range from the third air-fuel ratio to the second air-fuel ratio so that the amount of NOx emissions that is calculated. does not exceed a predetermined allowable limit.

[0018]

The control device according to the present invention subjects the three kinds of actuator to coordinated operations based on the target air amount and target air-fuel ratio determined by the above described processing. Functions that the control device of the present invention is equipped with include a first actuator control function, a second actuator control function and a third actuator control function as functions for performing coordinated operations based on the target air amount and target air-fuel ratio.

[0019]

According to the first actuator control function, an operation amount of the first actuator is determined based on the target air amount. Further, operation of the first actuator is performed in accordance with the determined operation amount. The actual air amount changes so as to track the target air amount according to the operation of the first actuator. In particular, in a case where the internal combustion engine is a supercharged engine including a supercharger, and the first actuator includes a supercharging property varying actuator that changes a supercharging property of the supercharger, in response to a condition for switching the operation mode from the operation according to the first air-fuel ratio to the operation according to the second air-fuel ratio being satisfied, whether or not a target intake pipe pressure that is calculated based on the target air amount reaches a supercharging region at a time point at which the target air-fuel ratio is switched to the second air-fuel ratio is estimated based on the requested torque. If it is estimated that the target intake pipe pressure reaches the supercharging region, the supercharging property varying actuator is actuated and a supercharging pressure of the supercharger is changed in an increasing direction.

[0020] According to the second actuator control function, a fuel supply amount is determined based on the target air-fuel ratio. Operation of the second actuator is then performed in accordance with the fuel supply amount that is determined.

[0021]

According to the third actuator control function, an ignition timing for achieving the requested torque is determined based on a torque that is estimated based on the operation amount of the first actuator and the target air-fuel ratio, and the requested torque. Operation of the third actuator is then performed in accordance with the determined ignition timing. The actual air amount can be estimated based on the operation amount of the first actuator, and the torque can be estimated based on the estimated air amount and the target air- fuel ratio. Operation of the third actuator is performed by correcting an excessive amount of the estimated torque with respect to the requested torque by means of the ignition timing.

[0022]

According to the control device of the present invention, in a case where a condition for switching from operation according to the first air-fuel ratio to operation according to the second air-fuel ratio is satisfied, although the air amount is increased, the air-fuel ratio is maintained at the first air-fuel ratio. As a result, the torque that can be achieved with the air amount and the air-fuel ratio is in excess of the requested torque, and retardation of the ignition timing is performed to compensate for the excessive amount of torque. Further, the air-fuel ratio is maintained at the first air-fuel ratio until an estimated air amount that is estimated based on the operation amount of an actuator reaches an intermediate air amount that can achieve the requested torque under the third air-fuel ratio, and in response to the estimated air amount reaching the intermediate air amount, the target air-fuel ratio is switched in a step manner from the first air- fuel ratio to the third air-fuel ratio. Since it is thereby possible to change the actual air-fuel ratio in a manner that skips a part of the air-fuel ratio region in which an amount of NOx emissions discharged from inside the cylinders is large, it is possible to suppress the amount of NOx emissions at the time that the air-fuel ratio is switched.

[0023]

After switching the air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, according to the control device of the present invention, changing of the target air-fuel ratio in a continuous manner is performed within a range from the third air-fuel ratio to the second air-fuel ratio based on the estimated air amount and the requested torque. Since the ignition retardation amount can be thereby decreased more than by changing the air-fuel ratio in a step manner from the third air-fuel ratio towards the second air-fuel ratio, it is possible to suppress the amount of NOx emissions and also suppress a deterioration in the fuel consumption performance by combining changing of the target air-fuel ratio from the third air-fuel ratio to the second air-fuel ratio in a continuous manner with the above described changing of the air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step manner.

[0024]

In particular, according to the functions of the control device of the present invention, while on one hand a parameter that provides a conversion efficiency of the air amount to torque that is used to calculate a target air amount is changed in a direction in which the air amount increases, the target air-fuel ratio is maintained at the first air-fuel ratio. As a result, the torque that can be achieved with the target air amount and the target air-fuel ratio is in excess of the requested torque, and retardation of the ignition timing is performed to compensate for the excessive amount of torque. Further, the target air-fuel ratio is maintained at the first air-fuel ratio until an estimated air amount that is estimated based on the operation amount of the first actuator reaches an intermediate air amount that can achieve the requested torque under the third air-fuel ratio, and in response to the estimated air amount reaching the intermediate air amount, the target air-fuel ratio is switched in a step manner from the first air-fuel ratio to the third air-fuel ratio. Since it is thereby possible to change the actual air-fuel ratio in a manner that skips a part of the air-fuel ratio region in which the amount of NOx emissions discharged from inside the cylinders is large, it is possible to suppress the amount of NOx emissions at the time that the air- fuel ratio is switched.

[0025]

After switching the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, the control device according to the present invention changes the target air-fuel ratio in a continuous manner within a range from the third air-fuel ratio to the second air-fuel ratio based on the estimated air amount and the requested torque. Since the ignition retardation amount can be thereby decreased more than by changing the target air-fuel ratio in a step manner from the third air-fuel ratio towards the second air-fuel ratio, it is possible to suppress the amount of NOx emissions and also suppress a deterioration in the fuel consumption performance by combining changing of the target air-fuel ratio from the third air-fuel ratio to the second air-fuel ratio in a continuous manner with the above described changing of the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step manner.

[0026]

In particular, according to the third function, for example, after switching of the target air- fuel ratio from the first air-fuel ratio to the third air-fuel ratio, changing of the target air-fuel ratio in a continuous manner is performed within a range from the third air-fuel ratio to the second air- fuel ratio so that the torque that can be achieved by means of the estimated air amount at a predetermined ignition timing becomes the requested torque. It is thereby possible to further suppress the amount of retardation of the ignition timing.

[0027]

In addition, according to the third function, after switching of the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, it is also possible to calculate the amount of NOx emissions from inside the cylinders with respect to a predetermined ignition timing based on the target air-fuel ratio, and the target air-fuel ratio can be changed in a continuous manner within a range from the third air-fuel ratio to the second air-fuel ratio so that the calculated amount of NOx emissions does not exceed a predetermined allowable limit. It is thereby possible to switch the air-fuel ratio while ensuring that the amount of NOx emissions does not exceed a

predetermined allowable limit.

[0028]

Note that, in a case where the internal combustion engine is a supercharged engine equipped with a supercharger, and the first actuator includes a supercharging property varying actuator that changes a supercharging property of the supercharger, since the supercharging property varying actuator is operated so that supercharging of the supercharger changes in an increasing direction during switching of the air-fuel ratio, the responsiveness of the air can be increased and the time required to switch the air-fuel ratio can be shortened. Further, in a case where the supercharging property varying actuator is a waste gate valve, since the back pressure increases when the waste gate valve is closed, it is possible to further reduce the amount of NOx emissions by increasing the internal EGR rate during switching of the air-fuel ratio.

Brief Description of Drawings

[0029] Fig. 1 is a block diagram illustrating the logic of a control device according to a first embodiment of the present invention.

Fig. 2 is a block diagram illustrating the logic of switching operation modes in the control device according to the first embodiment of the present invention.

Fig. 3 shows an image of a map showing a relation between the air amount and the torque with respect to a predetermined torque efficiency.

Fig. 4 is a view illustrating the relation with the amount of NOx emissions with respect to an air-fuel ratio.

Fig. 5 is a flowchart illustrating the logic of switching target air-fuel ratio for the control device according to the first embodiment of the present invention.

Fig. 6 is a time chart that illustrates an image of results of control performed by the control device according to the present embodiment.

Fig. 7 is a view illustrating the relation of the amount of NOx emissions with respect to the air-fuel ratio.

Fig. 8 illustrates settings of operating ranges according to the present embodiment of the present invention.

Detailed Description of Preferred Embodiments

[0030]

[First Embodiment]

Hereunder, a first embodiment of the present invention is described with reference to the drawings.

[0031]

An internal combustion engine (hereinafter, referred to as "engine") which is a control object in the present embodiment is a spark-ignition type, four-cycle reciprocating engine, and is a turbo-engine in which a turbocharger is installed. Further, the engine is a so-called "lean-burn engine" that is constructed so as to be capable of selecting between a stoichiometric mode (first operation mode) that performs operation according to a theoretical air-fuel ratio and a lean mode (second operation mode) that performs operation according to an air-fuel ratio that is leaner than the theoretical air-fuel ratio as operation modes of the engine.

[0032] An ECU (Electrical Control Unit) mounted in the vehicle controls operations of the engine by actuating various kinds of actuators that are provided in the engine. The actuators actuated by the ECU include a throttle and variable valve timing mechanism (hereunder, referred to as "VVT") as a first actuator that changes an air amount, an injector as a second actuator that supplies fuel into a cylinder, and an ignition device as a third actuator that ignites an air-fuel mixture in a cylinder. The VVT is provided with respect to an intake valve. The injector is provided in an intake port. The ECU actuates these actuators to control operation of the engine. Control of the engine by the ECU includes switching of the operation mode from a stoichiometric mode to a lean mode, or from the lean mode to the stoichiometric mode.

[0033]

In Fig. 1, the logic of the ECU according to the present embodiment is illustrated in a block diagram. The ECU includes an engine controller 100 and a powertrain manager 200. The engine controller 100 is a control device that directly controls the engine, and corresponds to the control device according to the present invention. The powertrain manager 200 is a control device that performs integrated control of the entire driving system that includes the engine, an electronically controlled automatic transmission, and also vehicle control devices such as a VSC and TRC. The engine controller 100 is configured to control operation of the engine based on signals received from the powertrain manager 200. The engine controller 100 and powertrain manager 200 are each realized by software. More specifically, the respective functions of the engine controller 100 and the powertrain manager 200 are realized in the ECU by reading programs stored in a memory and executing the programs using a processor.

[0034]

In the block showing the powertrain manager 200 in Fig. 1, among various functions that the powertrain manager 200 is equipped with, some of the functions relating to control of the engine are represented by blocks. An arithmetic unit is allocated to each of these blocks. A program corresponding to each block is prepared in the ECU, and the functions of the respective arithmetic units are realized in the ECU by executing the programs using a processor.

[0035]

An arithmetic unit 202 calculates a requested first torque and sends the calculated value to the engine controller 100. In Fig. 1, the requested first torque is described as "TQlr". The first torque is a torque of a kind with respect to which the responsiveness required of the engine is not high and which it is sufficient to realize in the near future and need not be realized immediately. The requested first torque is a requested value of the first torque that the powertrain manager 200 requests with respect to the engine, and corresponds to the requested torque in the present invention. A signal that is output in response to the state of the degree of opening of the accelerator pedal from an unshown accelerator position sensor is input to the arithmetic unit 202. The requested first torque is calculated based on the aforementioned signal. Note that the requested first torque is a shaft torque.

[0036]

An arithmetic unit 204 calculates a requested second torque and sends the calculated value to the engine controller 100. In Fig. 1, the requested second torque is described as "TQ2r". The second torque is a torque of a kind with respect to which the urgency or priority is higher than the first torque and for which a high responsiveness is required of the engine. That is, the second torque is of a kind which is required to be realized immediately. The term

"responsiveness" used here refers to the responsiveness when the torque is temporarily decreased. The requested second torque is a requested value of the second torque that the powertrain manager 200 requests with respect to the engine. The requested second torque that is calculated by the arithmetic unit 204 includes various kinds of torques requested from the vehicle control system, such as a torque requested for transmission control of the electronically controlled automatic transmission, a torque requested for traction control, and a torque requested for sideslip prevention control. While the first torque is a torque that the engine is required to generate stably or over an extended period, the second torque is a torque that the engine is required to generate suddenly or during a short period. Therefore, the arithmetic unit 204 outputs a valid value that is in accordance with the size of the torque that it is desired to realize only in a case where an event has actually arisen in which such a torque is required, and outputs an invalid value during a period in which such an event does not arise. The invalid value is set to a value that is larger than the maximum shaft torque that the engine can output.

[0037]

An arithmetic unit 206 calculates a transmission gear ratio of the automatic transmission, and sends a signal indicating the transmission gear ratio to an unshown transmission controller. The transmission controller is realized as one function of the ECU, similarly to the powertrain manager 200 and the engine controller 100. A flag signal from the engine controller 100 is input to the arithmetic unit 206. In the drawings, the flag signal is described as "FLG". The flag signal is a signal that indicates that the state is one in which switching of the operation mode is being performed. During a period in which the flag signal is "on", the arithmetic unit 206 fixes the transmission gear ratio of the automatic transmission.

[0038]

In response to a predetermined condition being satisfied, an arithmetic unit 208 sends a stop signal to the engine controller 100 that instructs the engine controller 100 to stop switching of the operation mode. In the drawings, the stop signal is described as "Stop". The

predetermined condition is that a request to change the operating state of the engine to a large degree is output from the powertrain manager 200.

[0039]

Next, the configuration of the engine controller 100 will be described. Interfaces 101 , 102, 103 and 104 are arranged between the engine controller 100 and the powertrain manager 200. The interface 101 corresponds to requested torque reception means in the present invention.

The requested first torque is passed to the engine controller 100 at the interface 101. The stop signal is passed to the engine controller 100 at the interface 102. The flag signal is passed to the engine controller 100 at the interface 103. The requested second torque is passed to the engine controller 100 at the interface 104.

[0040]

In the block illustrating the engine controller 100 in Fig. 1 , among the various functions with which the engine controller 100 is equipped, functions relating to coordinated operations of the three kinds of actuators, that is, a throttle 2 and a VVT 8 as a first actuator, an injector 4 as a second actuator, and an ignition device 6 as a third actuator are represented with blocks. An arithmetic unit is allocated to each of these blocks. A program corresponding to each block is prepared in the ECU, and the functions of the respective arithmetic units are realized in the ECU by executing the programs using a processor.

[0041]

The configuration of the engine controller 100 is broadly divided into three large arithmetic units 120, 140 and 160. The large arithmetic unit 120 calculates values of various control parameters with respect to the engine. The control parameters include target values of various control amounts with respect to the engine. In addition, the target values include a value calculated based on a requested value sent from the powertrain manager 200, and a value that is calculated within the large arithmetic unit 120 based on information relating to the operating state of the engine. Note that, while a requested value is a value of a control amount that is unilaterally requested from the powertrain manager 200 without taking the state of the engine into consideration, a target value is a value of a control amount that is set based on a realizable range that is decided depending on the state of the engine. The large arithmetic unit 120 is, more specifically, constituted by four arithmetic units 122, 124, 126, and 128.

[0042]

The arithmetic unit 122 calculates, as control parameters for the engine, a target air-fuel ratio, a virtual air-fuel ratio, a target efficiency for switching, and a target second torque for switching. In the drawings, the target air-fuel ratio is described as "AFt", the virtual air-fuel ratio is described as "AFh", the target efficiency for switching is described as " tc", and the target second torque for switching is described as "TQ2c". The target air-fuel ratio is a target value of the air-fuel ratio to be realized by the engine, and is used for calculating a fuel injection amount. On the other hand, the virtual air-fuel ratio is a parameter that provides a conversion efficiency of the air amount to torque, and is used for calculating a target air amount. The target efficiency for switching is a target value of the ignition timing efficiency for switching of the operation mode, and is used for calculating the target air amount. The term "ignition timing efficiency" refers to the proportion of torque that is actually output with respect to the torque that can be output when the ignition timing is the optimal ignition timing. When the ignition timing is the optimal ignition timing, the ignition timing efficiency is 1 that is the maximum value thereof. Note that the term "optimal ignition timing" fundamentally refers to the MBT (minimum advance for best torque), and when a trace knock ignition timing is set, the term "optimal ignition timing" refers to the ignition timing that is located further on the retardation side among the MBT and the trace knock ignition timing. The target second torque for switching is a target value of the second torque for switching of the operation mode, and is used to switch the calculation of the ignition timing efficiency when switching the operation mode. Switching of the operation mode is executed by combining the values of these control parameters that are calculated with the arithmetic unit 122. The relation between the contents of the processing performed by the arithmetic unit 122 and switching of the operation mode will be described in detail later.

[0043]

In addition to the requested first torque, the requested second torque, and the stop signal that are received from the powertrain manager 200, various kinds of information relating to the operating state of the engine such as engine speed is also input to the arithmetic unit 122.

Among these various kinds of information, the requested first torque is used as information for determining the timing for switching the operation mode. The requested second torque and the stop signal are used as information for determining whether switching of the operation mode is permitted or prohibited. When the stop signal is inputted, and when the requested second torque of a valid value is inputted, the arithmetic unit 122 does not execute processing relating to switching the operation mode. Further, during switching of the operation mode, that is, while executing calculation processing for switching the operation mode, the arithmetic unit 122 sends the aforementioned flag signal to the powertrain manager 200.

[0044]

The arithmetic unit 124 calculates, as a control parameter for the engine, a torque that is classified as a first torque among torques that are necessary for maintaining the current operating state of the engine or for realizing a scheduled predetermined operating state. In this case, the torque that is calculated by the arithmetic unit 124 is referred to as "other first torque". In the drawings, the other first torque is described as "TQletc". The arithmetic unit 124 outputs a valid value only in a case where such a torque is actually required, and calculates an invalid value during a period in which such a torque is not required.

[0045]

The arithmetic unit 126 calculates, as a control parameter for the engine, a torque that is classified as a second torque among torques that are necessary for maintaining the current operating state of the engine or for realizing a scheduled predetermined operating state. In this case, the torque that is calculated by the arithmetic unit 126 is referred to as "other second torque". In the drawings, the other second torque is described as "TQ2etc". The arithmetic unit 126 outputs a valid value only in a case where such a torque is actually required, and calculates an invalid value during a period in which such a torque is not required.

[0046]

The arithmetic unit 128 calculates, as a control parameter for the engine, an ignition timing efficiency that is necessary for maintaining the current operating state of the engine or for realizing a scheduled predetermined operating state. In this case, the ignition timing efficiency that is calculated by the arithmetic unit 128 is referred to as "other efficiency" . In the drawings, the other efficiency is described as "netc". An ignition timing efficiency that is necessary for warming up an exhaust purification catalyst when starting the engine is included in the other efficiency. The more the ignition timing efficiency is lowered, the less the amount of energy that is converted to torque will be among the energy generated by the combustion of fuel, and thus an amount of energy that is increased by an amount corresponding to the decrease in the energy converted to torque will be discharged to the exhaust passage together with the exhaust gas and used to warm up the exhaust purification catalyst. Note that, during a period in which it is not necessary to realize such efficiency, the efficiency value outputted from the arithmetic unit 128 is held at a value of 1 that is the maximum value.

[0047]

The requested first torque, the other first torque, the target air-fuel ratio, the virtual air- fuel ratio, the target efficiency for switching, the other efficiency, the requested second torque, the target second torque for switching, and the other second torque are outputted from the large arithmetic unit 120 configured as described above. These control parameters are input to the large arithmetic unit 140. Note that, although the requested first torque and the requested second torque that are received from the powertrain manager 200 are shaft torques, conversion of these torques into indicated torques is performed at the large arithmetic unit 120. Conversion of the requested torque to the indicated torque is performed by adding or subtracting a friction torque, an auxiliary driving torque and a pump loss to or from the requested torque. Note that, torques such as the target second torque for switching that are calculated within the large arithmetic unit 120 are each calculated as an indicated torque.

[0048]

Next, the large arithmetic unit 140 will be described. As described above, various engine control parameters are sent to the large arithmetic unit 140 from the large arithmetic unit 120. Among these, the requested first torque and the other first torque are requests with respect to control amounts that belong to the same category, and these cannot be realized simultaneously. Likewise, the requested second torque, the other second torque and the target second torque for switching are requests with respect to control amounts that belong to the same category, and these cannot be realized simultaneously. Likewise, the target efficiency for switching and the other efficiency are requests with respect to control amounts that belong to the same category, and these cannot be realized simultaneously. Consequently, processing is necessary that performs a mediation process for each control amount category. As used herein, the term "mediation" refers to a computation process for obtaining a single numerical value from a plurality of numerical values, such as, for example, selecting a maximum value, selecting a minimum value, averaging, or superimposing, and a configuration can also be adopted in which the mediation process appropriately combines a plurality of kinds of computation processes. To execute such kind of mediation for each control amount category, the large arithmetic unit 140 includes three arithmetic units 142, 144, and 146.

[0049]

The arithmetic unit 142 is configured to perform a mediation process with respect to the first torque. The requested first torque and the other first torque are inputted to the arithmetic unit 142. The arithmetic unit 142 performs a mediation process on these values, and outputs a torque that is obtained as the mediation result as a target first torque that is finally determined. In Fig. 1, the finally determined target first torque is described as "TQlt". Minimum value selection is used as the mediation method in the arithmetic unit 142. Accordingly, in a case where a valid value is not output from the arithmetic unit 124, the requested first torque that is provided from the powertrain manager 200 is calculated as the target first torque.

[0050]

The arithmetic unit 144 is configured to perform a mediation process with respect to the ignition timing efficiency. The target efficiency for switching and the other efficiency are inputted to the arithmetic unit 144. The arithmetic unit 144 performs a mediation process on these values, and outputs an efficiency that is obtained as the mediation result as a target efficiency that is finally determined. In Fig. 1 , the finally determined target efficiency is described as "nt". Minimum value selection is used as the mediation method in the arithmetic unit 144. From the viewpoint of fuel consumption performance, it is preferable that the ignition timing efficiency is 1 which is the maximum value thereof. Therefore, as long as no special event occurs, the target efficiency for switching that is calculated by the arithmetic unit 122 and the other efficiency that is calculated by the arithmetic unit 128 are each maintained at a value of 1 that is the maximum value. Accordingly, the value of the target efficiency that is output from the arithmetic unit 144 is fundamentally 1, and a value that is less than 1 is only selected in a case where an event of some kind has occurred.

[0051]

The arithmetic unit 146 is configured to perform a mediation process with respect to the second torque. The requested second torque, the other second torque, and the target second torque for switching are inputted to the arithmetic unit 146. The arithmetic unit 146 performs a mediation process on these values, and outputs a torque that is obtained as the mediation result as a target second torque that is finally determined. In Fig. 1 , the finally determined target second torque is described as "TQ2t". Minimum value selection is used as the mediation method in the arithmetic unit 146. The second torque, including the target second torque for switching, is fundamentally an invalid value, and is switched to a valid value showing the size of the torque it is desired to realize only in a case where a specific event has occurred. Accordingly, the target second torque that is output from the arithmetic unit 146 is also fundamentally an invalid value, and a valid value is selected in only a case where an event of some kind has occurred.

[0052]

The target first torque, the target efficiency, the virtual air-fuel ratio, the target air-fuel ratio, and the target second torque are output from the large arithmetic unit 140 that is configured as described above. These control parameters are input to the large arithmetic unit 160.

[0053]

The large arithmetic unit 160 corresponds to an inverse model of the engine, and is constituted by a plurality of models that are represented by a map or a function. Operation amounts of the respective actuators 2, 4, 6, and 8 for coordinated operations are calculated by the large arithmetic unit 160. Among the control parameters that are inputted from the large arithmetic unit 140, the target first torque and the target second torque are each handled as target values of the torque with respect to the engine. However, the target second torque takes priority over the target first torque. In the large arithmetic unit 160, calculation of operation amounts of the respective actuators 2, 4, 6, and 8 is performed so as to achieve the target second torque in a case where the target second torque is a valid value, or so as to achieve the target first torque in a case where the target second torque is an invalid value. Calculation of the operation amounts is performed so as to also achieve the target air-fuel ratio and the target efficiency simultaneously with the target torque. That is, according to the control device of the present embodiment, the torque, the efficiency and the air-fuel ratio are used as control amounts of the engine, and air amount control, ignition timing control and fuel injection amount control is conducted based on the target values of these three kinds of control amounts.

[0054]

The large arithmetic unit 160 includes a plurality of arithmetic units 162, 164, 166, 168, 170, 172, 174, 176, and 178. Among these arithmetic units, the arithmetic units 162, 164, 166, and 178 relate to air amount control, the arithmetic units 168, 170, and 172 relate to ignition timing control, and the arithmetic units 174 and 176 relate to fuel injection amount control. Hereunder, the functions of the respective arithmetic units are described in detail in order, starting from the arithmetic units relating to air amount control. [0055]

The target first torque, the target efficiency and the virtual air-fuel ratio are inputted to the arithmetic unit 162. The arithmetic unit 162 corresponds to target air amount calculation means of the present invention, and uses the target efficiency and the virtual air-fuel ratio to back- calculate a target air amount for achieving the target first torque from the target first torque. In this calculation, the target efficiency and the virtual air-fuel ratio are used as parameters that provide a conversion efficiency of the air amount to torque. Note that, in the present invention, the term "air amount" refers to the amount of air that is drawn into the cylinders, and a charging efficiency or a load factor, which are non-dimensional equivalents of the air amount, are within an equivalent range to the air amount in the present invention.

[0056]

The arithmetic unit 162 first calculates a target torque for air amount control by dividing the target first torque by the target efficiency. If the target efficiency is less than 1 , the target torque for air amount control becomes larger than the target first torque. This means that a requirement with respect to the air amount control by the actuators 2 and 8 is to enable the potential output of torque that is greater than the target first torque. On the other hand, if the target efficiency is 1, the target first torque is calculated as it is as the target torque for air amount control.

[0057]

Next, the arithmetic unit 162 converts the target torque for air amount control to a target air amount using a torque-air amount conversion map. The torque-air amount conversion map is prepared on the premise that the ignition timing is the optimal ignition timing, and is a map in which the torque and the air amount are associated using various engine status amounts, such as the engine speed and the air-fuel ratio as keys. This map is created based on data obtained by testing the engine. Actual values or target values of the engine status amounts are used to search the torque-air amount conversion map. With regard to the air-fuel ratio, the virtual air-fuel ratio is used to search the map. Accordingly, at the arithmetic unit 162, the air amount that is required to realize the target torque for air amount control under the virtual air-fuel ratio is calculated as the target air amount. In the drawings, the target air amount is described as "KLt".

[0058]

The arithmetic unit 164 back-calculates a target intake pipe pressure that is a target value of the intake pipe pressure from the target air amount. A map that describes the relation between an air amount that is drawn into the cylinders through the intake valve and the intake pipe pressure is used to calculate the target intake pipe pressure. The relation between the air amount and the intake pipe pressure changes depending on the valve timing. Therefore, when calculating the target intake pipe pressure, a parameter value of the aforementioned map is determined based on the current valve timing. The target intake pipe pressure is described as "Pmt" in the drawings.

[0059]

The arithmetic unit 166 calculates a target degree of throttle opening that is a target value of the degree of throttle opening based on the target intake pipe pressure. An inverse model of the air model is used to calculate the target degree of throttle opening. The air model is a physical model which is obtained as the result of modeling the response characteristic of the intake pipe pressure with respect to operation of the throttle 2. Therefore, the target degree of throttle opening that is required to achieve the target intake pipe pressure can be back-calculated from the target intake pipe pressure using the inverse model thereof. The target degree of throttle opening is described as "TA" in the drawings. The target degree of throttle opening calculated by the arithmetic unit 166 is converted to a signal for driving the throttle 2, and is sent to the throttle 2 through an interface 11 1 of the ECU. The arithmetic units 164 and 166 correspond to first actuator control means according to the present invention.

[0060]

The arithmetic unit 178 calculates a target valve timing that is a target value of the valve timing based on the target air amount. A map in which the air amount and the valve timing are associated using the engine speed as an argument is utilized to calculate the target valve timing. The target valve timing is the optimal displacement angle of the VVT 8 for achieving the target air amount based on the current engine speed, and the specific value thereof is determined by adaptation for each air amount and each engine speed. The target valve timing is described as "VT" in the drawings. The target valve timing calculated by the arithmetic unit 178 is converted to a signal for driving the VVT 8, and is sent to the VVT 8 through an interface 1 12 of the ECU. The arithmetic unit 178 also corresponds to first actuator control means in the present invention.

[0061]

Next, the functions of the arithmetic units relating to ignition timing control will be described. The arithmetic unit 168 calculates an estimated torque based on the actual degree of throttle opening and the valve timing realized by the above described air amount control. The term "estimated torque" as used in the present description refers to torque that can be output in a case where the ignition timing is set to the optimal ignition timing based on the current degree of throttle opening and valve timing and the target air-fuel ratio. The arithmetic unit 168 first calculates . an estimated air amount based on a measured value of the degree of throttle opening and a measured value of the valve timing using a forward model of the aforementioned air model. The estimated air amount is an estimated value of an air amount that is actually realized by the current degree of throttle opening and valve timing. Next, the arithmetic unit 168 converts the estimated air amount to an estimated torque using the torque-air amount conversion map. The target air-fuel ratio is used as a search key when searching the torque-air amount conversion map. The estimated torque is described as "TQe" in the drawings.

[0062]

The target second torque and the estimated torque are inputted to the arithmetic unit 170. The arithmetic unit 170 calculates an indicated ignition timing efficiency that is an indicated value of the ignition timing efficiency based on the target second torque and the estimated torque. The indicated ignition timing efficiency is expressed as a proportion of the target second torque to the estimated torque. However, an upper limit is defined for the indicated ignition timing efficiency, and the value of the indicated ignition timing efficiency is set as 1 in a case where the proportion of the target second torque with respect to the estimated torque exceeds 1. The indicated ignition timing efficiency is described as "ηϊ" in the drawings.

[0063]

The arithmetic unit 172 calculates the ignition timing based on the indicated ignition timing efficiency. More specifically, the arithmetic unit 172 calculates the optimal ignition timing based on engine status amounts such as the engine speed, the requested torque and the air- fuel ratio, and calculates a retardation amount with respect to the optimal ignition timing based on the indicated ignition timing efficiency. When the indicated ignition timing efficiency is 1, the retardation amount is set as zero, and the retardation amount is progressively increased as the indicated ignition timing efficiency decreases from 1. The arithmetic unit 172 then calculates the result of addition of the retardation amount to the optimal ignition timing as a final ignition timing. However, the final ignition timing is restricted by a retardation limit guard. The term "retardation limit" refers to the most retarded ignition timing at which it is guaranteed that misfiring will not occur, and the retardation limit guard guards the final ignition timing so that the ignition timing is not retarded beyond the retardation limit. A map in which the optimal ignition timing and various engine status amounts are associated can be used to calculate the optimal ignition timing. A map in which the retardation amount, the ignition timing efficiency and various engine status amounts are associated can be used to calculate the retardation amount. The target air-fuel ratio is used as a search key to search these maps. The ignition timing is described as "SA" in the drawings. The ignition timing calculated by the arithmetic unit 172 is converted to a signal for driving the ignition device 6, and is sent to the ignition device 6 through an interface 1 13 of the ECU. The arithmetic units 168, 170 and 172 correspond to third actuator control means in the present invention.

[0064]

Next, functions of the arithmetic units relating to fuel injection amount control will be described. The arithmetic unit 174 calculates an estimated air amount based on a measured value of the degree of throttle opening and a measured value of the valve timing using the forward model of the air model described above. The estimated air amount calculated by the arithmetic unit 174 is preferably an air amount that is predicted to arise at a timing at which the intake valve closes. An air amount that will arise in the future can be predicted, for example, based on the target degree of throttle opening by setting a delay time period from calculation of the target degree of throttle opening until the output thereof. The estimated air amount is described as "KLe" in the drawings.

[0065]

The arithmetic unit 176 calculates a fuel injection amount, that is, a fuel supply amount, that is required to achieve the target air-fuel ratio based on the target air-fuel ratio and the estimated air amount. Calculation of the fuel injection amount is executed when the timing for calculating a fuel injection amount arrives with respect to each cylinder. The fuel injection amount is described as "TAU" in the drawings. The fuel injection amount calculated by the arithmetic unit 176 is converted to a signal for driving the injector 4, and is sent to the injector 4 through an interface 1 14 of the ECU. The arithmetic units 174 and 176 correspond to second actuator control means in the present invention.

[0066]

The foregoing is an overview of the logic of the ECU according to the present embodiment. Next, the arithmetic unit 122 that is a main portion of the ECU according to the present embodiment will be described in detail.

[0067] The logic of the arithmetic unit 122 is illustrated by means of a block diagram in Fig. 2. Inside the block illustrating the arithmetic unit 122 in Fig. 2, among the various functions that the arithmetic unit 122 is equipped with, functions relating to switching of the operation mode are represented by blocks. An arithmetic unit is allocated to each of these blocks. A program corresponding to each block is prepared in the ECU, and the functions of the respective arithmetic units are realized in the ECU by executing the programs using a processor.

[0068]

First, an arithmetic unit 402 will be described. The arithmetic unit 402 calculates a reference value for the torque. The reference value is a torque that serves as a boundary between a lean mode and a stoichiometric mode, and the optimal value is adapted for each engine speed from the viewpoint of fuel consumption performance, exhaust gas performance and drivability. The arithmetic unit 402 refers to a previously prepared map to calculate a reference value that is suitable for the engine speed. The reference value is described as "Ref in the drawings.

[0069]

Next, the arithmetic unit 404 will be described. The requested first torque is inputted to the arithmetic unit 404. In addition, the reference value calculated by the arithmetic unit 402 is set with respect to the arithmetic unit 404. The arithmetic unit 404 changes a value of the virtual air-fuel ratio that is used to calculate the target air amount, based on the relation between the requested first torque and the reference value that are inputted. More specifically, the arithmetic unit 404 switches the virtual air-fuel ratio from a first air-fuel ratio to a second air-fuel ratio or from the second air-fuel ratio to the first air-fuel ratio. The first air-fuel ratio is the theoretical air-fuel ratio (for example, 14.6). The first air-fuel ratio is described as "AF1 " in the drawings. The second air-fuel ratio is a leaner air-fuel ratio than the first air-fuel ratio, and is set to a certain fixed value (for example, 26.0). The second air-fuel ratio is described as "AF2" in the drawings. The arithmetic unit 404 corresponds to parameter value changing means in the present invention. During a period in which the requested first torque is greater than the reference value, the arithmetic unit 404 sets the virtual air-fuel ratio to the first air-fuel ratio in response to the requested first torque being greater than the reference value. If the requested first torque decreases in accordance with a deceleration request of the driver and in due course becomes less than the reference value, the arithmetic unit 404 switches the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio in response to the requested first torque decreasing to a value that is less than or equal to the reference value.

[0070]

Next, the arithmetic unit 406 will be described. The requested first torque is inputted to the arithmetic unit 406. The arithmetic unit 406 converts the requested first torque to an air amount using the torque-air amount conversion map. A third air-fuel ratio that is an air-fuel ratio that lies between the first air-fuel ratio and the second air-fuel ratio, that is, an air-fuel ratio that is leaner than the first air-fuel ratio and is richer than the second air-fuel ratio is used to search the torque-air amount conversion map. The third air-fuel ratio is described as "AF3" in the drawings. Accordingly, an air amount that is necessary to realize the requested first torque under the third air-fuel ratio is calculated by the arithmetic unit 406. Hereunder, the air amount that is calculated by the arithmetic unit 406 is referred to as "intermediate air amount" and is described as "KLi" in the drawings.

[0071]

Next, the arithmetic unit 408 will be described. Together with the arithmetic unit 406, the arithmetic unit 408 constitutes target air-fuel ratio switching means of the present invention. The first air-fuel ratio that is used in the stoichiometric mode and the second air-fuel ratio that is used in the lean mode are previously set as default values of the target air-fuel ratio in the arithmetic unit 408. In addition, the third air- fuel ratio that is an intermediate air-fuel ratio is previously set therein. Note that, a specific value of the third air-fuel ratio is determined by adaptation based on the relation with the retardation limit of the ignition timing and the relation with the exhaust performance, and a description regarding determination of the specific value is provided later. The virtual air-fuel ratio determined by the arithmetic unit 404, the intermediate air amount calculated by the arithmetic unit 406, a value of the target air amount calculated in a previous step by the arithmetic unit 162, and a value of the estimated air amount calculated in a previous step by the arithmetic unit 174 are inputted to the arithmetic unit 408. Further, an AF conversion map for determining the air-fuel ratio necessary to achieve the requested first torque under a condition of the ignition timing corresponding to the predetermined torque efficiency and the current estimated air amount is created in the arithmetic unit 408. The term "torque efficiency" used here refers to the efficiency with respect to converting the air amount to torque. Fig. 3 shows an image of a map showing a relation between the air amount and the torque with respect to a predetermined torque efficiency. As shown in Fig. 3, if the torque efficiency is constant, the size of the torque that can be achieved with the same air amount depends on the air- fuel ratio. Hence, the target air-fuel ratio for achieving the requested first torque based on a predetermined torque efficiency changes in a continuous manner to the lean side as the current estimated air amount increases.

[0072]

Upon detecting that the virtual air-fuel ratio that is inputted from the arithmetic unit 404 was switched from the first air-fuel ratio to the second air-fuel ratio, the arithmetic unit 408 performs a comparison between the intermediate air amount and the estimated air amount for each series of control operations executed by the arithmetic unit 408. Immediately after the virtual air-fuel ratio is switched from the first air-fuel ratio to the second air-fuel ratio, the estimated air amount becomes a smaller value than the intermediate air amount. Further, since the estimated torque is a larger value than the requested first torque, the indicated ignition timing efficiency becomes a value that is less than 1 , and retardation of the ignition timing is performed. When the estimated air amount arrives at the intermediate air amount in due course, the arithmetic unit 408 rapidly switches the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step manner at that time point. Immediately after the target air-fuel ratio is switched from the first air-fuel ratio to the third air-fuel ratio, the estimated air amount matches the intermediate air amount. Further, since the estimated torque becomes the requested first torque, the indicated ignition timing efficiency becomes 1 and the ignition timing becomes the optimal ignition timing.

[0073]

After switching of the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio, the arithmetic unit 408 switches the target air-fuel ratio to an air-fuel ratio that is determined by means of the AF conversion map. Calculation of the target air-fuel ratio using the AF conversion map is performed for each series of control operations that is executed by the arithmetic unit 408 using the map illustrated in Fig. 3. Subsequently, when the estimated air amount becomes sufficiently near to the target air amount, specifically, when a difference between the target air amount and the estimated air amount becomes less than or equal to a predetermined threshold value, the arithmetic unit 408 fixes the target air-fuel ratio at the second air-fuel ratio. That is, after the virtual air-fuel ratio is switched from the first air-fuel ratio to the second air-fuel ratio, the target air-fuel ratio is temporarily switched in a step manner from the first air-fuel ratio to the third air-fuel ratio that is the intermediate air-fuel ratio, and thereafter is switched in a continuous manner from the third air-fuel ratio to the second air-fuel ratio. That is, after the target air-fuel ratio is instantly switched from the first air-fuel ratio to the third air-fuel ratio, switching from the third air-fuel ratio to the second air-fuel ratio is performed by switching to air-fuel ratios between the third air-fuel ratio and the second air-fuel ratio so as to gradually approach the second air-fuel ratio and finally arrive at the second air-fuel ratio. The operation mode is switched from the stoichiometric mode to the lean mode by switching the target air-fuel ratio.

[0074]

Note that, the specific value of the third air-fuel ratio is determined by adaptation based on the relation with the retardation limit of the ignition timing and the relation with the exhaust performance. Fig. 4 is a view illustrating the relation with the amount of NOx emissions from the cylinders with respect to an air-fuel ratio at a predetermined ignition timing. As shown in the drawing, when the air-fuel ratio is changed from the theoretical air-fuel ratio to a lean air-fuel ratio based on the optimal ignition timing, the amount of NOx emissions temporarily increased and reaches a maximum value at a slight lean air-fuel ratio (for example, 16.0), and thereafter decreases. Accordingly, if the third air-fuel ratio is set to a leaner air-fuel ratio (for example, 18.0) that the aforementioned slightly lean air-fuel ratio, the target air-fuel ratio changes from the first air-fuel ratio to the third air-fuel ratio in a manner that skips the air-fuel ratio region of the slightly lean air-fuel ratio at which the amount of NOx emissions becomes a maximum amount. It is thereby possible to change the actual air-fuel ratio in a manner that avoids the air-fuel ratio region in which an increase in the amount of NOx emissions becomes a problem, and hence the amount of NOx emissions can be effectively suppressed when switching the air-fuel ratio.

[0075]

However, after the virtual air-fuel ratio is switched from the first air-fuel ratio to the second air-fuel ratio, during a period in which the target air-fuel ratio is maintained at the first air- fuel ratio, a retardation amount of the ignition timing gradually increases accompanying an increase in the air amount. Accordingly, it is preferable to set the third air-fuel ratio to an optimal value by adaptation that takes into consideration the retardation limit of the ignition timing, the fuel consumption performance and the amount of NOx emissions.

[0076]

After the target air-fuel ratio is switched to the third air-fuel ratio, because the third air- fuel ratio is changed in a continuous manner to an air-fuel ratio that depends on the current air amount in accordance with the AF conversion map, the retardation amount of the ignition timing in the relevant period is suppressed and the fuel consumption performance improves. However, as shown in Fig. 4, when the ignition timing is retarded more the optimal ignition timing, the amount of NOx emissions decreases across the entire air-fuel ratio area due to a decrease in the combustion temperature. Accordingly, the AF conversion map that is used by the arithmetic unit 408 is set as a map that determines an air-fuel ratio that is necessary to achieve the requested first torque with the current estimated air amount under a condition in which the torque efficiency is made a somewhat lower value (for example, 80%). As a result, the amount of NOx emissions during the period in which the target air-fuel ratio is the third air-fuel ratio is suppressed.

[0077]

The above described series of processing operations that is executed by the arithmetic unit 408 can be represented by a flowchart illustrated in Fig. 5. The procedures by which the arithmetic unit 408 switches the target air-fuel ratio will be described again in accordance with this flowchart. Note that the series of processing operations illustrated in this flowchart is repeatedly executed at a predetermined operation cycle.

[0078]

In step SI of the flowchart in Fig. 5, the arithmetic unit 408 determines whether or not switching of the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio is completed. If the virtual air-fuel ratio is still the first air-fuel ratio, the processing of the arithmetic unit 408 advances to step S7. In step S7, processing to maintain the target air-fuel ratio at the first air-fuel ratio is performed. After step S7, the processing of the arithmetic unit 408 returns to step S I again. During this period, if the estimated torque is the value of the requested first torque, the ignition timing is the optimal ignition timing. If the virtual air-fuel ratio was switched to the second air-fuel ratio, the processing of the arithmetic unit 408 advances to step S2.

[0079]

When the virtual air-fuel ratio switches to the second air-fuel ratio, the estimated air amount increases towards the value of a target air amount corresponding to the second air-fuel ratio. In step S2, the arithmetic unit 408 determines whether or not the estimated air amount reached the intermediate air amount. If the estimated air amount has not reached the intermediate air amount, the processing of the arithmetic unit 408 advances to the above described step S7, in which processing to maintain the target air-fuel ratio at the first air-fuel ratio is performed. During this period, because the estimated torque is a larger value than the requested first torque, the ignition timing is retarded. On the other hand, if it is determined in step S2 that the estimated air amount reached the intermediate air amount, the processing of the arithmetic unit 408 advances to step S3.

[0080]

In step S3, the arithmetic unit 408 switches the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step manner. As a result, since the estimated air amount matches the intermediate air amount, and the estimated torque becomes the value of the requested first torque, the ignition timing becomes the optimal ignition timing. After step S3, the processing of the arithmetic unit 408 advances to step S4. In step S4, a target air-fuel ratio for achieving the requested first torque by means of the current estimated air amount is calculated based on the AF conversion map of the predetermined torque efficiency. Consequently, the ignition timing of this period is set as a retarded timing in accordance with the torque efficiency.

[0081]

After step S4, the processing of the arithmetic unit 408 advances to step S5. In step S5, the arithmetic unit 408 determines whether or not the estimated air amount has reached the target air amount. If it is determined as a result that the estimated air amount has not reached the target air amount, the processing of the arithmetic unit 408 returns to step S4.

[0082]

The arithmetic unit 408 repeatedly executes the processing of step S4 until the result determined in step S5 is affirmative. As a result, the target air-fuel ratio is changed in a continuous manner according to an increase in the estimated air amount, and the ignition timing of this period is set as a retarded timing in accordance with the torque efficiency. When the estimated air amount reaches the target air amount in due course, the processing of the arithmetic unit 408 advances to step S6. In step S6, the arithmetic unit 408 fixes the target air-fuel ratio at the second air-fuel ratio to thereby complete the switching of the target air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio.

[0083]

In the flowchart, first means of the present invention is realized by the arithmetic unit 408 executing the processing of steps S2 and S7, second means of the present invention is realized by the arithmetic unit 408 executing the processing of steps S2 and S3, third means of the present invention is realized by the arithmetic unit 408 executing the processing of steps S4 and S5, and fourth means of the present invention is realized by the arithmetic unit 408 executing the processing of steps S5 and S6.

[0084]

Returning again to Fig. 2, finally the arithmetic unit 410 will be described. The arithmetic unit 410 calculates the target second torque for switching. As described above, the target second torque for switching is inputted to the arithmetic unit 146 together with the requested second torque and the other second torque, and the smallest value among those values is selected by the arithmetic unit 146. The requested second torque and the other second torque are normally invalid values, and are switched to valid values only in a case where a special event has occurred. The same applies to the target second torque for switching also, and the arithmetic unit 410 normally sets the output value of the target second torque for switching to an invalid value.

[0085]

The requested first torque, the target air-fuel ratio, and the virtual air-fuel ratio are inputted to the arithmetic unit 410. According to the logic of the arithmetic units 404 and 408, the target air-fuel ratio and the virtual air-fuel ratio match before processing to switch the operation mode begins, and also match after the switching processing is completed. However, during the processing to switch the operation mode, a gap arises between the target air-fuel ratio and the virtual air-fuel ratio. The arithmetic unit 410 calculates the target second torque for switching that has a valid value, only during a period in which a gap arises between the target air- fuel ratio and the virtual air-fuel ratio. In this case, the requested first torque is used as the valid value of the target second torque for switching. That is, during a period in which a gap arises between the target air-fuel ratio and the virtual air-fuel ratio, the requested first torque is output from the arithmetic unit 410 as the target second torque for switching.

[0086]

The foregoing is a detailed description of the logic of the arithmetic unit 122, that is, the logic for switching the operation mode that is adopted in the present embodiment. Next, control results in a case where engine control is executed in accordance with the above described logic will be described using the drawings.

[0087]

Fig. 6 is a time chart that illustrates an image of results of control performed by the ECU according to the present embodiment. [0088]

In Fig. 6, a chart on a first tier illustrates changes over time in the torque. As described above, "TQlr" denotes the requested first torque, "TQ2c" denotes the target second torque for switching, and "TQe" denotes the estimated torque. Note that, in this case it is assumed that the requested first torque is the final target first torque, and the target second torque for switching is the final target second torque. Further, in addition to these torques, the actual torque is represented by a dashed line on the chart. However, the actual torque is not measured by the actual engine control. The line for the actual torque that is shown in the chart is an image line that is supported by test results.

[0089]

A chart on a second tier in Fig. 6 illustrates changes over time in the air amount. As described above, "KLt" denotes the target air amount, "KLe" denotes the estimated air amount, and "KLi" denotes the intermediate air amount. In addition to these air amounts, the actual air amount is also represented by a dashed line in the chart. However, the actual air amount is not measured by the actual engine control. The line for the actual air amount that is shown in the chart is an image line that is supported by test results.

[0090]

A chart on a third tier in Fig. 6 illustrates changes over time in the indicated ignition timing efficiency. As described above, "TU" denotes the indicated ignition timing efficiency.

[0091]

A chart on a fourth tier in Fig. 6 illustrates changes over time in the ignition timing. As described above, "SA" denotes the ignition timing. The retardation limit of the ignition timing is represented by a chain double-dashed line in the chart.

[0092]

A chart on a fifth tier in Fig. 6 illustrates changes over time in the air-fuel ratio. As described above, "AFt" denotes the target air-fuel ratio, and "AFh" denotes the virtual air-fuel ratio. Further, "AF1" denotes the first air-fuel ratio, "AF2" denotes the second air-fuel ratio and "AF3" denotes the third air-fuel ratio. A chart on a sixth tier in Fig. 6 illustrates changes over time in the actual air-fuel ratio.

[0093]

Results of control according to the target air-fuel ratio switching logic adopted in the present embodiment will now be described based on Fig. 6. At a time of deceleration, the target air-fuel ratio and the virtual air-fuel ratio are each maintained at the first air-fuel ratio that is the theoretical air-fuel ratio until the requested first torque decreases to the level of the reference value that is represented by "Ref in Fig. 6. Hence, the target air amount that is calculated based on the requested first torque and the virtual air-fuel ratio decrease in response to a decrease in the requested first torque. During this period, the target second torque for switching is set to an invalid value in response to the target air-fuel ratio and the virtual air-fuel ratio matching. Since the indicated ignition timing efficiency becomes 1 when the target second torque for switching is an invalid value, the ignition timing is maintained at the optimal ignition timing. Note that, although the ignition timing in the chart changes in accordance with a decrease in the requested first torque, this is a change that corresponds to the optimal ignition timing changing depending on the engine speed or the air amount.

[0094]

When the requested first torque becomes lower than the reference value, only the virtual air-fuel ratio is switched from the first air-fuel ratio to the second air-fuel ratio. That is, although the target air-fuel ratio is maintained at the first air-fuel ratio that is the theoretical air- fuel ratio, the virtual air-fuel ratio is made leaner in a step manner. Operation according to the second air-fuel ratio that is a lean air-fuel ratio requires a larger air amount than the air amount required for operation according to the first air-fuel ratio that is the theoretical air-fuel ratio. Therefore, when the virtual air-fuel ratio that is used for calculating the target air amount is switched in a step manner to the second air-fuel ratio, the target air amount also increases in a step manner at the time point of such switching. However, because there is a response delay until the actuator operates and the air amount changes, the actual air amount and the estimated air amount that is an estimated value thereof do not increase in a step manner, and increase at a delayed time relative to the target air amount.

[0095]

During a period from when the requested first torque becomes lower than the reference value and a divergence arises between the target air-fuel ratio and the virtual air-fuel ratio until the target air-fuel ratio and the virtual air-fuel ratio match again, the target second torque for switching is set to the same value as the requested first torque that is a valid value. On the other hand, during a period in which the target air-fuel ratio is maintained at the first air-fuel ratio, the estimated torque that is calculated based on the estimated air amount and the target air-fuel ratio gradually increases relative to the requested first torque accompanying an increase in the estimated air amount that is caused by switching of the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio. As a result of the estimated torque changing in this manner relative to the requested first torque, the indicated ignition timing efficiency that is the proportion of the target second torque for switching relative to the estimated torque decreases monotonously.

[0096]

The indicated ignition timing efficiency determines the ignition timing. The smaller that the value of the indicated ignition timing efficiency is, the greater that the retardation amount with respect to the optimal ignition timing of the ignition timing becomes. From the time that the virtual air-fuel ratio is switched from the first air-fuel ratio to the second air-fuel ratio onwards, the ignition timing is retarded monotonously in response to a decrease in the indicated ignition timing efficiency.

[0097]

The actual air amount and the estimated air amount arrive at the intermediate air amount in due course. At that time point, the target air-fuel ratio is rapidly switched from the first air- fuel ratio to the third air-fuel ratio. At this time, the target air-fuel ratio changes in a step manner, and not in a continuous manner. It is thereby possible to change the actual air-fuel ratio in a manner that skips an air-fuel ratio region in which the amount of NOx emissions increases.

[0098]

When the target air-fuel ratio is being switched to the third air-fuel ratio, the target air- fuel ratio is switched in a continuous manner to a value for achieving the requested first torque by means of the current estimated air amount and the predetermined torque efficiency. The value of the predetermined torque efficiency is a value that is set from the viewpoint of suppressing the amount of NOx emissions. From the time that the target air-fuel ratio is switched to the third air-fuel ratio onwards, the estimated torque becomes a value that is larger than the requested first torque accompanying the estimated air amount being raised by an amount corresponding to the predetermined torque efficiency. As a result of the estimated torque becoming a large value relative to the requested first torque, the indicated ignition timing efficiency that is the proportion of the target second torque for switching relative to the estimated torque becomes a value that is less than 1. Consequently, the ignition timing is retarded in response to the decrease in the indicated ignition timing efficiency.

[0099] When the estimated air amount converges on the target air amount, and a difference between the target air amount and the estimated air amount becomes equal to or less than a threshold value, the target air-fuel ratio is fixed at the second air-fuel ratio. As a result, switching of the operation mode from the stoichiometric mode to the lean mode ends. Further, the target second torque for switching is returned to an invalid value in response to the target air- fuel ratio and the virtual air-fuel ratio matching each other. As a result, the indicated ignition timing efficiency is returned to 1 , and the ignition timing is returned again to the optimal ignition timing.

[0100]

First, as a comparative example, a case will be considered in which the target air-fuel ratio is changed in a step manner from the third air-fuel ratio to the second air-fuel ratio. During a period in which the target air-fuel ratio is being maintained at the third air-fuel ratio, the estimated torque gradually increases relative to the requested first torque accompanying an increase in the estimated air amount. As a result, a retardation amount of the ignition timing gradually increases in response to a decrease in the indicated ignition timing efficiency. When the retardation amount of the ignition timing increases in this manner, it leads to a deterioration in the fuel consumption. Further, a retardation limit is set with respect to the ignition timing, and it is not permitted to retard the ignition timing beyond the retardation limit. Consequently, an increase in the torque caused by an excessive air amount cannot be cancelled out adequately by retarding the ignition timing.

[0101]

In contrast, according to the logic adopted in the present embodiment, during a period in which the target air-fuel ratio is fixed to the third air-fuel ratio, the retardation amount of the ignition timing is not monotonously increased in a continuous manner, but rather the retardation amount of the ignition timing is suppressed by changing the third air-fuel ratio in a continuous manner. According to this logic, during a period in which the target air-fuel ratio is changing in a continuous manner towards the second air-fuel ratio from the third air-fuel ratio, the emitted amount of NOx is suppressed and, furthermore, a deterioration in the fuel consumption is also suppressed.

[0102]

As described above, according to the logic adopted in the present embodiment, when switching from operation according to the first air-fuel ratio to operation according to the second air-fuel ratio, the air-fuel ratio is changed in a step manner that skips an air-fuel ratio region in which the amount of NOx emissions increases, and thereafter the changing of the actual air-fuel ratio in a continuous manner in accordance with the air response. It is thereby possible to switch the air-fuel ratio in a manner that suppresses fluctuations in the torque, and also suppress a deterioration in the fuel consumption performance and a deterioration in the NOx emissions performance at the time of switching.

[0103]

[Other Embodiments]

The present invention is not limited to the above described embodiment, and various modifications can be made without departing from the spirit and scope of the present invention. For example, the modifications described hereunder may also be adopted.

[0104]

Although according to the logic adopted in the present embodiment the arithmetic unit 408 calculates the target air-fuel ratio as the third air-fuel ratio using the AF conversion map, a compensation for not exceeding an allowable limit of the amount of NOx emissions may also be incorporated into the relevant calculation. The computational procedure thereof is described hereunder with reference to Fig. 7. Fig. 7 is a view illustrating the relation of the amount of NOx emissions with respect to the air-fuel ratio. First, the arithmetic unit 408 calculates a target air- fuel ratio for achieving the requested first torque by means of the current estimation air amount based on the AF conversion map for a predetermined torque efficiency (for example 80%). Next, using the relation illustrated in Fig. 7, the arithmetic unit 408 calculates the amount of NOx emissions corresponding to the calculated target air-fuel ratio. If the amount of NOx emissions does not exceed a predetermined allowable limit, the arithmetic unit 408 uses the target air-fuel ratio calculated based on the AF conversion map as the target air-fuel ratio in the current step. On the other hand, if the amount of NOx emissions exceeds the predetermined allowable limit, the arithmetic unit 408 uses the value of the target air-fuel ratio in the previous step as the current target air-fuel ratio. As a result, the amount of NOx emissions is suppressed to an amount that is equal to or less than the allowable limit during a period in which the target air-fuel ratio is the third air-fuel ratio.

[0105]

According to the logic adopted in the present embodiment, in response to the requested first torque becoming lower than the reference value, the arithmetic unit 404 switches the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio. However, the method of switching the virtual air-fuel ratio is not limited thereto, and a method may also be adopted in which the virtual air-fuel ratio is caused to pass through the third air-fuel ratio when switching the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio. More specifically, during a period in which the requested first torque is greater than the reference value, the arithmetic unit 404 sets the virtual air-fuel ratio to the first air-fuel ratio in response to the requested first torque becoming greater than the reference value. When the requested first torque decreases and eventually becomes lower than the reference value, the arithmetic unit 404 switches the virtual air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in response to the requested first torque decreasing to a value that is equal to or less than the reference value. Thereafter, the arithmetic unit 404 performs a comparison between the intermediate air amount and the estimated air amount for each series of control operations executed by the arithmetic unit 404. Subsequently, upon the estimated air amount arriving at the intermediate air amount, the arithmetic unit 404 rapidly changes the virtual air-fuel ratio from the third air-fuel ratio to the second air-fuel ratio at that time point.

[0106]

Upon detecting that the virtual air-fuel ratio that is inputted from the arithmetic unit 404 has been switched from the first air-fuel ratio to the third air-fuel ratio, the arithmetic unit 408 performs a comparison between the intermediate air amount and the estimated air amount for each series of control operations executed by the arithmetic unit 408. Immediately after the virtual air-fuel ratio is switched from the first air-fuel ratio to the third air-fuel ratio, the estimated air amount is a smaller value than the intermediate air amount. Further, since the estimated torque is a larger value than the requested first torque, the indicated ignition timing efficiency becomes a value that is less than 1 , and retardation of the ignition timing is performed. Upon the estimated air amount arriving at the intermediate air amount in due course, the arithmetic unit 408 rapidly switches the target air-fuel ratio from the first air-fuel ratio to the third air-fuel ratio in a step maimer at that time point. As a result, the target air-fuel ratio changes in a manner that skips the air- fuel ratio region of a slightly lean air-fuel ratio at which the amount of NOx emissions is largest. Since it is thereby possible to change the actual air-fuel ratio in a manner that avoids an air-fuel ratio region in which an increase in the emitted amount of NOx is a problem, the emitted amount of NOx when switching the air-fuel ratio is effectively suppressed.

[0107] Further, when the estimated air amount arrives at the intermediate air amount, the virtual air-fuel ratio is switched from the third air-fuel ratio to the second air-fuel ratio, and the target air- fuel ratio is changed in a continuous manner to an air-fuel ratio that is in accordance with the current air amount. Consequently, the air amount is changed towards a target air amount that corresponds to the second air-fuel ratio while suppressing the retardation amount of the ignition timing. Thus, even when the virtual air-fuel ratio passes through the third air-fuel ratio when being switched from the first air-fuel ratio to the second air-fuel ratio at the time of switching the operation mode from the stoichiometric mode to the lean mode, a deterioration in the fuel consumption performance and a deterioration in the NOx emissions performance can be suppressed in a similar manner as when directly switching the virtual air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio.

[0108]

An engine that is taken as a control object according to the present embodiment is not limited to a lean-burn engine with a turbocharger, and may be a lean-burn engine in which a turbocharger is not installed. Note that, in a case where the engine that is taken as a control object according to the present embodiment is a lean-burn engine with a turbocharger, and which includes a supercharging property varying actuator that changes a supercharging property of the turbocharger, such as a waste gate valve (hereunder, referred to as "WGV"), the following control relating to the WGV may also be performed.

[0109]

Fig. 8 illustrates settings of operating ranges according to the present embodiment. The operating ranges are defined by the intake pipe pressure and the engine speed. The settings of the operating ranges as shown in Fig. 8 are mapped and stored in the ECU. The ECU executes switching of the operation mode in accordance with the map. According to Fig. 8, a lean mode region in which the lean mode is selected is set in a low-to-medium speed and low-to-medium load region. Based on Fig. 8, it is found that a region in which the lean mode is selected also exists in a supercharging region in which the intake pipe pressure becomes higher than the atmospheric pressure. That is, when switching the operation mode, switching of the operation mode from the stoichiometric mode in a supercharging region to the lean mode in a

supercharging region is performed in some cases. If the WGV is placed in a temporarily open state in this case, the necessity arises to rise again the supercharging pressure that temporarily fell and to realize an air amount corresponding to the lean mode in the supercharging region, and the time required for switching the operation mode becomes a prolonged period.

[0110]

Therefore, according to a modification of the present embodiment, in a case where it is determined based on the manner in which the requested first torque decreases that switching of the operation mode from the stoichiometric mode in the supercharging region to the lean mode in the supercharging region is performed, control is performed that keeps the WGV closed. As a result, since the air responsiveness can be raised, the time required to switch the operation mode can be effectively shortened. Further, if a configuration is adopted that closes the WGV while switching the operation mode, the internal EGR rate increases as the result of the back pressure rising. It is thereby possible to effectively suppress the amount of NOx emissions when switching the operation mode. Note that, a duty ratio of a solenoid that drives the WGV, and not the degree of opening of the WGV, may also be adopted as the operation amount of the WGV.

[01 1 1]

Although the third air-fuel ratio is described as 18.0 in the embodiment, as long as the air- fuel ratio is leaner than an air-fuel ratio (for example, 16.0) at which the amount of NOx emissions is largest, the third air-fuel ratio may be set to an arbitrary optimal value that takes into account the exhaust performance (amount of NOx emissions) and the fuel consumption performance (ignition timing retardation amount).

[0112]

Switching of the operation mode that is executed according to the logic adopted in the present embodiment is not limited to switching from the stoichiometric mode to the lean mode when decelerating, and can also be applied to switching from the stoichiometric mode to the lean mode when accelerating, for example, when switching the operation mode at a time of acceleration from an idling operation.

[01 13]

The air-fuel ratio (virtual air-fuel ratio) that is used for calculating a target air amount in the embodiment can be replaced with an equivalence ratio. The equivalence ratio is also a parameter that provides a conversion efficiency of the air amount to torque, and corresponds to a parameter that corresponds to the air-fuel ratio. Likewise, an excess air factor can be used as a parameter that provides a conversion efficiency of the air amount to torque.

[0114] A variable lift amount mechanism that makes a lift amount of the intake valve variable can also be used as a first actuator that changes the amount of air drawn into the cylinders. The variable lift amount mechanism can be used independently instead of the throttle, or can be used in combination with another first actuator such as the throttle or VVT. The VVT may also be omitted.

[0115]

A variable nozzle can also be used as a supercharging property varying actuator that changes a supercharging property of the turbocharger. Further, if the turbocharger is assisted by an electric motor, the electric motor can also be used as a supercharging property varying actuator.

[0116]

In the embodiment of the present invention, an injector as the second actuator is not limited to a port injector. An in-cylinder injector that injects fuel directly into the combustion chamber can also be used, and both a port injector and an in-cylinder injector may also be used in combination.

[01 17]

The first air-fuel ratio is not limited to the theoretical air-fuel ratio. The first air-fuel ratio can also be set to an air-fuel ratio that is leaner than the theoretical air-fuel ratio, and an air- fuel ratio that is leaner than the first air-fuel ratio can be set as the second air-fuel ratio.

Reference Signs List

[01 18]

2 THROTTLE

4 INJECTOR

6 IGNITION DEVICE

8 VARIABLE VALVE TIMING MECHANISM

100 ENGINE CONTROLLER

101 INTERFACE AS REQUESTED TORQUE RECEPTION MEANS

200 POWERTRAIN MANAGER

162 ARITHMETIC UNIT AS TARGET AIR AMOUNT CALCULATION MEANS

164, 166, 178 ARITHMETIC UNIT AS FIRST ACTUATOR CONTROL MEANS

174, 176 ARITHMETIC UNIT AS SECOND ACTUATOR CONTROL MEANS

168, 170, 172 ARITHMETIC UNIT AS THIRD ACTUATOR CONTROL MEANS 404 ARITHMETIC UNIT AS PARAMETER VALUE CHANGING MEANS

406, 408 ARITHMETIC UNIT AS TARGET AIR-FUEL RATIO SWITCHING MEANS