Control device for internal combustion engine

Abstract

To surely perform a second injection in multiple injections and improve emission.SOLUTION: A control device for an internal combustion engine controls a port injection type internal combustion engine that injects a fuel from an injector toward an intake port of a cylinder. The control device is configured to, when performing multiple injections in which for one expansion stroke of one cylinder, the fuel is injected from the injector a plurality of times into the cylinder and the fuel of the plurality of times is sucked into the cylinder and combusted, detect variation in a fuel injection quantity for each cylinder and to set a valve opening time for the second fuel injection to a cylinder to be longer, for the cylinder in which the fuel quantity actually injected from the injector is considered to small.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for controlling a port injection type internal combustion engine in which an injector that injects fuel into an intake passage connected to a cylinder is installed. [Background technology]

[0002] In a port-injection internal combustion engine, a control method is known in which a required amount of fuel is injected into a cylinder from an injector in multiple increments for one expansion stroke of that cylinder, and the multiple injections of fuel are drawn into the cylinder and burned (see the following patent document).Multiple injection prevents unatomized (or unvaporized) fuel droplets from entering the combustion chamber of the cylinder, reducing the particulate matter (PM) and particle number (PN) generated during combustion of the air-fuel mixture.

[0003] In multi-injection, for example, the first fuel injection is performed before the intake valve of the cylinder opens (asynchronous injection), and the second fuel injection is performed while the intake valve of the same cylinder is open (synchronous injection). In this case, the amount of fuel injected in the first injection is set large and the amount of fuel injected in the second injection is set small. The time from the second injection to the timing of spark ignition (usually just before the expansion stroke) is shorter than the time from the first injection to the timing of spark ignition. In other words, the second injected fuel has less time to atomize. If the second injection amount is excessive, liquid fuel will be drawn directly into the cylinder, which could actually increase the amount of PM and HC (hydrocarbons) generated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-002790 Summary of the Invention [Problem to be solved by the invention]

[0005] The ECU (Electronic Control Unit), which controls the operation of an internal combustion engine, sends a fuel injection signal to the injector solenoid, opening the injector and injecting fuel.In reality, the injector does not stay open the entire time that the injector solenoid is energized; there is an ineffective injection period when the injector does not open even after energization begins and does not inject fuel, after which the injector opens and enters the effective injection period when it injects fuel.

[0006] Multi-injection is effective in improving emissions immediately after a cold start when the temperatures of the internal combustion engine's cylinders and three-way catalyst for purifying exhaust gas are low. However, the amount of fuel required to be injected into the cylinders during idling immediately after starting is small. Moreover, because the required amount is injected in multiple increments, the amount of fuel injected in the second injection is extremely small, and the time that current is applied to the injector solenoid during the second injection is also very short.

[0007] The individual injectors installed in each cylinder vary in their characteristics, including due to aging. Some injectors are difficult to open and inject fuel. If the power supply time for such an injector is short, most or all of the power supply time will be occupied by ineffective injection time, and the second injection of a multi-injection system will not be performed properly. This can result in insufficient engine torque being generated during the expansion stroke of the cylinder in which the injector is installed, which can lead to undesired fluctuations in engine speed.

[0008] The present invention has been made in view of the above problems, and has as its intended object to reliably carry out the second injection in a multi-injection and to improve emissions. [Means for solving the problem]

[0009] The present invention controls a port injection type internal combustion engine in which fuel is injected from an injector toward the intake port of a cylinder. When performing multi-injection in which fuel is injected from the injector multiple times into a single cylinder for one expansion stroke of the cylinder, and the multiple injections of fuel are drawn into the cylinder and burned, The first fuel injection is performed before the intake valve of a cylinder opens, and the second fuel injection is performed while the intake valve of the same cylinder is open, and the injector opening time for the second fuel injection is shorter than the injector opening time for the first fuel injection, and in the multi-injection Detects variations in fuel injection volume for each cylinder, and for cylinders where the actual amount of fuel injected from the injector is thought to be small, sets the injector valve opening time for the second fuel injection to that cylinder longer. and then corrects the timing of spark ignition of the mixture in the cylinder to be more retarded. A control device for an internal combustion engine was constructed. [Effects of the Invention]

[0011] According to the present invention, the second injection of the multi-injection can be reliably carried out and emissions can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; [Figure 2] 3 is a flowchart showing an example of a procedure of a process executed by the control device for the internal combustion engine according to a program of the embodiment; [Figure 3] 3 is a diagram showing the timing of each fuel injection when multi-injection is performed in the internal combustion engine of the embodiment; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of a vehicle internal combustion engine according to this embodiment. The internal combustion engine according to this embodiment is a spark-ignition, four-stroke gasoline engine having multiple cylinders 1 (e.g., three cylinders, one of which is shown in FIG. 1). An injector 11 that injects fuel toward the intake port is provided near the intake port of each cylinder 1 in the intake passage 3. Incidentally, if each cylinder 1 has two intake ports, an injector 11 is provided for each intake port; in other words, multiple injectors 11 may be provided for one cylinder 1. An ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 receives an induced voltage generated by an ignition coil and generates a spark discharge between a center electrode and a ground electrode.

[0014] An intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. An air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream to downstream in the intake passage 3.

[0015] An exhaust passage 4 for discharging exhaust gases guides exhaust gases generated as a result of fuel combustion in the cylinders 1 to the outside from the exhaust ports of each cylinder 1. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gases are arranged on this exhaust passage 4.

[0016] Air-fuel ratio sensors 43, 44 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4 to detect the air-fuel ratio of the gas flowing through the exhaust passage 4. The air-fuel ratio sensors 43, 44 may each be an O2 sensor having a nonlinear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas.

[0017] The exhaust gas recirculation device 2 includes, as its elements, an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a predetermined position downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a predetermined position downstream of the throttle valve 32 in the intake passage 3 (in particular, a surge tank 33 or an intake manifold 34).

[0018] The ECU0, which is the control device for the internal combustion engine in this embodiment, is a microcomputer system having a processor, a memory, an input interface, an output interface, etc. The ECU0 may be configured by connecting a plurality of ECUs or controllers to each other so that they can communicate with each other via an electric communication line such as a CAN (Controller Area Network).

[0019] The input interface of ECU0 receives inputs such as a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft of the internal combustion engine and the engine speed, an accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as the accelerator opening (in other words, the engine torque or engine load factor required by the internal combustion engine), an intake air temperature / intake pressure signal d output from a temperature / pressure sensor that detects the intake air temperature and intake pressure in the intake passage 3 (particularly the surge tank 33 or the intake manifold 34) connected to the cylinder 1, a coolant temperature signal e output from a water temperature sensor that detects the coolant temperature of the internal combustion engine, a signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41, a signal g output from an air-fuel ratio sensor 44 that detects the air-fuel ratio of the exhaust gas downstream of the catalyst 41, and an atmospheric pressure signal h output from an atmospheric pressure sensor that detects the atmospheric pressure.

[0020] The output interface of the ECU 0 outputs an ignition signal i to the igniter of the spark plug 12, a fuel injection signal j to the solenoid of the injector 11, an opening operation signal k to the throttle valve 32, an opening operation signal l to the EGR valve 23, and the like.

[0021] The processor of ECU0 interprets and executes programs stored in memory in advance, calculates operating parameters, and controls the operation of the internal combustion engine. ECU0 acquires various pieces of information a, b, c, d, e, f, g, and h required for controlling the operation of the internal combustion engine via an input interface, determines the engine speed, and estimates the amount of air (fresh air) to be drawn into cylinder 1. Based on the engine speed and intake air amount, ECU0 determines various operating parameters such as the required fuel injection amount, fuel injection timing (including the number of fuel injections per expansion stroke of one cylinder 1), fuel injection pressure, required EGR rate (or EGR gas amount), and ignition timing (including the number of spark ignitions per expansion stroke of one cylinder 1). ECU0 applies various control signals i, j, k, and l corresponding to the operating parameters via an output interface.

[0022] Furthermore, when starting a stopped internal combustion engine (which may be a cold start or a restart from an idle stop), the ECU 0 inputs a control signal o to an electric motor associated with the internal combustion engine, which rotates and drives the crankshaft of the internal combustion engine while injecting fuel from the injector 11 and igniting it with a spark from the spark plug 12 to burn the fuel, thereby performing cranking. Cranking ends when the internal combustion engine progresses from initial combustion to multiple combustions, and the engine speed accelerates and increases until it exceeds a complete combustion determination value. The complete combustion determination value can fluctuate depending on the temperature of the internal combustion engine, etc. Basically, the lower the coolant temperature of the internal combustion engine, the higher the complete combustion determination value is raised.

[0023] To determine the amount of fuel injection for cylinder 1, ECU0 first calculates the amount of air taken into cylinder 1 and then determines a basic amount of fuel injection TP that is proportional to the amount of intake air (so that the theoretical air-fuel ratio or an air-fuel ratio close to it can be achieved depending on the amount of intake air). The amount of intake air is estimated based on the actually measured engine speed and intake pressure. If necessary, the estimated value can be corrected according to the intake temperature, atmospheric pressure, etc. If an air flow meter is installed in the intake passage 3, the amount of intake air can be directly measured via the air flow meter.

[0024] Next, this basic injection amount TP is corrected by a feedback correction coefficient FAF corresponding to the deviation between the air-fuel ratio of the gas flowing into the catalyst 41 and its target value, and various correction coefficients K determined according to environmental conditions and other circumstances (correction coefficients FAF and K are each positive numbers that increase or decrease around 1). The required fuel injection amount TD is TD=TP×FAF×K This becomes:

[0025] In this embodiment, a "single injection" can be performed in which the entire required injection amount TD to be supplied for one expansion stroke of each cylinder 1 is injected in one shot from the injector 11 facing that cylinder 1. Alternatively, a "multiple injection" can be performed in which the required injection amount TD of fuel is injected multiple times, F1 and F2, from the injector 11 facing that cylinder 1.

[0026] As shown in Figure 3, in multi-injection, the first injection (asynchronous injection) F1 is performed during the exhaust stroke before the intake valve of cylinder 1 opens, and the second injection (synchronous injection) F2 is performed in time with the intake stroke when the intake valve of the cylinder opens. In multi-injection, the proportion of the injection amount of the first injection F1 out of the required injection amount TD is set high (for example, to about 80% to 95% of the required injection amount TD), and the proportion of the injection amount of the second injection F2 is set smaller (for example, to about 5% to 20% of the required injection amount TD). If the proportion of the injection amount of the first injection F1 is R (proportion R is a positive number less than or equal to 1) and the proportion of the injection amount of the second injection F2 is (1-R), the length of time T1 during which current is applied to the solenoid of injector 11 in the first injection F1 is T1=TD×R+TAUV The length of time T2 during which the solenoid of the injector 11 is energized in the second injection F2 is T2=TD×(1-R)+TAUV Here, TAUV is the ineffective injection time during which the injector 11 does not open or does not inject fuel even when the solenoid of the injector 11 is energized. The ECU 0 inputs a signal j to the injector 11 for the energization time T1 at the timing of the first fuel injection F1, thereby opening the injector 11 and injecting fuel. Also, the ECU 0 inputs a signal j to the injector 11 for the energization time T2 at the timing of the second fuel injection F2, thereby opening the injector 11 and injecting fuel.

[0027] In addition, in the case where a plurality of injectors 11 are provided for one cylinder 1, one of them may inject fuel for the first time F1 and the other may inject fuel for the second time F2, or both injectors 11 may inject fuel for the first time F1 and the second time F2, respectively. When both injectors 11 inject fuel for the first time F1 and the second time F2, the lengths of time T1 and T2 for which the solenoid of each injector 11 is energized are T1=(TD / 2)×R+TAUV T2=(TD / 2)×(1-R)+TAUV This becomes:

[0028] It is preferable to perform multiple injection immediately after starting the internal combustion engine. When the temperature of the internal combustion engine is low, single injection makes it difficult to atomize (or vaporize) the fuel sufficiently, and fuel droplets flow into the combustion chamber of cylinder 1, making it more likely that PM will be generated in the combustion chamber. Multiple injection can suppress the flow of fuel droplets into the combustion chamber, reducing the amount of PM and PN. Of course, multiple injection can also be performed after the internal combustion engine has finished warming up.

[0029] However, individual differences in the characteristics of the individual injectors 11 installed in each cylinder 1, including changes over time, inevitably occur. Some injectors 11 may be difficult to open or difficult to inject fuel. In such injectors 11, most or all of the energization time T2 of the second F2 injection in multi-injection is occupied by the invalid injection time TAUV, and the second F2 injection may not be performed properly.

[0030] This problem becomes particularly apparent during idling immediately after starting, when the required injection amount TD is inherently small and the current application time T2 for the second injection F2 is significantly short. For example, if the current application time T2 is 1050 microseconds, of which the invalid injection time TAUV is 1000 microseconds, and it is sufficient for the injector 11 to inject fuel for only 50 microseconds as the effective injection time, this may not be realized depending on the characteristics of the injector 11, and the fuel injection amount for the second injection F2 may be almost zero.

[0031] Therefore, as shown in FIG. 2, when the time elapsed since the cold start of the internal combustion engine is less than a predetermined value, or the current cooling water temperature of the internal combustion engine is less than a predetermined value (step S1), and multi-injection is to be performed (step S2), the ECU0 of this embodiment detects the variation in the fuel injection amount for each cylinder 1 or for each individual injector 11 installed in each cylinder 1 (step S3), and for a cylinder 1 for which the amount of fuel actually injected from the injector 11 is thought to be small, sets the valve opening time T2 of the injector 11 for the second fuel injection F2 for that cylinder 1 to be longer (step S4).

[0032] In step S3, ECU0 identifies the cylinder 1 for which the amount of fuel injected from the injector 11 in the second F2 is insufficient, in other words, the cylinder 1 for which the engine torque is not sufficiently output during the expansion stroke, based on, for example, a time series of instantaneous values of the rotational speed of the crankshaft obtained by referring to the output signal b of the crank angle sensor.

[0033] ECU0 repeatedly measures the time required for the crankshaft to rotate a predetermined crank angle, typically 30° CA, by referencing the pulse train of crank angle signal b. At the same time, ECU0 obtains the change in the required time for 30° CA by subtracting the previously measured time from the currently measured time. A positive change in the required time for 30° CA indicates a decrease (deceleration) in the crankshaft rotation speed, while a negative change indicates an increase (acceleration) in the crankshaft rotation speed. The crankshaft rotation speed per 30° CA or the required time for each 30° CA is not constant; it is fastest during the expansion stroke of each cylinder 1 and slowest midway between the expansion strokes of one cylinder 1 and the next. Therefore, the time series of the required time for each 30° CA pulsates with the period when each cylinder 1 enters the expansion stroke. However, if the amount of fuel injected from the injector 11 for the second time F2 is insufficient and sufficient torque is not output during the expansion stroke of cylinder 1, the rotation of the crankshaft will not accelerate properly, and the rotational speed of the crankshaft per 30° CA will drop unduly, i.e., the time required for each 30° CA will become unduly long.

[0034] In step S3, when the change in the required time for 30° CA (= required time this time - required time last time) is a positive value and exceeds the judgment value, the ECU0 judges that an event of a drop in the rotation speed of the crankshaft has occurred, that is, that sufficient torque was not output in the cylinder 1 that has recently undergone the expansion stroke. This means that the amount of fuel injected in the second F2 from the injector 11 that injects fuel into the cylinder 1 is unduly small, or that the second F2 fuel injection has not actually been performed. In step S4, the ECU0 applies a correction to extend the energization time T2 for the second F2 fuel injection from the injector 11 that injects fuel into the cylinder 1. In the subsequent fuel injection control, the energization time T2 for this injector 11 is determined by taking into account the increase correction coefficient A (correction coefficient A is a positive number greater than 1). T2 = (TD) × (1-R) × A + TAUV or T2=(TD / 2)×(1-R)×A+TAUV As already mentioned, the latter equation is the current application time T2 when fuel is injected from both of the two injectors 11 into one cylinder 1 for the first injection F1 and the second injection F2.

[0035] After correcting the energization time T2 for the individual injector 11 that is difficult to inject fuel in this way, a correction is made to further retard the spark ignition timing of the air-fuel mixture in each cylinder 1 (step S5). The retarding of the ignition timing in step S5 is intended to delay the start of combustion of the air-fuel mixture in the combustion chamber of cylinder 1, ensuring the combustion of high-concentration HC trapped between the ceiling of the combustion chamber and the piston top land, thereby reducing their emissions. In addition, retarding the ignition timing also aims to increase the temperature of the gas discharged from cylinder 1 into the exhaust passage 4 and flowing into the catalyst 41, thereby quickly raising the temperature of the catalyst 41 and activating it.

[0036] During the above-described retard correction of the ignition timing, a correction may be made in parallel to this, such that the required fuel injection amount TD is further increased, or the energization time T1 and / or T2 of the injector 11 is further extended.

[0037] In this embodiment, the present invention controls a port injection type internal combustion engine in which fuel is injected from an injector 11 toward the intake port of a cylinder 1. When performing multi-injection (step S2), in which fuel F1 and F2 are injected from the injector 11 multiple times into one cylinder 1 for one expansion stroke of that cylinder 1, and the fuel F1 and F2 is drawn into the cylinder 1 and burned, the control device 0 of the internal combustion engine detects variations in the fuel injection amount for each cylinder 1 (step S3), and for a cylinder 1 in which the amount of fuel actually injected from the injector 11 is thought to be small, the control device 0 sets the valve opening time T2 of the injector 11 for the second F2 fuel injection into that cylinder 1 to be longer.

[0038] According to this embodiment, the second injection F2 in the multi-injection can be reliably performed, and sufficient engine torque can be generated during the expansion stroke of each cylinder 1. Therefore, undesirable fluctuations in engine speed can be avoided. Furthermore, multi-injection makes it possible to suppress the generation of PM and PN, especially before the internal combustion engine is warmed up.

[0039] Furthermore, for cylinder 1 where the amount of fuel actually injected from injector 11 is thought to be small, the valve opening time T2 of injector 11 for the second F2 fuel injection into that cylinder 1 is set longer (step S4), and then the spark ignition timing of the mixture in cylinder 1 is corrected to be more retarded (step S5). Retardation of the ignition timing contributes to reducing HC emissions before the internal combustion engine is warmed up. Step S5 is performed after step S4 is performed in order to start the ignition retard correction in step S5 after ensuring that the required amount of fuel TD can be injected toward cylinder 1 through step S4, thereby avoiding destabilization of ignition and combustion of the mixture.

[0040] Overall, emissions can be improved, particularly immediately after a cold start of the internal combustion engine.

[0041] Note that the present invention is not limited to the embodiment described above. For example, in step S3, to detect variations in the fuel injection amount for each cylinder 1 or for each individual injector 11 installed in each cylinder 1, instead of referring to the crank angle signal b, it is also possible to refer to the amount of ionic current generated in the combustion chamber of the cylinder 1 when the mixture is burned, the output signal of an in-cylinder pressure sensor that measures the pressure in the combustion chamber, or the output signal f of the air-fuel ratio sensor 43. For cylinders 1 where the amount of ionic current generated is small, the in-cylinder pressure during the expansion stroke is low, or the air-fuel ratio of the gas discharged from the cylinder 1 after the expansion stroke is lean, the amount of fuel injected in the second injection F2 may be insufficient.

[0042] In addition, the specific configuration of each part and the processing procedure can be modified in various ways without departing from the spirit of the present invention. [Industrial Applicability]

[0043] The present invention can be applied to an internal combustion engine mounted on a vehicle or the like. [Explanation of symbols]

[0044] 0...Control unit (ECU) 1...cylinder 11...Injector 12...Spark plug 3...Intake passage 4...Exhaust passage 41...Catalyst b...Crank angle signal d...Intake temperature / intake pressure signal e...Coolant temperature signal i…Ignition signal j…Fuel injection signal

Claims

[Claim 1] This controls a port injection type internal combustion engine that injects fuel from an injector toward the intake port of a cylinder, When performing multi-injection, in which fuel is injected from the injector into a cylinder multiple times for one expansion stroke of that cylinder, and the multiple fuel injections are drawn into the cylinder and burned, the first fuel injection is performed before the intake valve of the cylinder opens, and the second fuel injection is performed while the intake valve of the same cylinder is open, and the injector opening time for the second fuel injection is shorter than the injector opening time for the first fuel injection, In the multi-injection, the control device for an internal combustion engine detects variations in the fuel injection amount for each cylinder, and for a cylinder in which the amount of fuel actually injected from the injector is thought to be small, sets the injector valve opening time for the second fuel injection into that cylinder longer and makes a correction to further retard the spark ignition timing of the mixture in that cylinder thereafter.

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