Control device for internal combustion engine

Abstract

To appropriately cope with oxygen deficiency causing start delay or start failure when starting a stopped internal combustion engine, to improve startability.SOLUTION: A controller of an internal combustion engine is configured to: when stopping an internal combustion engine that is being operated by firing, stop fuel injection and combustion to monitor the internal combustion engine by an electric motor; estimate an amount of air having flowed from a suction passage through a cylinder to an exhaust passage during motoring based on at least an engine speed and a motoring time; and determine whether the amount of air exceeds a threshold corresponding to the volume of the cylinder and exhaust passage.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for controlling an internal combustion engine mounted on a vehicle or the like as a power source. [Background technology]

[0002] As is well known, when starting a stopped internal combustion engine, motoring (or cranking) is performed by rotating the crankshaft, which is the output shaft of the internal combustion engine, using an electric motor, while fuel is injected from an injector and burned in the cylinders to accelerate the rotation of the crankshaft. This motoring for starting ends when the internal combustion engine progresses from initial combustion to continuous combustion and the rotation speed of the crankshaft, i.e., the engine speed, exceeds a judgment value determined based on the temperature of the cooling water of the internal combustion engine, and the engine is deemed to have completed combustion (see, for example, the following patent document). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-133592 Summary of the Invention [Problem to be solved by the invention]

[0004] When an internal combustion engine is stopped, the crankshaft may stop rotating due to a valve overlap condition in which both the intake valve and the exhaust valve of one of the cylinders are open. This valve overlap condition is relatively common in in-line three-cylinder internal combustion engines.

[0005] When an internal combustion engine is stopped and both the intake and exhaust valves of a cylinder are open, exhaust gas (i.e., combustion gas) remaining in the exhaust passage when the engine was stopped may flow back through the cylinder from the exhaust passage to the intake passage. This gas has a lower oxygen concentration than normal air (outside air). This causes a decrease in the oxygen concentration in the intake passage connected to the cylinder. In other words, the oxygen concentration in the intake passage is not constant when the internal combustion engine is started.

[0006] If an attempt is made to restart the internal combustion engine after that, an insufficient amount of oxygen will be supplied to the combustion chamber of the cylinder, causing unstable fuel combustion or misfire, which may ultimately lead to delayed or poor starting.

[0007] An intended object of the present invention is to appropriately address oxygen shortage, which is a cause of delayed or poor starting when starting an internal combustion engine that has been stopped, and to improve startability. [Means for solving the problem]

[0008] In the present invention, when stopping an internal combustion engine that is firing and operating, fuel injection and combustion are stopped and the internal combustion engine is motored by an electric motor, and During the motoring, the throttle valve opening is opened larger than the opener opening, The intake valve opening / closing timing of the cylinder is returned to the most retarded timing to minimize the length of the valve overlap period during which both the intake valve and the exhaust valve are open, and the amount of air flowing from the intake passage through the cylinder to the exhaust passage during motoring is estimated based on at least the engine speed, motoring time, and the intake temperature and intake pressure in the intake passage connected to the cylinder, and the amount of air is calculated based on It is the volume of the area where exhaust gas with a lower oxygen concentration than normal air can remain when an internal combustion engine that has been firing is stopped. Determine whether the volume exceeds a threshold value corresponding to the volume of the cylinder and the volume of the exhaust passage. and, on the condition that the amount of air exceeds the threshold value, the motoring is ended and the rotation of the internal combustion engine is stopped. A control device for an internal combustion engine was constructed.

[0011] In the control method for an internal combustion engine according to the present invention, when stopping an internal combustion engine that is firing and operating, fuel injection and combustion are stopped and the internal combustion engine is motored by an electric motor, During the motoring, the throttle valve opening is opened larger than the opener opening,a step of restoring the opening and closing timing of the intake valve of the cylinder to the most retarded timing to minimize the length of the valve overlap period during which both the intake valve and the exhaust valve are open; a step of estimating the amount of air that flows from the intake passage through the cylinder to the exhaust passage during motoring based on at least the engine speed, motoring time, and the intake temperature and intake pressure in the intake passage connected to the cylinder; It is the volume of the area where exhaust gas with a lower oxygen concentration than normal air can remain when an internal combustion engine that has been firing is stopped. determining whether the volume of the cylinder and the volume of the exhaust passage exceed a threshold value; and, on condition that the amount of air exceeds the threshold value, ending the motoring and stopping the rotation of the internal combustion engine. The following will be implemented. [Effects of the Invention]

[0012] According to the present invention, it is possible to appropriately deal with oxygen shortage, which is a cause of delayed or poor starting when starting an internal combustion engine that has been stopped, and to improve startability. [Brief explanation of the drawings]

[0013] [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; DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle according to this embodiment. This internal combustion engine is a spark-ignition, four-stroke reciprocating engine that uses gasoline or the like as fuel and has a plurality of cylinders 1 (for example, an in-line three-cylinder engine; FIG. 1 shows one of these). 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. In addition, 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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).

[0019] An internal combustion engine may be equipped with a VVT (Variable Valve Timing) mechanism 5 that can variably control the opening and closing timing of the intake valve and / or exhaust valve of each cylinder 1. The VVT ​​mechanism 5 may be, for example, a vane-type mechanism that uses hydraulic pressure (lubricating oil pressure) to change the rotational phase of the intake camshaft and / or exhaust camshaft, which drive the opening and closing of the intake and exhaust valves of each cylinder 1, relative to the crankshaft, or an electric-type mechanism (motor-driven VVT) that changes the rotational phase using an electric motor. The camshaft receives rotational torque from the crankshaft and rotates in response to the crankshaft. A power transmission (not shown) for transmitting the rotational torque is interposed between the crankshaft and the camshaft. The power transmission includes a crank sprocket (or pulley) provided on the crankshaft, a cam sprocket (or pulley) provided on the camshaft, and a timing chain (or timing belt) wound around these sprockets (or pulleys). The VVT ​​mechanism 5 changes the rotational phase of the camshaft relative to the crankshaft by rotating the camshaft relative to the cam sprocket, thereby changing the opening and closing timing of the intake valve and / or the exhaust valve.

[0020] The ECU (Electronic Control Unit) 0, 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 ECU 0 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).

[0021] The input interface of the ECU 0 receives a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, 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 depression amount of the accelerator pedal or the opening degree of the throttle valve 32 as the accelerator opening (in other words, the engine torque or engine load factor required for the internal combustion engine), an intake passage 3 connected to the cylinder 1 (downstream of the throttle valve 32, particularly the surge tank 33), The signals input to the catalytic converter 41 include 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 manifold 34 or intake manifold 35; 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 a cam angle signal h output from a cam angle sensor at multiple cam angles of the intake camshaft or exhaust camshaft of the internal combustion engine.

[0022] The output interface of ECU0 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, a valve timing control signal m to the VVT ​​mechanism 5, and the like.

[0023] 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, ignition timing (including the number of spark ignitions per expansion stroke of one cylinder 1), required EGR rate (or EGR gas amount), valve timing, etc. ECU0 applies various control signals i, j, k, l, and m corresponding to the operating parameters via an output interface.

[0024] Furthermore, when starting a stopped internal combustion engine (which may be a cold start or a restart from idle stop), the ECU 0 inputs a control signal o to an electric motor (such as a starter (self-starting motor) or motor generator) associated with the internal combustion engine, and while motoring (cranking) is performed by the electric motor rotating the crankshaft of the internal combustion engine, fuel is injected from the injector 11 and ignited by a spark from the spark plug 12, causing the fuel to burn. Motoring for starting ends when the internal combustion engine progresses from initial combustion to multiple combustions, and the engine speed accelerates and increases until it exceeds the 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 at start-up, the higher the complete combustion determination value is raised.

[0025] Conversely, when the internal combustion engine is firing, i.e., supplying fuel to cylinder 1 and burning it, and the driver of the vehicle turns the ignition switch (or ignition key, power switch) from ON to OFF, the operation of the internal combustion engine will be stopped.

[0026] 2, when stopping the internal combustion engine that has been operating (step S1), the ECU0 of this embodiment stops fuel injection from the injector 11 and ignition combustion by the spark plug 12 (step S2). Then, motoring is performed to rotate the crankshaft of the internal combustion engine using the electric motor (step S3).

[0027] The motoring in step S3 is a procedure for maintaining engine rotation without fuel injection or combustion, thereby sending air that does not contain fuel components from the intake passage 3 through the cylinder 1 to the exhaust passage 4, scavenging and discharging the exhaust gas remaining in the cylinder 1 and the exhaust passage 4.

[0028] During motoring in step S3, it is preferable to open the throttle valve 32 in the intake passage 3 to a degree greater than the so-called opener opening to promote air flow. The opener opening refers to the opening of the throttle valve 32 when no power is supplied to the throttle motor that drives the butterfly valve element of the electronic throttle valve 32 and no force is applied to the valve element from the throttle motor, and can be fully closed, which almost completely blocks the flow of intake air through the intake passage 3, or it can be slightly open to allow a small amount of intake air flow.

[0029] During motoring in step S3, the intake valve and / or exhaust valve opening / closing timing realized by the VVT ​​mechanism 5 is returned to its initial position, i.e., the valve timing when the internal combustion engine is stopped or started, or when the engine is idling or operating at a low load close to idling. For example, the intake valve opening / closing timing of cylinder 1 is returned to its most retarded timing, thereby minimizing the length of the valve overlap period during which both the intake valve and the exhaust valve are open.

[0030] Thus, the ECU 0 estimates the amount of air that has flowed from the intake passage 3 through the cylinder 1 to the exhaust passage 4 during motoring in step S3 (step S4), and compares the amount of air with a threshold value (step S5).

[0031] In step S4, the ECU0 calculates the amount of air that has flowed from the intake passage 3 into the exhaust passage 4 during motoring based on the current engine speed and the length of the motoring execution time in step S3, for example, according to the following formula: Intake air volume [cc] = engine speed [rpm] ÷ 60 [sec / min] ÷ 2 x engine displacement specification value [cc] x intake correction coefficient x motoring execution time [sec] In the above formula, the "displacement specification value" means the actual amount of air that can be drawn in from the intake passage 3 and discharged into the exhaust passage 4 in one cycle (one cycle is the series of intake stroke - compression stroke - expansion stroke - exhaust stroke of cylinder 1) with the opening and closing timing of the intake valve and / or exhaust valve returned to the initial position. This displacement specification value is the total value for all cylinders contained in the internal combustion engine (for a three-cylinder engine, the total value for all three cylinders), and is a constant determined experimentally or set by adapting the design stage. The displacement specification value may be less than the geometric internal volume of cylinder 1, that is, the difference between the volume inside the combustion chamber when the piston is at bottom dead center in cylinder 1 and the volume inside the combustion chamber when it is at top dead center. In addition, the "intake correction coefficient" is a constant that is experimentally determined or set by adaptation in the design stage after assuming in advance the intake temperature and intake pressure (possible range) in the intake passage 3 during motoring in step S3.

[0032] However, the intake temperature and intake pressure in the intake passage 3 during motoring in step S3 may be actually measured with reference to the output signal d of the sensor, and the amount of air flowing from the intake passage 3 through the cylinder 1 to the exhaust passage 4 during motoring may be estimated using the measured values. In this case, in step S4, the amount of inflow air is calculated according to the following formula: Intake air volume [cc] = engine speed [rpm] ÷ 60 [sec / min] ÷ 2 × displacement specification value [cc] × (standard temperature [K] × measured intake pressure [kPa]) ÷ (standard atmospheric pressure [kPa] × (standard temperature [K] + measured intake temperature [℃])) × motoring execution time [sec] The "standard temperature" and the "standard atmospheric pressure" are both constants. For example, the "standard temperature" is 273.15, and the "standard atmospheric pressure" is 101.3.

[0033] The threshold value to be compared with the air amount calculated in step S4 in step S5 is the volume of the area where exhaust gas having a lower oxygen concentration than normal air can remain when the internal combustion engine that has been firing is stopped. That is, Threshold [cc] = Cylinder volume [cc] + Exhaust passage volume [cc] is.

[0034] The "internal volume of a cylinder" is the total value of all cylinders contained in an internal combustion engine, and is a constant determined experimentally or set by design stage adaptation. The "internal volume of the exhaust passage" is a value equivalent to the entire internal volume of the exhaust passage 4 from the exhaust port to the end communicating with the outside, including the exhaust manifold 42, catalyst 41, and further downstream muffler, and is a constant determined experimentally or set by design stage adaptation.

[0035] If the condition of inflow air amount > threshold is met in step S5, this means that the exhaust gas remaining in the exhaust passage 4 has been scavenged and replaced with air by the motoring in step S3. When the condition of step S5 is met, the ECU0 ends motoring of the internal combustion engine (step S6) and stops the rotation of the internal combustion engine.

[0036] According to this embodiment, when the operation of the internal combustion engine is stopped, it is possible to accurately estimate the amount of exhaust gas with a low oxygen concentration remaining in the exhaust passage 4. Furthermore, it is possible to reliably scavenge and discharge the low-oxygen exhaust gas remaining in the exhaust passage 4. Therefore, it is possible to effectively avoid the problem of exhaust gas flowing back from the exhaust passage 4 to the intake passage 3 while the internal combustion engine is stopped, resulting in a decrease in the oxygen concentration in the intake passage 3. This stabilizes fuel combustion when the internal combustion engine is started again, and prevents start delays or start failures.

[0037] There is no need to install a new air-fuel ratio sensor (O2 sensor or linear A / F sensor) at the end of the exhaust passage 4, which prevents a rise in costs.

[0038] The present invention is not limited to the above-described embodiment, and the specific configuration of each unit and the processing procedure can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0039] 0...Control unit (ECU) 1...cylinder 11...Injector 12...Spark plug 2...Exhaust gas recirculation (EGR) device 21...EGR passage 22...EGR cooler 23...EGR valve 3...Intake passage 31...Air cleaner 32...Throttle valve 33...Surge tank 34...Intake manifold 4...Exhaust passage 41...Catalyst 42...Exhaust manifold 43, 44...Air-fuel ratio sensor 5...Variable valve timing (VVT) mechanism a…Vehicle speed signal b...Crank angle signal c...Accelerator opening signal d...Intake temperature / intake pressure signal e...Coolant temperature signal f, g…Air-fuel ratio signal h...Cam angle signal i…Ignition signal j…Fuel injection signal k...Throttle valve opening operation signal l...EGR valve opening operation signal m...Valve timing control signal o...Motor control signal

Claims

1. When stopping an internal combustion engine that is firing and operating, Fuel injection and combustion are stopped and the internal combustion engine is motored by the electric motor, and during this motoring, the throttle valve opening is opened to a larger extent than the opener opening, and the opening and closing timing of the intake valve of the cylinder is returned to the most retarded timing, thereby minimizing the length of the valve overlap period during which both the intake valve and the exhaust valve are open; an amount of air flowing from the intake passage through the cylinder to the exhaust passage during motoring is estimated based on at least the engine speed, the motoring time, the intake temperature and the intake pressure in the intake passage connected to the cylinder; determining whether the amount of air exceeds a threshold value corresponding to a volume of the cylinder and the exhaust passage, which is a volume of an area in which exhaust gas having a lower oxygen concentration than normal air can remain when the internal combustion engine that has been firing is stopped; A control device for an internal combustion engine that ends the motoring and stops the rotation of the internal combustion engine on the condition that the amount of air exceeds the threshold value.

2. When stopping an internal combustion engine that is firing and operating, a step of stopping fuel injection and combustion and motoring the internal combustion engine with an electric motor, and during the motoring, opening the throttle valve to a degree greater than the opener opening, and restoring the opening and closing timing of the intake valve of the cylinder to the most retarded timing, thereby minimizing the length of the valve overlap period during which both the intake valve and the exhaust valve are open; a step of estimating the amount of air flowing from the intake passage through the cylinder to the exhaust passage during motoring based on at least the engine speed, the motoring time, and the intake temperature and intake pressure in the intake passage connected to the cylinder; a step of determining whether the amount of air exceeds a threshold value corresponding to a volume of the cylinder and the exhaust passage, which is a volume of an area in which exhaust gas having a lower oxygen concentration than normal air can remain when the internal combustion engine that has been firing is stopped; ending the motoring and stopping the rotation of the internal combustion engine on condition that the amount of air exceeds the threshold value; A control method for an internal combustion engine that implements the above.

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