JP2024080312A - Start control device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to provide a start control device for an internal combustion engine that can appropriately start an internal combustion engine from a state in which the internal combustion engine is rotating at a high rotation speed.
[Solution] When the rotation speed of the internal combustion engine is below a predetermined specified rotation speed, fixed start control is executed (step S5) to control the fuel injection amount of the fuel injection device, the ignition timing at the ignition timing, and the closing timing of the intake valve regardless of the amount of air supplied to the internal combustion engine, and when the rotation speed of the internal combustion engine is higher than the predetermined rotation speed, proper start control is executed (step S6) to control at least one of the fuel injection amount, ignition timing, and valve closing timing based on the amount of air.
[Selected figure] Figure 2

Description

The present invention relates to a device for controlling the start-up of an internal combustion engine.

Patent Document 1 describes a control device for a hybrid vehicle that includes a power split mechanism formed by a single-pinion planetary gear mechanism to which an engine, a first motor, and drive wheels are connected, and a second motor that is provided so as to be able to transmit torque between the output element of the power split mechanism and the drive wheels. This control device is configured to suppress the occurrence of tooth strike between the gears that constitute the power split mechanism when the engine is motored by the first motor and the vehicle is traveling under braking. Specifically, the control device is configured to control the engine speed to a speed equal to or higher than a predetermined specified speed, and to compensate for the braking force difference between the braking force generated by the engine and the target braking force by regeneratively controlling the second motor. The control device is configured to start the engine when the running power required for the hybrid vehicle becomes equal to or higher than a predetermined specified power.

Patent Document 2 describes a control device that improves the responsiveness of the increase in driving force when switching from EV driving, which runs only on the power of the second motor, to a driving mode that involves starting the engine, in a hybrid vehicle configured similarly to the hybrid vehicle described in Patent Document 1. This control device is configured to crank the engine using the first motor when there is a request to start the engine during EV driving, which runs only on the power of the second motor, and to advance the intake valve timing of the engine by a predetermined amount during the cranking period, and to further increase the advance amount after the first explosion of the engine.

JP 2013-91346 A JP 2016-132426 A

The control device described in Patent Document 1 uses the first motor to motor so that the engine speed is equal to or higher than a predetermined speed in order to generate a braking force. When the running power required for the hybrid vehicle is equal to or higher than the predetermined power while the engine speed is maintained at a high speed, the amount of intake air increases compared to when the engine is started from a state where the engine speed is zero. On the other hand, when the engine is started from a state where the engine speed is zero, the amount of intake air cannot be accurately calculated using an air flow meter or the like. Therefore, it is usually assumed that a predetermined amount of air is taken in, and fuel equivalent to that amount of air is injected. In other words, the amount of fuel injected at the time of engine start is usually set to a fixed value. Therefore, if a predetermined amount of fuel is injected at a time when the engine speed is high, the operating state will not correspond to the actual amount of intake air, such as lean combustion, and hesitation will occur at the time of engine start, which may deteriorate the startability.

The present invention was made with a focus on the above technical problems, and aims to provide an internal combustion engine start control device that can properly start an internal combustion engine when the internal combustion engine is rotating at a high rotation speed.

To achieve the above object, the present invention provides a start control device for an internal combustion engine having a fuel injection device that injects fuel, an intake valve that opens and closes an intake port of a cylinder to which air and the fuel are supplied, and an ignition device that ignites the mixture of the air and the fuel, and a controller that controls the fuel injection device, the ignition device, and the intake valve, and when the rotation speed of the internal combustion engine is equal to or lower than a predetermined rotation speed, the controller executes fixed start control that controls the fuel injection amount of the fuel injection device, the ignition timing of the ignition device, and the closing timing of the intake valve regardless of the amount of air supplied to the internal combustion engine, and when the rotation speed of the internal combustion engine is higher than the predetermined rotation speed, the controller executes proper start control that controls at least one of the fuel injection amount, the ignition timing, and the closing timing based on the amount of air.

In the present invention, the controller may execute either the fixed start control or the appropriate start control when there is a start request to burn the mixture to generate power and the temperature of the internal combustion engine is below a predetermined temperature.

In the present invention, the proper start control may determine a target value of the equivalence ratio by dividing the theoretical air-fuel ratio by the actual air-fuel ratio, obtain a target fuel injection amount by multiplying the target value by the air amount, and control the fuel injection device based on the target fuel injection amount.

In the present invention, the proper start control may advance the ignition timing the smaller the amount of air.

In the present invention, the proper start control may advance the valve closing timing the smaller the amount of air is.

According to the present invention, when the rotation speed of the internal combustion engine is equal to or lower than a predetermined rotation speed, the fuel injection amount, ignition timing, or valve closing timing is controlled regardless of the amount of air supplied to the internal combustion engine, whereas when the rotation speed of the internal combustion engine is higher than the predetermined rotation speed, the fuel injection amount, ignition timing, or valve closing timing is controlled based on the amount of air supplied to the internal combustion engine. Therefore, when a request to start the internal combustion engine is made while the internal combustion engine is rotating at a high rotation speed, the startability can be improved by setting the air-fuel ratio of the internal combustion engine to an appropriate air-fuel ratio or by setting the ignition timing to an appropriate timing to increase the combustion speed or improve the combustion efficiency.

1 is a schematic diagram for explaining an example of an internal combustion engine according to an embodiment of the present invention. 4 is a flowchart illustrating an example of control executed by a starting control device according to an embodiment of the present invention. FIG. 4 is a block diagram for explaining an example of determining a fuel injection amount by fixed start control. FIG. 2 is a block diagram for explaining an example of determining ignition timing by fixed start control. FIG. 4 is a block diagram for explaining an example of determining the closing timing of the intake valve by fixed start control. FIG. 4 is a block diagram for explaining an example of determining a fuel injection amount by proper start control. FIG. 2 is a block diagram for explaining an example of determining ignition timing by proper start control. FIG. 4 is a block diagram for explaining an example of determining the intake valve closing timing by proper start control.

The present invention will be described based on the embodiment shown in the figures. Note that the embodiment described below is merely one example of a specific embodiment of the present invention and does not limit the present invention.

1 shows an example of an internal combustion engine according to an embodiment of the present invention. The internal combustion engine (hereinafter, referred to as the engine) 1 shown in FIG. 1 can be configured in the same manner as an engine installed in a conventional vehicle. That is, the engine includes a cylinder block 3 in which a cylinder 2 is formed, and a cylinder head 4 attached above the cylinder block 3. The cylinder head 4 is connected to an intake pipe 5 that feeds outside air into the cylinder 2, and an exhaust pipe 6 that discharges exhaust gas generated in the cylinder 2. The cylinder head 4 is also provided with an intake valve 8 that opens and closes an intake port 7 that communicates with the intake pipe 5, and an exhaust valve 10 that opens and closes an exhaust port 9 that communicates with the exhaust pipe 6. Therefore, air is taken in from the intake pipe 5 into the cylinder 2 by opening the intake valve 8, and exhaust gas in the cylinder 2 is discharged to the exhaust pipe 6 by opening the exhaust valve 10. Although only one cylinder 2 is shown in FIG. 1 for convenience, the engine may be a multi-cylinder engine.

An air filter 11 is provided upstream of the intake pipe 5 to remove foreign matter contained in the outside air, and an air flow meter 12 for detecting the amount of intake air and an intake air temperature sensor 13 for detecting the temperature of the intake air are provided downstream of the air filter 11. A throttle valve 14 for controlling the amount of intake air and a throttle position sensor 15 for detecting the opening degree of the throttle valve 14 are provided downstream of the sensors 12 and 13. An intake manifold 16 for distributing and supplying the intake air to a number of cylinders is provided downstream of the throttle valve 14 in the intake pipe 5, and a pressure sensor 17 for detecting the pressure inside the intake manifold 16 is provided. The intake manifold 16 also functions as a surge tank to dampen the pulsation of the air flowing through the intake pipe 5.

A first catalyst 18 and a second catalyst 19 are provided in series in the exhaust pipe 6 to purify carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust. A/F sensors 20 and 21 for detecting the air-fuel ratio are provided upstream of the first catalyst 18 and between the first catalyst 18 and the second catalyst 19.

An EGR passage 22 that recirculates a portion of the exhaust gas back into the intake air is connected to the intake pipe 5 and exhaust pipe 6. Specifically, the EGR passage 22 is connected to the exhaust pipe 6 between the first catalyst 18 and the second catalyst 19, and to the intake pipe 5 downstream of the intake manifold 16. The EGR passage 22 is provided with an EGR cooler 23 that cools the exhaust gas, and an EGR valve 24 that controls the flow rate of the exhaust gas flowing through the EGR passage 22.

The engine 1 shown in FIG. 1 is also provided with a direct injection injector 25 that injects fuel directly into the cylinder 2, and a port injection injector 26 that injects fuel from the intake pipe 5 into the cylinder 2 via the intake port 7. A high-pressure delivery pipe 27 is connected to the direct injection injector 25, and a high-pressure fuel pump 28 is connected to the high-pressure delivery pipe 27. This high-pressure fuel pump 28 is configured to pressurize fuel pumped from a fuel tank (not shown) and send it to the high-pressure delivery pipe 27. These injectors 25, 26 correspond to the "fuel injection device" in the embodiment of the present invention. A fuel pressure sensor 29 is provided to detect the fuel pressure in the high-pressure delivery pipe 27.

The engine 1 is provided with a camshaft (not shown) connected to the crankshaft 30 by a chain (not shown) or the like, and is configured to open and close the intake valve 8 and exhaust valve 10 by the camshaft. In addition, a variable valve timing mechanism (hereinafter referred to as In-VVT) 31 that can change the timing at which the intake valve 8 opens and closes, and a variable valve timing mechanism (hereinafter referred to as Ex-VVT) 32 that can change the timing at which the exhaust valve 10 opens and closes are provided. These VVTs 31, 32 are configured to be controlled by hydraulic pressure, and are provided with an oil pump 33 that generates the hydraulic pressure, and an oil control valve 34 that controls the oil flowing through the VVTs 31, 32.

The engine 1 is provided with a water jacket 35 surrounding the cylinder 2, and a water temperature sensor 36 for detecting the temperature of the cooling water flowing in the water jacket 35. In addition, a knock sensor 37 for detecting knocking, an ignition device 38 for igniting the mixture in the cylinder 2, and an ignition coil 39 for controlling the ignition device 38 are provided. In addition, a radiator 40 for cooling the cooling water, an electric water pump 41 for moving the cooling water, and a thermostat 42 for prohibiting the cooling water from flowing to the radiator 40 are provided. In addition, various sensors are provided, such as an oil temperature sensor 43 for detecting the temperature of the oil discharged from the oil pump 33, an oil pressure sensor 44 for detecting the oil pressure, a crank angle sensor 45 for detecting the rotation angle of the crankshaft 30, and sensors 46 and 47 for detecting the rotation angle of the camshaft.

Signals from the above-mentioned sensors and various sensors provided on the vehicle, such as an accelerator opening sensor that detects the amount of operation of an accelerator pedal (not shown), are input to an electronic control unit (hereinafter referred to as ECU) 48 for controlling the engine 1. This ECU 48 is mainly composed of a microcomputer, and is configured to output signals to devices that control the engine 1, such as the throttle valve 14, each VVT 31, 32, ignition coil 39, each injector 25, 26, based on signals input from each sensor and pre-stored arithmetic expressions and maps. This ECU 48 corresponds to the "controller" in this embodiment of the present invention.

Figure 2 shows an example of the control executed by the ECU 48. In the example shown in Figure 2, first, it is determined whether there is a request to start the engine 1 (step S1). Starting the engine 1 in this step S1 means generating power by the engine 1, that is, starting the combustion of a mixture of fuel and air. Therefore, for example, if fuel cut control is being executed and the engine 1 is being run without outputting power, a negative determination is made in step S1.

As described above, if there is no request to start engine 1 and therefore step S1 returns a negative result, this routine is terminated. On the other hand, if there is a request to start engine 1 and therefore step S1 returns a positive result, then it is determined whether or not this is the first start (step S2). This step S2 is a step for determining whether or not this is the first start of engine 1 since the system was started, and therefore the determination can be made based on the history since the system was started.

When engine 1 is mounted on a hybrid vehicle, engine 1 can be stopped once and the vehicle can run using only the motor as a driving force source. When engine 1 is then started again, the engine may start in a state (e.g., temperature) that is equivalent to an initial start of engine 1. Therefore, in step S2, it may be determined whether the engine has started in a state that is equivalent to an initial start. Specifically, it may be determined whether the water temperature detected by water temperature sensor 36 is equal to or lower than a predetermined temperature.

If the result of step S2 is negative because it is not the first start, the engine 1 is started using the intermittent start control in conventional vehicles (step S3), and this routine ends for the time being. This intermittent start control is similar to the start control executed in conventional vehicles, and starts the engine 1 by controlling the fuel injection amount, ignition timing, or the advance amount of the intake valve 8 based on parameters such as the throttle opening, engine speed, and engine water temperature.

If step S2 is judged to be positive because it is the first start, it is judged whether the engine speed is higher than a predetermined speed (step S4). This predetermined speed can be set to a predetermined starting speed for starting the engine 1 when it is not rotating. In other words, it can be set to a speed at which the engine can be started by injecting a predetermined amount of fuel in response to the case where the engine 1 is rotating at the starting speed.

If the engine speed is below the predetermined speed and the result of step S4 is negative, the amount of intake air to engine 1 cannot be determined accurately, so fixed start control is executed (step S5) and this routine is temporarily terminated.

This fixed start control is similar to the control executed during conventional engine start-up, and is configured to determine in advance, through experiments, the amount of intake air into cylinder 2 when the engine speed becomes the starting speed, and to control the fuel injection amount based on a predetermined fuel amount according to that intake air amount and the target air-fuel ratio.

In fixed start control, as shown in FIG. 3, first, the number of injections determined based on the engine speed and the engine water temperature are acquired. This number of injections is the number of times fuel is directly injected into the cylinder 2 between the intake stroke and the compression stroke in one cycle, and is configured to set the number of injections to be smaller, for example, as the engine speed is higher. In addition, the engine water temperature can be detected by the water temperature sensor 36.

Based on the number of injections and the engine water temperature, the amount of fuel injected from the direct injector 25 and the port injector 26 is calculated. Specifically, a map for calculating the amount of fuel injected from the direct injector 25 and the port injector 26 using the number of injections and the engine water temperature as parameters is stored in the ECU 48 in advance, and the amount of fuel injected from the direct injector 25 and the port injector 26 is calculated based on the map. Note that the above map is configured so that, for example, the more the number of injections or the lower the engine water temperature, the greater the injection amount of the direct injector 25 (hereinafter referred to as the direct injection amount) and the smaller the injection amount of the port injector 26 (hereinafter referred to as the port injection amount), and conversely, the less the number of injections or the higher the engine water temperature, the greater the port injection amount and the smaller the direct injection amount.

These direct injection amounts and port injection amounts are added together, and the resulting provisional total fuel amount is multiplied by a correction coefficient. The correction coefficients are a correction coefficient according to the engine speed and a correction coefficient according to the atmospheric pressure. The correction coefficient according to the engine speed is set to a larger value the higher the engine speed is, and similarly, the correction coefficient according to the atmospheric pressure is set to a larger value the higher the atmospheric pressure is. The provisional total fuel amount is then multiplied by the correction coefficient to obtain the target fuel injection amount. In other words, the fixed start control is configured to determine the fuel injection amount without estimating or detecting the intake air amount. This is because when the engine speed is at a predetermined speed, the intake air amount cannot be accurately detected by the air flow meter 12.

In addition, fixed start control is configured to determine the ignition timing as shown in FIG. 4. That is, the engine water temperature is detected by the water temperature sensor 36, and the higher the engine water temperature is, the earlier (advanced) the ignition timing is. As described above, fixed start control is configured to determine the ignition timing without estimating or detecting the intake air volume.

Furthermore, the fixed start control is configured to control the opening and closing timing (valve timing) of the intake valve 8 as shown in FIG. 5. That is, the In-VVT 31 is controlled. Specifically, the engine water temperature is detected by the water temperature sensor 36, and the lower the engine water temperature is, the earlier the closing timing of the intake valve 8 is advanced. Also, the lower the engine speed is, the earlier the closing timing of the intake valve 8 is advanced. As described above, the fixed start control is configured to determine the closing timing of the intake valve 8 without estimating or detecting the intake air volume.

On the other hand, if the engine speed is higher than the predetermined speed and the result of step S4 is affirmative, proper start control is executed (step S6) and the routine is temporarily terminated. This proper start control is configured to determine the amount of fuel injection according to the amount of intake air.

In proper start control, first, the number of injections and the engine water temperature are taken in as shown in Figure 6. When fuel is injected in multiple instalments, the total amount of fuel injection needs to be greater than when fuel is injected all at once, and when the engine water temperature is low, more fuel needs to be injected. Therefore, based on the number of injections and the engine water temperature, a target value for the equivalence ratio (hereinafter referred to as the target equivalence ratio) is first calculated. Note that the equivalence ratio is the theoretical air-fuel ratio divided by the actual air-fuel ratio, and therefore, when the engine is started, the target equivalence ratio is set to a value greater than "1".

Then, the A/F injection amount is calculated by multiplying the target equivalence ratio by the intake air amount and the A/F learning value. Since this proper start control is executed when the engine speed is equal to or higher than a predetermined speed, the air flow through the intake pipe 5 is stable (without pulsation), and the air amount detected by the air flow meter 12 is stable and highly accurate. Therefore, the air amount detected by the air flow meter 12 is used as the intake air amount. The A/F learning value is a learning value that takes into account the variation of the A/F sensors 20, 21.

The wet injection amount is added to the A/F injection amount calculated as above. This wet injection amount is the fuel that is injected into cylinder 2 and does not evaporate (volatilize) and adheres to the inside of cylinder 2. The fewer the number of injections, the greater the amount of fuel injected at one time, and therefore the greater the wet injection amount. Also, the lower the engine water temperature, the greater the wet injection amount.

Then, the A/F injection amount is added to the wet injection amount, and then multiplied by the intake pressure correction value to obtain the target fuel injection amount. This intake pressure correction value is a value according to the intake pressure detected by the pressure sensor 17, and is set to a larger value as the intake pressure is higher. In other words, it is configured to increase the target fuel injection amount as the intake pressure is higher.

In addition, the proper start control is configured to determine the ignition timing based on the engine water temperature, engine speed, and air load factor, as shown in FIG. 7. Specifically, the lower the engine water temperature, the more advanced the ignition timing is. Also, the higher the engine speed, the more advanced the ignition timing is. Furthermore, the air load factor is the ratio of the actual intake air volume to the amount of intake air that can be inhaled, and can be calculated based on the volume of the engine 1 (cylinder 2) and the amount of air detected by the air flow meter 12, and the smaller the air load factor, the more advanced the ignition timing is. In other words, the smaller the amount of intake air, the more advanced the ignition timing is.

Furthermore, the proper start control is configured to control the opening and closing timing of the intake valve 8 as shown in FIG. 8. That is, the In-VVT 31 is controlled. Specifically, the proper start control is configured to determine the closing timing of the intake valve 8 based on the required air load factor during fuel cut (FC) in addition to the engine water temperature and engine speed. That is, the required braking force caused by the engine 1 being rotated is determined by the fuel cut control before the engine is started, and the closing timing of the intake valve 8 is determined based on the required air load factor for generating the required braking force. Here, the lower the required air load factor is, the earlier (advanced) the closing timing of the intake valve 8 is configured. Note that the proper start control only requires that at least one of the fuel injection amount, the ignition timing, and the closing timing can be controlled based on the intake air amount.

As described above, when the rotation speed of engine 1 is higher than a predetermined rotation speed, the fuel injection amount, ignition timing, or valve closing timing is controlled based on the amount of air supplied to engine 1. Therefore, when a request to start engine 1 is made while engine 1 is rotating at a high rotation speed, starting performance can be improved by setting the air-fuel ratio of engine 1 to an appropriate air-fuel ratio, setting the ignition timing to an appropriate timing to increase the combustion speed, or improving combustion efficiency.

The internal combustion engine start control device in the embodiment of the present invention may be intended for a vehicle that uses an internal combustion engine as its only driving force source, or may be intended for a hybrid vehicle that is equipped with a motor as a driving force source in addition to an internal combustion engine.

REFERENCE SIGNS LIST 1 engine 2 cylinder 8 intake valve 10 exhaust valve 12 air flow meter 20, 21 A/F sensor 25 direct injection injector 26 port injection injector 31 variable valve timing mechanism (In-VVT)
32 Variable valve timing mechanism (Ex-VVT)
36 Water temperature sensor 38 Ignition device 39 Ignition coil 48 Electronic control unit (ECU)

Claims (5)

1. A start control device for an internal combustion engine comprising: a fuel injection device that injects fuel; an intake valve that opens and closes an intake port of a cylinder to which air and the fuel are supplied; and an ignition device that ignites a mixture of the air and the fuel,
a controller for controlling the fuel injection device, the ignition device, and the intake valve;
The controller:
when the rotation speed of the internal combustion engine is equal to or lower than a predetermined rotation speed, a fixed start control is executed to control a fuel injection amount of the fuel injection device, an ignition timing of the ignition device, and a closing timing of the intake valve regardless of an amount of air supplied to the internal combustion engine;
A start control device for an internal combustion engine, characterized in that, when the rotation speed of the internal combustion engine is higher than the predetermined rotation speed, an appropriate start control is executed to control at least one of the fuel injection amount, the ignition timing, and the valve closing timing based on the air amount. 2. A start control device for an internal combustion engine according to claim 1,
The controller:
A start control device for an internal combustion engine, characterized in that when there is a start request to combust the mixture to generate power and the temperature of the internal combustion engine is below a predetermined temperature, either the fixed start control or the appropriate start control is executed. 3. A start control device for an internal combustion engine according to claim 1,
The proper start control includes:
A target value of an equivalence ratio is determined by dividing the theoretical air-fuel ratio by the actual air-fuel ratio;
A target fuel injection amount is calculated by multiplying the target value by the air amount.
A start control device for an internal combustion engine, comprising: a control unit for controlling the fuel injection device based on the target fuel injection amount. 3. A start control device for an internal combustion engine according to claim 1,
The proper start control includes:
13. A start control device for an internal combustion engine, comprising: a start control unit for controlling a start timing of an internal combustion engine, the start timing of the start timing being advanced as the amount of air becomes smaller. 3. A start control device for an internal combustion engine according to claim 1,
The proper start control includes:
2. A start control device for an internal combustion engine, comprising: a start control unit for controlling a start control of an internal combustion engine, the start control unit being configured to advance the valve closing timing as the air amount decreases.

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