JP2015197096A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve exhaust emission while keeping fuel economy and responsiveness satisfactorily even in a case of acceleration during a boosting lean combustion mode.SOLUTION: An ECU 50 switchably executes a stoichiometric combustion mode of burning an air-fuel mixture at a stoichiometric air-fuel ratio and a boosting lean combustion mode of firing the air-fuel mixture at a lean air-fuel ratio in a state of boosting a pressure by a turbocharger 34. Furthermore, if there is a request to increase an output torque during the execution of the boosting lean combustion mode, the ECU 50 calculates a first lean injection quantity A for realizing a target torque and optimizing fuel economy and a second lean injection quantity B for making the air-fuel ratio match the lean air-fuel ratio based on an actual air quantity, and sets a final fuel injection quantity F to a value between the lean injection quantities A and B. As a result, in a case of increasing the output torque in the boosting lean combustion mode, it is possible to keep high responsiveness and, at the same time, improve exhaust emission while maintaining fuel economy.

Description

  The present invention relates to a control device for an internal combustion engine provided with a supercharger.

  As a conventional technique, for example, as disclosed in Japanese Patent Application Laid-Open No. 7-27003, a control device for an internal combustion engine that controls an air-fuel ratio is known. In the prior art, for example, when the air-fuel ratio is changed from the lean air-fuel ratio to the stoichiometric air-fuel ratio, the air-fuel ratio between the lean air-fuel ratio and the stoichiometric air-fuel ratio is first maintained for a predetermined time, and then the stoichiometric air-fuel ratio is changed. The configuration is realized.

JP-A-7-27003

  By the way, in a supercharged engine or the like, there is a case where combustion control is performed at a lean air-fuel ratio while performing a supercharging operation in a specific operation mode (supercharging lean combustion mode). As a method for increasing the output torque in the supercharged lean combustion mode, the following two methods are conceivable. First, the first method is to increase the actual air amount by increasing the throttle opening in accordance with the operation of the driver, and increase the fuel injection amount following the increase in the actual air amount. . However, in this method, a response delay such as a turbo lag is likely to occur, and the responsiveness to the driving operation may be reduced.

  In the second method, the fuel injection amount is first increased in accordance with the operation of the driver, and the actual air amount is increased following the increase in the fuel injection amount. In this method, for example, the fuel injection amount can be set based on the optimum air-fuel ratio set according to the operating state, so that the output torque can be increased with good responsiveness while maintaining good fuel efficiency. However, in the second method, since there is a period in which the fuel injection amount increases prior to the actual air amount, the air-fuel ratio is disturbed in this period and the like, and there is a possibility that the exhaust emission is reduced.

  For this reason, in the prior art, when the output torque is increased during the supercharged lean combustion mode, there is a problem that it is difficult to improve the exhaust emission while maintaining good fuel efficiency and responsiveness.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to maintain an excellent fuel economy and responsiveness even when accelerating during a supercharged lean combustion mode. An object of the present invention is to provide a control device for an internal combustion engine that can improve emissions.

A first invention is a supercharger that supercharges intake air;
A stoichiometric combustion mode in which an air-fuel mixture corresponding to the stoichiometric air-fuel ratio is combusted, and a supercharged lean combustion mode in which the air-fuel mixture having a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio is burned in a state of being supercharged by the supercharger. Combustion switching means for switching the combustion mode between the stoichiometric combustion mode and the supercharged lean combustion mode,
When a request to increase the output torque occurs during execution of the supercharged lean combustion mode, the fuel injection amount is increased following the increase in the actual air amount while increasing the actual air amount based on the input of the target torque. A first injection amount that achieves the target torque and optimizes fuel consumption; and a second injection amount that causes the air-fuel ratio to coincide with the lean air-fuel ratio based on an actual air amount. And an injection amount setting means for setting the final fuel injection amount to a value between the first injection amount and the second injection amount.

  According to the first aspect of the invention, it is possible to maintain the exhaust emission better than in the case where only the responsiveness of the internal combustion engine is emphasized, and to improve the responsiveness compared to the case where only the exhaust emission is emphasized. In this state, the output torque can be increased. Therefore, in the case where the output torque is increased during the supercharged lean combustion mode, both responsiveness and exhaust emission can be achieved while maintaining fuel efficiency.

It is a block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a control block diagram which shows the injection quantity setting control performed in the supercharging lean combustion mode. In Embodiment 1 of this invention, it is a flowchart which shows an example of the control performed by ECU. It is a timing chart which shows the behavior of each parameter of an engine at the time of performing injection amount setting control.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system according to the present embodiment includes an engine 10 that is an internal combustion engine with a supercharger. In FIG. 1, only one cylinder of the engine 10 is illustrated. The piston 12 provided in the cylinder of the engine 10 is connected to the crankshaft 14 and forms a combustion chamber 16 in the cylinder. Further, the engine 10 discharges exhaust gas in the combustion chamber 16, an intake passage 18 that sucks air into the combustion chamber 16, an electronically controlled throttle valve 20 that adjusts the amount of intake air flowing through the intake passage 18. An exhaust passage 22 and a catalyst 24 for purifying exhaust gas are provided. The catalyst 24 includes a NOx catalyst that occludes and reduces NOx, a three-way catalyst, and the like.

  Each cylinder of the engine 10 includes a fuel injection valve 26 that injects fuel into the intake passage 18, an ignition plug 28, an intake valve 30, an exhaust valve 32, and the like. The engine 10 is equipped with a supercharger 34 that supercharges intake air using exhaust pressure. The supercharger 34 is constituted by a turbine 34 a provided in the exhaust passage 22 and a compressor 34 b provided in the intake passage 18. The exhaust passage 22 is provided with a waste gate valve (WGV) 36 that allows the exhaust gas to flow by bypassing the turbine 34a.

  The system of the present embodiment includes a sensor system that detects the operating state of the engine 10 and an ECU (Electronic Control Unit) 50 that controls the engine 10 based on the output of the sensor system. The sensor system includes a crank angle sensor 40 that outputs a signal for detecting the engine speed (engine speed) and a crank angle, an air flow sensor 42 that detects an intake air amount, and an air-fuel ratio that detects an exhaust air-fuel ratio. The sensor 44 is configured. The ECU 50 calculates the intake air amount (actual air amount), the engine speed, the engine load, and the like based on the output of the sensor system, and the throttle valve 20, the fuel injection valve 26, the spark plug 28, An actuator such as the WGV 36 is driven. Thereby, the ECU 50 can control the operating state of the engine 10 while burning the air-fuel mixture in the combustion chamber 16 (inside the cylinder). Further, the ECU 50 executes combustion switching control and injection amount setting control described below.

[Features of Embodiment 1]
The combustion switching control switches the combustion mode of the air-fuel mixture based on the operating state of the engine 10, and this combustion mode includes at least a stoichiometric combustion mode and a supercharging lean combustion mode. The stoichiometric combustion mode is a mode in which an air-fuel mixture having a stoichiometric air-fuel ratio (stoichiometric) or an air-fuel ratio close thereto is generated and the air-fuel mixture is combusted. The supercharged lean combustion mode is a mode in which the air-fuel mixture having a lean air-fuel ratio that is a leaner air-fuel ratio than the stoichiometric air-fuel ratio is generated in a state in which the intake air is supercharged by the supercharger 34, and the air-fuel mixture is combusted. It is.

  Next, the injection amount setting control executed during the supercharging lean combustion mode will be described. FIG. 2 is a control block diagram showing injection amount setting control. In this figure, “TQ” and “KL” represent “torque” and “load (engine load)”, respectively. The injection amount setting control calculates the first and second lean injection amounts A and B based on the target torque input according to the driver's accelerator operation or the like, and based on these lean injection amounts A and B. The final fuel injection amount is set. The lean injection amounts A and B correspond to the first and second injection amounts.

  Specifically, in the process of calculating the first lean injection amount A, as shown in the upper side of FIG. 2, first, the stoichiometric demand load corresponding to the demand load in the stoichiometric state is calculated based on the target torque. calculate. Since the air-fuel ratio in the stoichiometric state can be regarded as a constant value (= theoretical air-fuel ratio), the stoichiometric demand load can be obtained without using a data map or the like. Next, the first lean injection amount A is calculated by calculating the stoichiometric injection amount based on the stoichiometric demand load and performing a predetermined lean correction on the calculated value of the stoichiometric injection amount. As a specific example of the leaning correction, there is a method of multiplying the stoichiometric injection amount by a correction coefficient (for example, 0.9) smaller than 1.

  The first lean injection amount A calculated in this manner is obtained by multiplying the stoichiometric injection amount obtained from the target load in the stoichiometric state by the fuel efficiency improvement rate in the lean state. That is, the first lean injection amount A is an injection amount that optimizes fuel efficiency while realizing the target torque and ensuring the response of the engine 10. In the above calculation process, for example, setting the correction coefficient for leaning correction to 0.9 corresponds to setting the fuel efficiency improvement rate to 10%. In the present invention, if necessary, the correction coefficient may be set to a value other than 0.9.

  On the other hand, in the process of calculating the second lean injection amount B, as shown on the lower side in FIG. 2, first, a lean required load corresponding to the required load in the lean state is calculated based on the target torque. Subsequently, the actual load is detected based on the output of the sensor system in a state where the actuator is driven so that the actual load matches the lean required load. Then, the second lean injection amount B is calculated by dividing the actual load by the target A / F.

  As the actuator, for example, a throttle actuator (TA) that changes the opening of the throttle valve 20, a VVT that changes the valve timing, a WGV 36 that changes the supercharging pressure, or the like can be used. As a result, the second lean injection amount B is an injection amount that improves the exhaust emission by matching the actual air-fuel ratio with the lean air-fuel ratio based on the actual intake air amount (actual air amount). Further, the second lean injection amount B is smaller than the first lean injection amount A (A> B) as shown in FIG. 4 described later.

  Next, in the injection amount setting control, when there is a request to increase the output torque during the supercharging lean combustion mode, the final fuel injection amount F is changed to the first lean injection amount A and the second lean injection amount B. Set to a value between. That is, the final fuel injection amount F is set so that these three injection amounts A, B, and F satisfy the magnitude relationship of A ≧ F ≧ B.

  Therefore, according to the injection amount setting control, when the actual air amount is increased based on the input of the target torque and the fuel injection amount is increased following the increase in the actual air amount, the fuel injection amount F is made lean. A value between the injection amounts A and B can be set. Thereby, the exhaust emission can be favorably maintained while improving the responsiveness and fuel consumption of the engine 10.

  Further, when performing the above-described injection amount setting control, (1) whether it is a lean region, (2) whether it is a supercharging region, or (3) whether there is a margin in the purification capacity of the NOx catalyst. It may be configured to switch whether or not to execute the injection amount setting control based on the above conditions. A specific example of this configuration will be described with reference to FIG.

[Specific Processing for Realizing Embodiment 1]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 3 is a flowchart showing an example of the control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed while the engine 10 is in operation. In the routine shown in FIG. 3, first, in step 100, it is determined based on the output of the air-fuel ratio sensor 44 or the like whether or not the current operation region is a lean region. If the determination in step 100 is established, the process proceeds to step 102. If the determination in step 100 is not established, the process proceeds to step 112 described later.

  Next, in step 102, it is determined whether or not the vehicle is accelerating (when a request to increase the output torque is generated). Determine whether or not. Note that the determination process in step 102 is performed based on a change in the accelerator opening, a state where the required torque has not been achieved, or the like. If the determinations in steps 102 and 104 are both established, the process proceeds to step 106. On the other hand, if the determination is not established in any of steps 102 and 104, the process proceeds to step 110 described later.

  Next, in step 106, it is determined whether or not there is a margin in the purification capacity of the NOx catalyst. This determination process may be executed based on whether or not the catalyst 24 has been warmed up. Specifically, in step 106, for example, when the NOx counter that counts the amount of NOx stored in the NOx catalyst as a numerical value is equal to or lower than the reference value, and the temperature (bed temperature) of the catalyst 24 is equal to or higher than the reference temperature. In addition, it may be configured that the determination in step 106 is deemed to have been established. If the determination in step 106 is established, the process proceeds to step 108, and if the determination in step 106 is not established, the process proceeds to step 112.

  Next, in step 108, an average value of the first and second lean injection amounts A and B is calculated, and this average value is set as a final fuel injection amount F (F = (A + B) / 2). . As a result, in step 108, the fuel injection amount F is changed to the first lean injection amount A and the second lean injection amount B when it is executed in the lean region and the supercharging region and at the time of acceleration. Can be set to a value between. In particular, in the supercharging region, when lean combustion is performed, turbo lag is likely to occur due to low exhaust energy. For this reason, in step 108, the fuel injection amount F can be set to a value between the lean injection amounts A and B to suppress the turbo lag. In step 108, the fuel injection amount F is set to the average value of the lean injection amounts A and B. However, the present invention is not limited to this, and the fuel injection amount F includes the lean injection amount A and the lean injection amount. If the value is set to a value between B, various other setting methods may be used.

  Further, in step 110, the final fuel injection amount F is set to the second lean injection amount B when it is not during acceleration and when it is not in the supercharging region. In these cases, since a rich air-fuel mixture is not required, the exhaust emission can be maintained satisfactorily by using the second lean injection amount B.

  In step 112, the final fuel injection amount F is set to the stoichiometric injection amount when it is not in the lean region and when there is no margin in the purification capacity of the NOx catalyst. The stoichiometric injection amount is calculated as a stoichiometric injection amount for maintaining the air-fuel ratio at stoichiometric. In step 112, the final fuel injection amount F may be set by any one of the first and second methods described below. The first method is a method in which the actual air amount is increased by increasing the throttle opening in accordance with the operation of the driver, and the fuel injection amount is increased following the increase in the actual air amount. In the second method, the fuel injection amount is first increased in accordance with the operation of the driver, and the actual air amount is increased following the increase in the fuel injection amount. In the present embodiment, steps 100 to 106 in FIG. 3 show a specific example of the combustion switching means, and steps 108 to 112 show a specific example of the injection amount setting means.

  Next, the effect of the injection amount setting control will be described with reference to FIG. FIG. 4 is a timing chart showing the behavior of each parameter of the engine when the injection amount setting control is executed. In this figure, a thick line indicates a characteristic line when the final fuel injection amount F is an average value of the lean injection amounts A and B, and a thin line indicates a case where the fuel injection amount F is set to the lean injection amount A. A characteristic line is shown. A dotted line indicates a characteristic line when the fuel injection amount F is set to the lean injection amount B.

  First, as indicated by a thin line in FIG. 4, when a vehicle or driver's acceleration request is generated, the target torque is abruptly increased with an emphasis on the responsiveness of the engine 10, and the lean injection amount is set as the fuel injection amount F. When A is used, the supercharging pressure and the fuel injection amount rapidly increase accordingly. As a result, the air-fuel ratio changes greatly from the stoichiometric side to the rich side, so that the NOx emission amount of the engine 10 increases and the increasing speed of the NOx counter value increases. Further, as shown by a dotted line in FIG. 4, when the target torque is gradually increased with emphasis on exhaust emission and the lean injection amount B is used as the fuel injection amount F, the supercharging pressure and the fuel injection amount The increase will also be relatively moderate. As a result, since the air-fuel ratio is maintained at a value close to the stoichiometric value, the NOx emission amount of the engine 10 is equivalent to that in the steady state, and NOx emission is suppressed.

  On the other hand, in the present embodiment, the fuel injection amount F is set to the average value of the lean injection amounts A and B while increasing the target torque moderately to some extent with respect to the acceleration request. As indicated by the thick line, the supercharging pressure and the fuel injection amount can be appropriately reduced to prevent the air-fuel ratio from changing greatly to the rich side. Thereby, exhaust emission can be discharged well while ensuring the responsiveness of the engine 10.

  That is, according to the present embodiment, based on the first lean injection amount A and the actual air amount that are required when the target torque is output in a state where the fuel efficiency is optimized while placing importance on the responsiveness of the engine 10. The final fuel injection amount is a value between the lean injection amount A and the lean injection amount B on the basis of the second lean injection amount B necessary for controlling the air-fuel ratio to a preset lean air-fuel ratio. Can be set to As a result, the exhaust emission can be maintained better than when only the responsiveness is emphasized, and the responsiveness can be improved compared with the case where only the exhaust emission is emphasized. Can be increased. Therefore, in the case where the output torque is increased during the supercharged lean combustion mode, both responsiveness and exhaust emission can be achieved while maintaining fuel efficiency.

10 Engine (Internal combustion engine)
12 Piston 16 Combustion chamber 18 Intake passage 20 Throttle valve 22 Exhaust passage 26 Fuel injection valve 34 Supercharger 36 Waste gate valve 40 Crank angle sensor 42 Air flow sensor 44 Air fuel ratio sensor 50 ECU

Claims (1)

A supercharger for supercharging the intake air;
A stoichiometric combustion mode in which an air-fuel mixture corresponding to the stoichiometric air-fuel ratio is combusted, and a supercharged lean combustion mode in which the air-fuel mixture having a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio is burned in a state of being supercharged by the supercharger. Combustion switching means for switching the combustion mode between the stoichiometric combustion mode and the supercharged lean combustion mode,
When a request to increase the output torque occurs during execution of the supercharged lean combustion mode, the fuel injection amount is increased following the increase in the actual air amount while increasing the actual air amount based on the input of the target torque. A first injection amount that achieves the target torque and optimizes fuel consumption; and a second injection amount that causes the air-fuel ratio to coincide with the lean air-fuel ratio based on an actual air amount. An injection amount setting means for setting a final fuel injection amount to a value between the first injection amount and the second injection amount;
The control apparatus of the internal combustion engine provided with.

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