Fuel injection amount control device

Abstract

To provide a fuel injection quantity control device which can properly increase fuel injection quantity while suppressing a rich misfire.SOLUTION: A fuel injection quantity control device comprises: a target fuel injection quantity calculation unit that calculates a target fuel injection quantity by correcting a fundamental fuel injection quantity calculated according to an operation state of an internal combustion engine so as to increase the fundamental fuel injection quantity; a total incremental quantity calculation unit that calculates a total incremental quantity, the total incremental quantity being a total of an equivalence ratio incremental quantity being an incremental correction quantity for controlling an equivalence ratio of an air-fuel mixture at a target equivalence ratio, and a non-contribution incremental quantity being an incremental correction quantity for compensating for a fuel quantity which does not contribute to combustion; and an upper limit value calculation unit that calculates an upper limit value of an incremental correction on the basis of the operation state of the internal combustion engine and a temperature of cooling water. When the total incremental quantity is smaller than the upper limit value, the target fuel injection quantity is calculated by adding the total incremental quantity to the fundamental fuel injection quantity. When the total incremental quantity is equal to or larger than the upper limit value, the target fuel injection quantity is calculated by adding the upper limit value to the fundamental fuel injection quantity.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel injection amount control device. [Background technology]

[0002] It is known to calculate a target fuel injection amount by correcting a basic fuel injection amount calculated in accordance with the operating state of an internal combustion engine so as to increase the amount (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-218582 A [Patent Document 2] JP 2015-143482 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, it is conceivable to correct the basic fuel injection amount by increasing it so that the equivalence ratio of the mixture becomes the target equivalence ratio. On the other hand, since a part of the injected fuel adheres to the wall surface inside the cylinder and does not contribute to combustion, it is conceivable to correct the basic fuel injection amount by increasing it in order to compensate for such a fuel portion that does not contribute to combustion. Therefore, it is conceivable to calculate the target fuel injection amount by adding the above two increase correction amounts to the basic fuel injection amount. However, in this case, the actual fuel injection amount may become excessive, which may cause a rich misfire.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a fuel injection amount control device that can appropriately increase the fuel injection amount while suppressing rich misfires. [Means for solving the problem]

[0006] The above object is to provide an internal combustion engine having an internal combustion engine with a target fuel injection amount calculation unit that calculates a target fuel injection amount by correcting a basic fuel injection amount calculated in accordance with an operating state of the internal combustion engine so as to increase it, a total increase amount calculation unit that calculates a total increase amount that is the sum of an equivalence ratio increase amount that is an increase correction amount for controlling an equivalence ratio of an air-fuel mixture to a target equivalence ratio, and a non-contributing fuel increase amount that is an increase correction amount for compensating for a fuel amount that does not contribute to combustion, and an upper limit value calculation unit that calculates an upper limit value of the increase correction based on an operating state of the internal combustion engine and a temperature of cooling water of the internal combustion engine, wherein the target fuel injection amount calculation unit calculates the target fuel injection amount by adding the total increase amount to the basic fuel injection amount when the total increase amount is less than the upper limit value, and calculates the target fuel injection amount by adding the upper limit value instead of the total increase amount when the total increase amount is equal to or greater than the upper limit value. the total increase calculation unit calculates the total increase by multiplying the basic fuel injection amount by an increase correction coefficient, the increase correction coefficient being calculated by adding an equivalence ratio correction coefficient, which is a correction coefficient for increasing the basic fuel injection amount so as to compensate for a fuel amount that does not contribute to combustion, to an equivalence ratio correction coefficient, which is a correction coefficient for increasing the basic fuel injection amount so as to make up for a fuel amount that does not contribute to combustion, and further subtracting 1 from the sum; when a detected air-fuel ratio of a downstream air-fuel ratio sensor disposed downstream of a catalyst disposed in an exhaust passage of the internal combustion engine is leaner than a stoichiometric air-fuel ratio, the equivalence ratio correction coefficient is set to a value greater than 1, and when the detected air-fuel ratio is richer than the stoichiometric air-fuel ratio, the equivalence ratio correction coefficient is set to a value less than 1; and the upper limit calculation unit calculates the upper limit to be a larger value as the rotation speed of the internal combustion engine is lower and as the load of the internal combustion engine is lower. This can be achieved by a fuel injection amount control device. Effect of the Invention

[0007] According to the present invention, it is possible to provide a fuel injection amount control device that can appropriately increase the fuel injection amount while suppressing rich misfire. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of the engine. [Diagram 2] FIG. 2 is a flowchart showing an example of the target fuel injection amount calculation control. [Diagram 3] 3A and 3B are maps showing the upper limit value R defined by the engine operating state and the coolant temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Engine outline] FIG. 1 is a schematic diagram of an engine 1. The engine 1 is mounted, for example, in an engine vehicle, but is not limited thereto, and may be mounted in a hybrid vehicle. The engine 1 is, for example, a gasoline engine, which is an example of an internal combustion engine, but is not limited thereto, and may be a diesel engine. Each cylinder 12 of the engine 1 is provided with a piston 13. The piston 13 is connected to a crankshaft 15, which is an output shaft of the engine 1, via a connecting rod 14. The reciprocating motion of the piston 13 is converted into the rotational motion of the crankshaft 15 by the connecting rod 14.

[0010] A combustion chamber 16 is formed above the piston 13 in each cylinder 12, and a spark plug 18 that ignites the mixture of fuel and air is attached to this combustion chamber 16. The timing of ignition of the mixture by this spark plug 18 is adjusted by an igniter 19 provided above the spark plug 18.

[0011] An intake passage 20 and an exhaust passage 21 are connected to the combustion chamber 16. A throttle valve 23 is provided in the intake passage 20 to adjust the amount of air introduced into the combustion chamber 16. A catalyst 50 is provided in the exhaust passage 21, which exerts maximum purification capacity when the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio. The catalyst 50 is a three-way catalyst having an oxygen storage capacity that stores oxygen in exhaust gas that is leaner than the stoichiometric air-fuel ratio and releases the stored oxygen into exhaust gas that is richer than the stoichiometric air-fuel ratio.

[0012] Each intake port 20a constituting a part of the intake passage 20 is provided with a port injection valve 22 for injecting fuel into the intake port 20a for each cylinder 12. The engine 1 is provided with an in-cylinder injection valve 17 for injecting fuel into each combustion chamber 16.

[0013] The ECU (Electronic Control Unit) 30 is an electronic control unit that performs control processing related to the engine 1. The ECU 30 is mainly composed of a computer including a CPU (Central Processing Unit), and volatile and non-volatile memories such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The ECU 30 executes various control processes related to the engine 1 by executing programs installed in the memory on the CPU. Various sensors are connected to the ECU 30, which will be described in detail later. The ECU 30 is an example of a fuel injection amount control device, and functionally realizes a target fuel injection amount calculation unit, a total increase amount calculation unit, and an upper limit value calculation unit, which will be described in detail later.

[0014] An accelerator opening sensor 31, a water temperature sensor 32, an air flow meter 33, a crank angle sensor 34, an upstream air-fuel ratio sensor 35, and a downstream air-fuel ratio sensor 36 are connected to the ECU 30, and output signals from these various sensors are input. The accelerator opening sensor 31 detects the accelerator opening. The water temperature sensor 32 detects the temperature of the cooling water that cools the engine 1. The air flow meter 33 detects the intake air amount. The crank angle sensor 34 detects the rotation angle of the crankshaft 15. The upstream air-fuel ratio sensor 35 is provided in the exhaust passage 21 upstream of the catalyst 50, and detects the air-fuel ratio of the exhaust gas flowing into the catalyst 50. The downstream air-fuel ratio sensor 36 is provided in the exhaust passage 21 downstream of the catalyst 50, and detects the air-fuel ratio of the exhaust gas that has passed through the catalyst 50.

[0015] The ECU 30 calculates the engine speed based on the detection value of the crank angle sensor 34, and calculates the engine load based on the engine speed and the intake air amount. The ECU 30 calculates a target speed and a target load based on the accelerator opening, and controls the fuel injection amount, the intake air amount, and the ignition timing so that the engine speed and the load become the target speed and the target load, respectively. The ECU 30 also controls the injection ratio between the port injection valve 22 and the in-cylinder injection valve 17 by variably setting a port injection ratio P, which indicates the ratio of the injection amount injected from the port injection valve 22 out of the target fuel injection amount described later, within the range of "0≦P≦1".

[0016] The ECU 30 calculates a basic fuel injection amount Qb based on the operating state of the engine 1, i.e., the engine speed and load. Next, the ECU 30 calculates a target fuel injection amount Qt by multiplying the basic fuel injection amount Qb by an increase correction coefficient K, as shown in the following formula (1). The ECU 30 controls the opening and closing operations of the in-cylinder injection valve 17 and the port injection valve 22 according to the port injection ratio P so that the actual fuel injection amount becomes the target fuel injection amount Qt. Qt = Qb × K…(1)

[0017] Further, the ECU 30 calculates an increase correction coefficient K according to the following equation (2). K = Ke + Ku-1…(2)

[0018] The equivalence ratio correction coefficient Ke is a correction coefficient for increasing the basic fuel injection amount Qb so that the equivalence ratio of the actual mixture becomes the target equivalence ratio. The equivalence ratio is an index value that indicates the fuel concentration in the mixture, and is a value obtained by dividing the fuel amount that results in the theoretical air-fuel ratio by the actual fuel amount. The equivalence ratio is "1" when the air-fuel ratio of the mixture is the theoretical air-fuel ratio, a value greater than "1" when the air-fuel ratio is richer than the theoretical air-fuel ratio, and a value less than "1" when the air-fuel ratio is leaner than the theoretical air-fuel ratio.

[0019] The equivalence ratio correction coefficient Ke is set as follows. In order to suppress deterioration of exhaust emissions, when the detected air-fuel ratio of the downstream air-fuel ratio sensor 36 is leaner than the stoichiometric air-fuel ratio, the target equivalence ratio is set to a value greater than "1", and the equivalence ratio correction coefficient Ke is set to a value greater than "1". When the detected air-fuel ratio of the downstream air-fuel ratio sensor 36 is richer than the stoichiometric air-fuel ratio, the target equivalence ratio is set to a value less than "1", and the equivalence ratio correction coefficient Ke is set to a value less than "1". In addition, in order to release oxygen from the catalyst 50 that has an excessive amount of oxygen stored immediately after the fuel cut is resumed, the equivalence ratio correction coefficient Ke is gradually changed from a value greater than "1" to "1" from after the fuel cut is resumed until the detected air-fuel ratio of the downstream air-fuel ratio sensor 36 reverses from lean to rich. During cold start, in order to stabilize combustion, the equivalence ratio correction coefficient Ke is gradually changed from a value greater than "1" toward "1" according to the coolant temperature and the cumulative intake air amount. The equivalence ratio correction coefficient Ke satisfies, for example, 0.9≦Ke≦1.5. For example, when Ke=1.1, 10% of the basic fuel injection amount Qb corresponds to the equivalence ratio increase amount.

[0020] The non-contributing fuel correction coefficient Ku is a correction coefficient for increasing the basic fuel injection amount Qb so as to compensate for the fuel that does not contribute to combustion and adheres to the bore wall surface in the cylinder and the wall surface of the intake port 20a. The non-contributing fuel correction coefficient Ku is an adapted value experimentally obtained in advance based on various data. The non-contributing fuel correction coefficient Ku is set based on a map defined according to the cooling water temperature and the engine load while the engine is running. During intermittent operation in which the engine 1 is automatically stopped and restarted, the non-contributing fuel correction coefficient Ku is calculated based on the above-mentioned cooling water temperature and engine load as well as a map defined according to the engine stop period. In the above map, for example, the lower the cooling water temperature, the smaller the engine load, and the longer the engine stop period, the larger the non-contributing fuel correction coefficient Ku is calculated to be. The non-contributing fuel correction coefficient Ku takes a value that satisfies, for example, 1.0≦Ku≦1.5. For example, when Ku=1.2, 20% of the basic fuel injection amount Qb corresponds to the non-contributing fuel increase.

[0021] The equivalence ratio correction coefficient Ke and the non-contributing fuel correction coefficient Ku thus set are added together, and a value obtained by subtracting "1" from the sum is calculated as the increase correction coefficient K. Therefore, K corresponds to the total increase amount obtained by adding up the equivalence ratio increase amount and the non-contributing fuel increase amount. For example, when Ke=1.1 and Ku=1.2, K=1.3, and the fuel injection amount that is 30% larger than the basic fuel injection amount Qb is calculated as the target fuel injection amount Qt.

[0022] [Target fuel injection amount calculation control] Next, the target fuel injection amount calculation control executed by the ECU 30 will be described. Fig. 2 is a flowchart showing an example of the target fuel injection amount calculation control. This control is repeatedly executed in the ignition-on state. The ECU 30 calculates the increase correction coefficient K based on the above-mentioned formula (2) (step S1). The process of step S1 is an example of the process executed by the total increase amount calculation unit.

[0023] Next, the ECU 30 calculates an upper limit value R (step S2). The upper limit value R is a value that limits the boost correction coefficient K so that a rich misfire does not occur, and is an appropriate value that is experimentally determined in advance based on various data. If a rich misfire occurs, drivability decreases, HC emissions increase, and if the ECU 30 has a self-diagnosis function (OBD: On-Board Diagnostics), there is a risk of it being erroneously diagnosed as abnormal. The ECU 30 calculates the upper limit value R by referring to the following map.

[0024] Figures 3A and 3B are maps showing the upper limit value R defined by the operating state of the engine 1 and the temperature of the cooling water. This map is stored in the memory of the ECU 30. The horizontal axis indicates the engine speed [rpm], and the vertical axis indicates the engine load [N·m]. Figure 3A shows the case where the cooling water is at a high temperature, and Figure 3B shows the case where the cooling water is at a low temperature. In Figure 3A, upper limit values R1 to R7 are shown as an example of the upper limit value R. In Figure 3B, upper limit values R2 to R8 are shown as an example of the upper limit value R. The upper limit values R1 to R8 satisfy the relationship R1 < R2 < R3 < R4 < R5 < R6 < R7 < R8. As shown in Figures 3A and 3B, in any case, the lower the engine speed and the lower the engine load, the upper limit value R is defined to be a larger value. This is because the lower the engine speed, the slower the intake air flow rate, the greater the amount of uncontributed fuel increase in the fuel injection amount that actually adheres to the cylinder inner wall surface, etc., and the greater the amount of surplus fuel until rich misfire occurs. Also, the lower the engine load, the smaller the basic fuel injection amount Qb, so the amount of surplus fuel until rich misfire occurs increases.

[0025] As shown in Figures 3A and 3B, when the operating state of the engine 1 is the same, the lower the temperature of the cooling water, the upper limit value R is defined to be a larger value. This is because the lower the temperature of the cooling water, the greater the amount of uncontributed fuel increase in the fuel injection amount that actually adheres to the cylinder inner wall surface, etc., and the greater the amount of surplus fuel until rich misfire occurs. The process of step S2 is an example of the process executed by the upper limit value calculation unit.

[0026] Next, the ECU 30 judges whether the boost correction coefficient K is equal to or greater than the upper limit value R (step S3). If the answer is No in step S3, the ECU 30 calculates the target fuel injection amount Qt based on the above-mentioned formula (1) (step S4). If the answer is Yes in step S3, the ECU 30 calculates the target fuel injection amount Qt by using the upper limit value R instead of the boost correction coefficient K (step S5). In this way, when the boost correction coefficient K is equal to or greater than the upper limit value R, the boost correction coefficient K is limited to the upper limit value R and the target fuel injection amount Qt is calculated. In this way, the fuel injection amount can be appropriately increased in consideration of the equivalence ratio and the non-contributing fuel amount while suppressing rich misfire. The processes of steps S4 and S5 are an example of the processes executed by the target fuel injection amount calculation unit.

[0027] In the above embodiment, the engine 1 is provided with both the in-cylinder injection valve 17 and the port injection valve 22, but the present invention is not limited to this, and the engine may be provided with either one of the valves. In the above embodiment, the ECU 30 applied to the engine 1 mounted on a vehicle is described as an example of a fuel injection amount control device, but the present invention is not limited to this. For example, the contents of the above embodiment can be applied to a fuel injection amount control device for an engine mounted on a motorcycle or the like, or a fuel injection amount control device for an engine mounted on something other than a vehicle, such as a ship or construction machine.

[0028] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0029] 1 Engine 17 In-cylinder injection valve 22 port injection valve 30 ECU (fuel injection amount control device, target fuel injection amount calculation unit, total increase amount calculation unit, upper limit value calculation unit) 32 Water temperature sensor 36 Downstream air-fuel ratio sensor

Claims

[Claim 1] a target fuel injection amount calculation unit that calculates a target fuel injection amount by correcting the basic fuel injection amount calculated in accordance with an operating state of the internal combustion engine so as to increase the basic fuel injection amount; a total increase amount calculation unit that calculates a total increase amount, which is the sum of an equivalence ratio increase amount, which is an increase correction amount for controlling the equivalence ratio of the mixture to a target equivalence ratio, and a non-contributing fuel increase amount, which is an increase correction amount for compensating for a fuel amount that does not contribute to combustion; an upper limit value calculation unit that calculates an upper limit value of an increase correction based on an operating state of the internal combustion engine and a temperature of a coolant of the internal combustion engine, the target fuel injection amount calculation unit calculates the target fuel injection amount by adding the total increase to the basic fuel injection amount when the total increase is less than the upper limit value, and calculates the target fuel injection amount by adding the upper limit value instead of the total increase to the basic fuel injection amount when the total increase is equal to or greater than the upper limit value; the total increase calculation unit calculates a value obtained by multiplying the basic fuel injection amount by an increase correction coefficient as the total increase amount, the increase correction coefficient is calculated by adding an equivalence ratio correction coefficient, which is a correction coefficient for increasing the basic fuel injection amount so as to compensate for a fuel amount that does not contribute to combustion, to the equivalence ratio correction coefficient, which is a correction coefficient for increasing the basic fuel injection amount so that the equivalence ratio of the actual air-fuel mixture becomes the target equivalence ratio, and further subtracting 1 from the sum, when a detected air-fuel ratio of a downstream air-fuel ratio sensor disposed downstream of a catalyst disposed in an exhaust passage of the internal combustion engine is leaner than a stoichiometric air-fuel ratio, the equivalence ratio correction coefficient is set to a value greater than 1, and when the detected air-fuel ratio is richer than the stoichiometric air-fuel ratio, the equivalence ratio correction coefficient is set to a value less than 1; A fuel injection amount control device, wherein the upper limit calculation unit calculates the upper limit value to be a larger value as the rotation speed of the internal combustion engine and the load on the internal combustion engine are lower.

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