JP7365564B2 - engine system - Google Patents

Description

The present invention relates to an engine system, and more particularly, the present invention includes an engine, a main combustion chamber, an auxiliary chamber formed with a communication hole communicating with the main combustion chamber, an injector, and a first ignition starter that ignites the air-fuel mixture in the main combustion chamber. The present invention relates to an engine system including a plug, a second spark plug that ignites an air-fuel mixture in a pre-chamber, and a control device that controls the first spark plug and the second spark plug.

Conventionally, in engines (internal combustion engines), an auxiliary chamber is provided within the main combustion chamber, and flame is ejected into the main combustion chamber from a communication hole in the auxiliary chamber, thereby speeding up the propagation of combustion in the main combustion chamber and improving the thermal efficiency of the engine. Techniques are known that allow this to occur.

For example, Patent Document 1 discloses a main injector that injects fuel into a main combustion chamber, a sub-injector provided on the upstream side of a sub-chamber, and a spark plug provided in the sub-chamber. An engine is disclosed in which the air-fuel mixture in the pre-chamber is ignited by the engine, and the flame of the air-fuel mixture combusted in the pre-chamber is ejected from a nozzle hole into the main combustion chamber, thereby combusting the air-fuel mixture in the main combustion chamber. .

JP2014-227975A

However, in the process of engine research and development, the present inventors discovered that, for example, condensed water contained in exhaust gas in EGR, which recirculates exhaust gas after combustion into the cylinder, and moisture generated during the combustion process, In some cases, we have learned that using an auxiliary chamber to increase thermal efficiency may pose a problem. In other words, while such condensed water and moisture remain in the pre-chamber, for example, when the outside temperature is low, it takes a long time to restart the engine, the engine water temperature decreases, and the combustion chamber temperature decreases accordingly. If the temperature drops, the moisture in the pre-chamber will freeze and block the communication hole, making it difficult for the flame generated in the pre-chamber to blow out into the main combustion chamber, or the moisture in the pre-chamber will adhere to the spark plug in the pre-chamber. They discovered a problem in which phenomena such as failure to discharge and difficulty in ignition occur, and as a result, the original effect of the subchamber, which is to speed up the propagation of combustion in the main combustion chamber and increase thermal efficiency, may not be obtained. It is.

Therefore, the present invention has been made to solve the above-mentioned problems, and provides an engine system that can reliably combust the air-fuel mixture in the main combustion chamber in an engine provided with a pre-chamber even when the engine water temperature is low. The purpose is to provide

In order to achieve the above object, the present invention provides an engine, a piston that reciprocates within the cylinder of the engine, a main combustion chamber formed by the cylinder head and the piston of the engine, and a main combustion chamber provided in the main combustion chamber of the engine. an auxiliary chamber formed with a communication hole that communicates with the main combustion chamber; an injector that is installed in the engine and injects fuel into the main combustion chamber; a first spark plug that ignites the engine; a second spark plug that is installed in the subchamber of the engine and ignites the air-fuel mixture in the subchamber; a coolant temperature detector that detects the temperature of the engine coolant; a control device that receives an output signal from the injector and controls the first spark plug and the second spark plug, the injector is provided on the axis of the cylinder, and the subchamber and the second spark plug are connected to the injector. The control device includes a cooling water temperature determination means for determining whether the temperature of the engine cooling water detected by the cooling water temperature detector is below a predetermined threshold value. , the control device is configured to control the first spark plug so as to cause the first spark plug to ignite when the engine cooling water temperature is determined to be below a predetermined threshold by the cooling water temperature determining means. It is characterized by the fact that there is.

According to the present invention configured in this manner, the combustion in the pre-chamber and the ejection of flame from the communication hole are prevented by EGR condensed water adhering to the sub-chamber and its communication hole and moisture generated during combustion. Even if the engine cooling water temperature is below a predetermined temperature/below a predetermined threshold, the first spark plug facing the main combustion chamber ignites the air-fuel mixture in the main combustion chamber, which ignites the air-fuel mixture in the main combustion chamber. It can be burned reliably. That is, even when the engine water temperature is low, the air-fuel mixture in the main combustion chamber can be reliably combusted in the engine provided with the auxiliary chamber.
Further, according to the present invention configured in this way, it is possible to suppress the temperature of the pre-chamber from excessively increasing due to heat from the exhaust gas, and as a result, it is possible to stably burn the air-fuel mixture in the pre-chamber. can.

Further, in the present invention, preferably, the control device is configured to control the second spark plug to cause the second spark plug to ignite when it is determined that the engine cooling water temperature exceeds a predetermined threshold. There is.
According to the present invention configured in this manner, the combustion in the pre-chamber and the ejection of flame from the communication hole are prevented by EGR condensed water adhering to the sub-chamber and its communication hole and moisture generated during combustion. When the engine cooling water temperature exceeds (when the water temperature exceeds a predetermined threshold), the temperatures of the main combustion chamber and the pre-chamber are also rising, so it is possible to burn the air-fuel mixture in the pre-chamber by igniting the second spark plug. become. Therefore, the combustion in the pre-chamber caused by the second spark plug causes flame to be ejected from the communication hole in the pre-chamber, making it possible to hasten the propagation of combustion in the main combustion chamber, thereby increasing the thermal efficiency of the engine.

Further, in the present invention, preferably, the control device controls the first spark plug to cause ignition by the first spark plug when the engine cooling water temperature is determined to be below a predetermined threshold value and when the engine is started. configured to control.
According to the present invention configured in this way, when starting the engine when there is a possibility that condensed water or moisture has adhered to the sub-chamber or the communication hole, the first spark plug is used to ignite the engine, so the second spark plug in the sub-chamber is ignited. The air-fuel mixture in the main combustion chamber can be reliably combusted by the first ignition plug while preventing misfires caused by this.

Further, in the present invention, preferably, in the engine, the first spark plug is provided on the exhaust port side of the engine.

According to the engine system of the present invention, even when the engine water temperature is low, the air-fuel mixture in the main combustion chamber can be reliably combusted in the engine provided with the auxiliary chamber.

1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. 1 is a sectional view showing a schematic configuration around a main combustion chamber formed in a cylinder of an engine in an engine system according to the present embodiment. 1 is a plan view of a schematic configuration around a main combustion chamber formed in a cylinder of an engine in an engine system according to the present embodiment, viewed from above in the cylinder axis direction. 4(a) is a partial cross-sectional view of the sub-chamber and sub-spark plug of the pre-chamber plug as seen from the side, and FIG. 4(b) is a diagram showing the pre-chamber plug according to the present embodiment. FIG. 3 is a plan view of the subchamber of the plug, viewed from below in the axial direction. FIG. 1 is a control block diagram of an engine control device according to an embodiment of the present invention. It is an engine control map set according to engine load and engine rotation speed by the engine control device according to the embodiment of the present invention. 7 is a time chart of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention, and is a diagram illustrating an example of the time chart in a low-medium load region in the engine control map shown in FIG. 6. FIG. 7 is a time chart of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention, and is a diagram illustrating an example of the time chart in a high load low rotation region in the engine control map shown in FIG. 6. FIG. 7 is a time chart of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention, and is a diagram showing an example of the time chart in a high load, high rotation region in the engine control map shown in FIG. 6. FIG. 7 is a time chart of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention, in which the fuel injection timing is changed according to the engine load in the high-load, high-speed region in the engine control map shown in FIG. 6. It is a figure which shows an example of the time chart for demonstrating. 5 is a flowchart showing details of engine control based on an engine control map by the engine control device according to the embodiment of the present invention. 7 is a flowchart showing the details of engine control executed when the engine is started according to the control map shown in FIG. 6; 13 is a time chart showing control details of the main spark plug and the auxiliary spark plug, which are switched according to the engine water temperature, determined based on the flowchart shown in FIG. 12. FIG.

Hereinafter, an engine system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First, with reference to FIG. 1, a schematic configuration of an engine system according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention.

As shown in FIG. 1, an engine system 1 includes a multi-cylinder (in this embodiment, four cylinders) engine (internal combustion engine) 2 that generates power for a vehicle by burning a mixture of intake air and fuel; The engine 2 includes an intake passage 4 for introducing intake air into the engine 2, and an exhaust passage 6 for discharging exhaust gas from the engine 2. Note that the present invention is applicable not only to four-cylinder engines but also to other engines such as six-cylinder engines.

Each cylinder of the engine 2 includes an intake port 8 connected to the intake passage 4 and formed in a cylinder head 54 (see FIG. 2) described later, an intake valve 10 provided in the intake port 8, and an exhaust passage 6. An exhaust port 12 connected to the cylinder head 54 and an exhaust valve 14 provided in the exhaust port 12 are provided.
The intake valve 10 is provided with a variable valve lift mechanism (Sequential Valve Timing) 16 that electrically variably controls the lift amount and opening/closing timing of the intake valve 10.
Similarly, the exhaust valve 14 is also provided with a variable valve lift mechanism 18 that makes the lift amount and opening/closing timing of the exhaust valve 14 variable.

The engine 2 includes a piston 24 that reciprocates within a cylinder 22 by a crankshaft 20, and a combustion chamber (main combustion chamber) 26 is formed by this piston 24 and a cylinder head 54 (see FIG. 2). ).
The main combustion chamber 26 is provided with an injector 28 that injects combustion into the main combustion chamber 26, a pre-chamber plug 30, which will be described later, and a main spark plug 32, each facing into the main combustion chamber 26. ing.

On the upstream side of the intake passage 4, there is an air cleaner 34 and a throttle valve that is electrically operated and adjusts the amount of intake air passing therethrough based on the required fuel injection amount based on the driver's accelerator opening and a command signal from the ECU 50, which will be described later. An intake throttle valve) 36 and a surge tank 38 for temporarily storing intake air to be supplied to the engine 2 are provided.
A three-way catalyst 40 for purifying exhaust gas is provided on the downstream side of the exhaust passage 6.
Further, the exhaust passage 6 is connected to an EGR passage 42 that circulates a portion of the exhaust gas that has passed through the three-way catalyst 40 to the intake passage 4. The EGR passage 42 is provided with an EGR cooler 44 and an EGR valve 46 that controls the flow rate of exhaust gas flowing through the EGR passage 42.

Further, the engine system 1 includes an ECU (Electronic Control Unit) 50 that controls the engine 2. This ECU 50 corresponds to an "engine control device" in the present invention, and in this embodiment, the operation of the engine 2 (fuel injection timing, ignition timing, air-fuel ratio, etc.). Specifically, control of the fuel injection timing of the injector 28 and the ignition timing of the spark plugs 30 and 32, which will be described below, is executed by a circuit within the ECU 50.

Next, a schematic configuration around the main combustion chamber 26 of the engine 2 will be described with reference to FIGS. 2 and 3. FIG. 2 is a sectional view showing a schematic configuration around the main combustion chamber formed in the cylinder of the engine according to the present embodiment, and FIG. 3 is a schematic diagram showing the structure around the main combustion chamber formed in the cylinder of the engine according to the present embodiment FIG. 3 is a plan view of the configuration viewed from above in the cylinder axis direction. Note that FIGS. 2 and 3 show a schematic configuration around the main combustion chamber of one cylinder among multiple cylinders. The other cylinders are similarly configured.

First, as shown in FIG. 2, the engine 2 includes a cylinder block 52 and a cylinder head 54.
A cylinder 22 is formed in the cylinder block 52 . A connecting rod 21 connected to the crankshaft 20 is connected to a piston 24 provided within the cylinder 22, so that the piston 24 reciprocates within the cylinder 22.

Next, as shown in FIGS. 2 and 3, two independent intake ports 8 (8a, 8b) and two exhaust ports 12 are formed in the cylinder head 54 for each cylinder 22. There is. Although not shown in FIGS. 2 and 3, the intake ports 8a, 8b and the exhaust port 12 are provided with the above-mentioned intake valve 10 and exhaust valve 14, respectively, to open and close the opening on the main combustion chamber 26 side. It is provided.

An intake passage 4a connected to one of the two intake ports 8a and 8b is provided with a swirl control valve 56 that adjusts the opening degree of the intake passage 4a. A swirl flow is generated in the main combustion chamber 26 with a strength corresponding to the opening degree of the swirl control valve 56. The greater the strength of this swirl flow, the more easily the swirl flow of the air-fuel mixture circulating within the main combustion chamber 26 flows toward the outer periphery of the main combustion chamber 26 and the piston 24.

Next, as shown in FIG. 2, an injector 28, a prechamber plug 30, and a main spark plug 32 are attached to the cylinder head 54.
As shown in FIGS. 2 and 3, the injector 28 is provided on the cylinder axis, and is provided so as to face the center of the main combustion chamber 26 when the main combustion chamber 26 is viewed from above.

Further, the pre-chamber plug 30 is provided on the intake port 8 side with respect to the injector 28, and is arranged so as to extend diagonally downward from the intake port 8 side and face the main combustion chamber 26, as shown in FIG. has been done.
In this embodiment, as shown in FIG. 3, the tip of the pre-chamber plug 30 facing the main combustion chamber 26 (the part indicated by the broken line 30 in FIG. 3) has two intake ports 8a and 8b in plan view. It is located at an intermediate position. Note that a sub-chamber 60 and a sub-spark plug 62 are provided at the tip of the pre-chamber plug 30, as will be described later.

In this embodiment, the auxiliary chamber 60 and the auxiliary spark plug 62 are provided on the intake port 8 side in this way to prevent the auxiliary chamber 60 from receiving heat from the exhaust gas and the temperature inside the auxiliary chamber 60 from rising excessively. I'm trying to suppress it. This speeds up the propagation of combustion within the auxiliary chamber 60 and prevents the flame from ejecting from the communication hole 66 into the main combustion chamber 26 from becoming stronger.

In addition, in this embodiment, as shown in FIGS. 2 and 3, the tip of the pre-chamber plug 30 is located in an area on the outer circumferential side of the main combustion chamber 26 (at least in an area on the outer circumferential side from the openings of the intake and exhaust ports 8 and 12). area) in the central area.

Further, the main spark plug 32 is provided on the exhaust port 12 side with respect to the injector 28, and as shown in FIG. 2, the main spark plug 32 extends diagonally downward from the exhaust port 12 side and It is arranged so as to face the room 26.
In this embodiment, as shown in FIG. 3, the tip of the main spark plug 32 facing the main combustion chamber 26 is provided at a position midway between the two exhaust ports 12 in plan view. Furthermore, a portion 32 indicated by a broken line in FIG. 3 indicates the positions of the center electrode 32a and the side electrode (ground) 32b (see FIG. 2) at the tip of the main spark plug 32.

Next, the prechamber plug 30 will be explained with reference to FIG. FIG. 4 is a diagram showing the pre-chamber plug according to the present embodiment, and FIG. 4(a) is a partial cross-sectional view of the sub-chamber and sub-spark plug of the pre-chamber plug as seen from the side, and FIG. 4(b) FIG. 2 is a plan view of the subchamber of the prechamber plug viewed from below in the axial direction.
First, as shown in FIG. 4(a), the pre-chamber plug 30 has a sub-chamber 60 formed at its tip, and a sub-spark plug 62 is provided within the sub-chamber 60.
The auxiliary spark plug 62, like the main spark plug 32, has a center electrode 62a and a side electrode (ground) 62b.

The auxiliary chamber 60 is provided within the main combustion chamber 26, but is capable of combusting the air-fuel mixture within the auxiliary chamber 60 independently of the main combustion chamber 26. More specifically, it functions as an auxiliary combustion chamber that ignites the air-fuel mixture in the auxiliary chamber 60 with the auxiliary spark plug 62 to cause flame propagation within the auxiliary chamber 60 .

Next, as shown in FIGS. 4(a) and 4(b), the sub-chamber 60 is formed by a hemispherical sub-chamber forming part 64 having a predetermined diameter and thickness (in this embodiment, a radius of 5 mm and a thickness of 1 mm). It is formed by A plurality of communication holes (nozzle holes) 66 communicating with the main combustion chamber 26 are formed in the sub-chamber forming portion 64 .

These communication holes 66 are provided, firstly, to allow the air-fuel mixture in the main combustion chamber 26 to flow into the auxiliary chamber 60, and secondly, to ignite the air-fuel mixture that has flowed in by the auxiliary spark plug 62. It is provided to cause the combustion propagation generated in the subchamber 60 to be ejected/radiated into the main combustion chamber 26 as a flame, thereby speeding up the combustion propagation of the air-fuel mixture in the main combustion chamber 26.
The mixture is basically a mixture of fresh air from the intake port 8 and fuel injected from the injector 28 when the EGR valve 46 is closed, and when the EGR valve 46 is open. is a mixture of fresh air from the intake port 8, exhaust gas from the EGR passage 42, and fuel injected from the injector 28.

In this embodiment, three of these communication holes 66 are provided at 120° intervals around the axis passing through the apex A of the sub-chamber forming portion 64 in a plan view from below as shown in FIG. 4(b). The diameter of each is 1.2 mm. Further, as shown in FIG. 4(a), the communication holes 66 are each formed to extend in a 45° direction at a position of 45° from the apex A of the sub-chamber forming portion 64 when viewed from the side. , flame is ejected from the communication hole 66 at an angle of 45° with respect to its axis.

As will be described later, the number, diameter, and position of the communication holes 66 are not limited to these values. For example, two communication holes 66 may be provided at 180° intervals and have a diameter of 1.0 mm when viewed from below. It's okay. In this way, by reducing the number and/or diameter of the communication holes 66, the flame ejected from the communication holes 66 into the main combustion chamber 26 can be made stronger. In addition, when the ejected flame is strengthened in this way, the combustion propagation within the main combustion chamber 26 becomes faster, so the air-fuel mixture within the main combustion chamber 26 is made leaner and the thermal efficiency of the engine 2 is improved. can be increased.

Further, the number and diameter of the communication holes 66 can be changed in advance when setting a threshold value of the engine rotation speed in an engine control map to be described later. In other words, by changing the number and diameter of the communication holes 66, it is possible to change the appropriate threshold value of the engine rotation speed in the engine control map.

Next, a control block of the engine control device according to the embodiment of the present invention will be explained with reference to FIG. FIG. 5 is a control block diagram of the engine control device according to the embodiment of the present invention.
As shown in FIG. 5, the ECU 50 (see FIG. 1) that controls the engine system 1 includes a microcomputer, memory, I/F circuit, etc. (not shown), and receives an ignition signal SW1 and signals from various sensors SW2 to SW10. Based on the output signal, the fuel injection timing, ignition timing, air-fuel ratio, swirl strength, etc. of the engine 2 are controlled as described later. Note that the sensors SW2 to SW10 are well-known and are not shown in FIGS. 1, 2, etc.

Specifically, the ECU 50 receives an ignition output signal (SW1) indicating a command to start the engine, an output signal regarding the intake air amount from the air flow sensor SW2 provided in the intake passage 4, and an intake air temperature provided in the intake passage 4. An output signal related to the intake air temperature from the sensor SW3, an output signal related to the intake pressure from the intake pressure sensor SW4 provided in the intake passage 4, an output signal related to the coolant temperature from the coolant temperature sensor SW5 provided in the cylinder head 54, An output signal related to the crank angle from the crank angle sensor SW6 provided on the crankshaft 20, an output signal related to the accelerator pedal opening from the accelerator opening sensor SW7, an intake cam angle provided on the intake camshaft (not shown) An output signal related to the intake side cam angle from sensor SW8, an output signal related to the exhaust side cam angle from exhaust cam angle sensor SW9 provided on the exhaust camshaft (not shown), and an output signal related to the exhaust side cam angle provided on the cylinder head 54. Output signals related to the combustion pressure within the main combustion chamber 26 from the fuel pressure sensor SW10 are respectively input.

Here, the output signal regarding the opening degree of the accelerator pedal is a signal that outputs a numerical value corresponding to the amount by which the driver has depressed the accelerator pedal, and this signal is used in the ECU 50 to determine the driver's requested torque and to The engine load of engine 2 (target output torque/target engine torque) is determined based on the required torque of ``load range'' and ``engine high load range above a predetermined rotation speed'').

The ECU 50 controls fuel injection timing by the injector 28 based on these output signals.
The ECU 50 also controls the ignition timing of the main spark plug 32 and the sub-spark plug (PCP spark plug) 30 in the pre-chamber plug 30.
Further, the ECU 50 mainly controls the intake air amount to the main combustion chamber 26 by controlling the intake side variable valve lift mechanism (intake electric S-VT) 16 and the throttle valve 36, and also controls the intake air amount to the main combustion chamber 26. By controlling the fuel injection timing and fuel injection amount by 28, the air-fuel ratio in the main combustion chamber 26 is controlled. In this embodiment, the air-fuel ratio is mainly controlled by controlling the fuel injection timing. In addition, along with this air-fuel ratio control, the exhaust side variable valve lift mechanism (exhaust electric S-VT) 18 and the EGR valve 46 are also controlled, for example, to reduce NOx.
Further, the ECU 50 controls the strength of the swirl flow using a swirl control valve 56.

Next, an engine control map that is used in the engine control device according to the embodiment of the present invention and is set according to the engine load and engine speed will be explained with reference to FIG. FIG. 6 is an engine control map set according to the engine load and engine rotation speed by the engine control device according to the embodiment of the present invention.
This engine control map is stored in the memory of ECU 50, and ECU 50 controls engine 2 based on this control map.
Here, in FIG. 6, the engine load on the vertical axis is the target engine torque, and the horizontal axis is the engine rotation speed. The ECU 50 calculates this target engine torque based on the target engine torque calculated based on the output signal from the accelerator opening sensor SW7 and the rotation speed (rpm) of the engine 2 calculated based on the output signal from the crank angle sensor SW6. The engine 2 is controlled while referring to the control map.
Hereinafter, the engine control settings in the control map referred to by the ECU 50 and the method of controlling the engine 2 by the ECU 50 will be specifically described.

First, as shown in FIG. 6, the engine control map of this embodiment is set so that only the main spark plug 32 ignites when starting the engine.
More specifically, when the ignition output signal SW1 is input to the ECU 50 and it is determined that the engine is to be started, the ECU 50 is set to ignite the air-fuel mixture in the main combustion chamber 26 using the main ignition plug 32. The air-fuel mixture in the main combustion chamber 26 when the engine is started has a stoichiometric air-fuel ratio (λ=1). At this time, the sub-spark plug 62 of the pre-chamber plug 30 does not ignite the inside of the sub-chamber 60.

Next, as shown in FIG. 6, in the engine control map of this embodiment, the main combustion The air-fuel mixture in the chamber 26 is set to the stoichiometric air-fuel ratio (λ=1), and the air-fuel ratio of the air-fuel mixture flowing into the subchamber 60 of the pre-chamber plug 30 is set to the stoichiometric air-fuel ratio. Further, in this region, only the auxiliary spark plug 62 of the pre-chamber plug 30 is set to ignite.

Based on such a control map, when the engine 2 is operating, the ECU 50 determines whether or not the engine 2 is operating in this low-medium load region based on the target engine torque determined by the output signal of the accelerator opening sensor SW7. (See FIG. 11).
If it is determined that the range is within this range, in this embodiment, the ECU 50 mainly controls the fuel injection timing by the injector 28 to control the inside of the main combustion chamber 26 and the auxiliary chamber 60 of the pre-chamber plug 30 at the time of ignition. control so that the air-fuel ratio within is the stoichiometric air-fuel ratio. Further, the ECU 50 controls the timing of igniting the air-fuel mixture in the sub chamber 60 using the sub ignition plug 62. Specific fuel injection timing and ignition timing will be described later.

Next, as shown in FIG. 6, there is a high engine load region that is equal to or higher than a predetermined engine load T1 and a rotation speed region that is less than a predetermined engine rotation speed Re1 (hereinafter referred to as a "high load low rotation region"). In this example, only the main spark plug 32 is set to ignite. In this embodiment, the air-fuel mixture in the main combustion chamber 26 in this region is set to the stoichiometric air-fuel ratio (λ=1). In this region, the sub-spark plug 62 of the pre-chamber plug 30 does not ignite within the sub-chamber 60 .

Based on such a control map, the ECU 50 determines the target engine torque determined by the output signal of the accelerator opening sensor SW7 and the rotation speed ( rpm), it is determined whether the engine 2 is operating in this high-load, high-speed region (see FIG. 11).
If it is determined that the range is within this range, in this embodiment, the ECU 50 mainly controls the fuel injection timing by the injector 28 so that the air-fuel ratio in the main combustion chamber 26 becomes the stoichiometric air-fuel ratio at the time of ignition. control like this. Further, the ECU 50 controls the timing of igniting the air-fuel mixture in the main combustion chamber 26 using the main ignition plug 32. Specific fuel injection timing and ignition timing will be described later.

Next, as shown in FIG. 6, there is a high engine load region that is equal to or higher than a predetermined engine load T1 and a high engine speed region that is equal to or higher than a predetermined engine speed Re1 (hereinafter referred to as a "high load high rotation region"). ), the air-fuel mixture in the main combustion chamber 26 is set to be leaner than the stoichiometric air-fuel ratio (λ>1), and the air-fuel ratio of the air-fuel mixture flowing into the auxiliary chamber 60 of the pre-chamber plug 30 is set to a leaner air-fuel ratio than the stoichiometric air-fuel ratio (λ>1). The air-fuel ratio is set to be leaner than the air-fuel ratio (λ>1). Further, in this high load, high rotation range, only the sub-spark plug 62 of the pre-chamber plug 30 is set to ignite.

Based on such a control map, when the engine 2 is operating, the ECU 50 determines whether or not the engine 2 is operating in this high-load, high-speed range based on the target engine torque determined by the output signal of the accelerator opening sensor SW7. (See FIG. 11).
If it is determined that the region is within this range, in this embodiment, the ECU 50 mainly controls the fuel injection timing by the injector 28 to control the air in the main combustion chamber 26 and the auxiliary chamber 60 of the pre-chamber plug 30. The fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. Further, the ECU 50 controls the timing of igniting the air-fuel mixture in the sub chamber 60 using the sub ignition plug 62. Specific fuel injection timing and ignition timing will be described later.

Here, in the present embodiment, in the control map shown in FIG. The load (target engine torque) T1 is set to 70% (T1=70%) when the maximum engine load is 100%. Note that as a modification, a value other than 70% may be set depending on the engine specifications and the like.

Further, in the present embodiment, in the control map shown in FIG. 6, a predetermined engine rotation speed Re1, which is the boundary between the high load low rotation area and the high load high rotation area, is set to 3000 rpm. In addition, as a modification, the engine rotational speed serving as this boundary may be set to 1000 rpm, for example, depending on the number and diameter of the communication holes 66 of the subchamber 60 described above.

Next, fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention will be explained with reference to FIGS. 7 to 10. 7 to 10 are examples of time charts of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention, and FIG. FIG. 8 is a diagram showing an example of a basic time chart in the high load low rotation region in the engine control map shown in FIG. 6, and FIG. 10 is a diagram showing an example of a time chart in a high-load, high-speed region in the engine control map shown in FIG. 6, and FIG. 10 shows timings of fuel injection timing and ignition timing controlled by the engine control device according to the embodiment of the present invention. 7 is a chart showing an example of a time chart for explaining a change in fuel injection timing according to engine load in a high load, high rotation region in the engine control map shown in FIG. 6. FIG.

First, as shown in FIG. 7, in this embodiment, batch fuel injection is performed at a predetermined timing in the middle of the intake stroke (crank angle=-300° to -240°) in the low-medium load region. Note that such fuel injection timing is not limited to the middle of the intake stroke, but can also be from a predetermined timing at the beginning of the intake stroke to a predetermined timing at the middle of the intake stroke, or from a predetermined timing at the middle of the intake stroke to a predetermined timing at the end of the intake stroke. During the period up to the timing of , fuel and air are mixed in the intake stroke to make the air-fuel mixture at the stoichiometric air-fuel ratio, and in the compression stroke, the air-fuel mixture at the stoichiometric air-fuel ratio can be caused to flow into the pre-chamber 60. It's fine if it's the right time.

In addition, as shown in FIG. 7, in this low-medium load region, the ignition of the air-fuel mixture in the auxiliary chamber 60 by the auxiliary ignition plug 62 of the pre-chamber plug 30 (hereinafter referred to as "PCP ignition") is This is done in the latter half of the compression stroke, before the point.

In this way, in this embodiment, the fuel is basically injected at once in the middle of the intake stroke, and the fuel and air are mixed in the latter half of the intake stroke to make the air-fuel mixture homogeneous. , an air-fuel mixture having a stoichiometric air-fuel ratio of λ=1 is formed, and then, in the compression stroke, the air-fuel mixture having the stoichiometric air-fuel ratio is caused to flow into the subchamber 60 of the pre-chamber plug 30. When the set ignition timing is reached, the air-fuel mixture that has entered the sub-chamber 60 is ignited by the sub-ignition plug 62, and the flame propagation generated within the sub-chamber 60 is ejected/radiated into the main combustion chamber 26 as flame. , thereby speeding up the flame propagation of the air-fuel mixture within the main combustion chamber 26.

Next, as shown in FIG. 8, in this embodiment, fuel is injected at a predetermined time in the middle of the intake stroke in the high load and low rotation region, and further at a predetermined time in the latter half of the compression stroke immediately before the ignition timing. Inject fuel. In this embodiment, this fuel injection timing is set within the latter half of the compression stroke immediately before the ignition timing. In this embodiment, such fuel injection timing is a crank angle at which it is assumed that pre-ignition occurs near top dead center immediately before the ignition timing.

In addition, as shown in FIG. 8, in this high-load, low-speed region, the main spark plug 32 ignites the air-fuel mixture in the main combustion chamber 26 (hereinafter referred to as "main plug ignition") around compression top dead center. to be done.

In this way, in this embodiment, the fuel is injected at the latter half of the compression stroke, that is, at the crank angle at which pre-ignition is assumed to occur just before the ignition timing, and the fuel injection causes the main combustion chamber to be injected. By suppressing the temperature rise of 26, the occurrence of pre-ignition is suppressed.
In addition, in this embodiment, since split injection is performed in the compression stroke immediately before the ignition timing, it becomes difficult to secure time for mixing the fuel injected in the compression stroke and the air in the main combustion chamber 26, and accordingly, Since the air-fuel mixture flowing into the auxiliary chamber 60 becomes too lean and tends to misfire, the main ignition plug 32 is used to ignite the air-fuel mixture in the main combustion chamber 26 to ensure combustion.

Next, as shown in FIG. 9, in this embodiment, in the high-load, high-speed region, fuel is injected at a predetermined timing in the middle of the intake stroke, and then in the middle of the compression stroke (-120° to -60°). Inject fuel at predetermined times. Note that such fuel injection timing is not limited to the middle of the intake stroke and/or the middle of the compression stroke, but is also a timing at which a mixture with a lean air-fuel ratio that can be combusted flows into the pre-chamber 60 at the time of ignition. Good to have.

Further, as shown in FIG. 9, in this high-load, high-speed region, the auxiliary spark plug 62 of the pre-chamber plug 30 ignites the air-fuel mixture in the auxiliary chamber 60 in the latter half of the compression stroke.

In this way, in this embodiment, split injection is performed and a part of the total injection amount is injected into the main combustion chamber 26 during the compression stroke, so the amount of fuel injection in the intake stroke is reduced, and the fuel injection amount is reduced until the ignition timing. The air-fuel mixture in the main combustion chamber 26 that is mixed during this time can be made lean, and such a lean air-fuel mixture can be allowed to flow into the auxiliary chamber 60. In this case, the fuel injected during the compression stroke produces less air-fuel mixture due to the short mixing time, and thus less air-fuel mixture enters the subchamber 60. This also makes it possible to make the air-fuel mixture in the subchamber 60 lean (λ>1). When the auxiliary spark plug 62 ignites the air-fuel mixture in the auxiliary chamber 60, the flame of the combusted air-fuel mixture in the auxiliary chamber 60 is caused by the fact that the air-fuel mixture is lean compared to when the air-fuel mixture is at the stoichiometric air-fuel ratio. Propagation slows down. As the flame propagation within the sub-chamber 60 becomes slower, the force of the flame ejected from the communication hole 66 of the sub-chamber 60 also weakens. In this way, in this embodiment, combustion propagation within the main combustion chamber 26 is slowed down in the high-load, high-speed region.

In other words, in this high-load, high-speed region, by making the air-fuel mixture in the sub-chamber 60 lean, flames are prevented from ejecting vigorously from the sub-chamber 60. As a result, in this embodiment, combustion propagation in the main combustion chamber 26 becomes abnormally fast, and high-frequency air column resonance (1.5 kHz, 3 to 4 kHz, 6 to 7 kHz) occurs in the space (air column) of the main combustion chamber 26. The system is designed to suppress abnormal combustion that would cause vibrations in the surrounding areas.

Next, as shown in FIG. 10, in the high-load, high-speed region, the fuel injection timing is changed according to the engine load (target engine torque). More specifically, in this embodiment, the fuel injection timing in the intake stroke is not changed, but the fuel injection timing in the compression stroke is retarded as the engine load increases. More specifically, in this embodiment, when the engine load is T1 = 70%, which is the boundary between the low and medium load region, fuel is injected at the fuel injection timing as shown by F1 in FIG. Thereafter, as the engine load increases, the fuel injection timing is retarded to the point indicated by F2 in FIG. In this manner, in the present embodiment, in the high-load, high-speed region, as the engine load increases, the fuel injection timing is retarded from the middle of the compression stroke to the latter half of the compression stroke.

In addition, in this high-load, high-speed region, the timing of ignition of the air-fuel mixture in the pre-chamber 60 is retarded according to the engine load in the same manner as the above-mentioned fuel injection timing. It is delayed towards the period around the point.

Further, in this high-load, high-speed region, the swirl control valve 56 shown in FIG. 3 is controlled so that the swirl flow within the main combustion chamber 26 becomes stronger.
In this embodiment, the stronger the swirl flow in the main combustion chamber 26, the more the air-fuel mixture flows toward the outer periphery of the main combustion chamber 26 and the piston 24, and becomes less likely to flow into the central region of the main combustion chamber 26 and the piston 24. We are using. Here, in this embodiment, as described above, the subchamber 60 of the prechamber plug 30 is provided in the central region of the main combustion chamber 26 in plan view (see FIG. 3). Therefore, in this embodiment, by making the swirl flow in the main combustion chamber 26 stronger, the air-fuel mixture becomes difficult to flow into the central region, and accordingly flows into the subchamber 60 provided in the central region. I try to keep the mixture lean.

Next, with reference to FIG. 11, the details of control of the engine 2 by the ECU 50 based on the engine control map shown in FIG. 6 will be explained. FIG. 11 is a flowchart showing details of engine control based on an engine control map by the engine control device according to the embodiment of the present invention. Note that in FIG. 11, S indicates each step.

First, as shown in FIG. 11, in S1, the ECU 50 reads the output signal from the accelerator opening sensor SW7 and the output signal from the crank angle sensor SW6.
Next, in S2, the target engine torque T1 is calculated based on the output signal from the accelerator opening sensor SW7, and then, in S3, the engine rotation speed is calculated based on the output signal from the crank angle sensor SW6. do.
Next, in S4, it is determined whether the target engine torque calculated in S2 is less than a predetermined value. In this embodiment, the predetermined value of the target engine torque in S4 is set to 70%, as described above.

In S4, if the target engine torque is less than the predetermined value (70%) (YES in S4), it is determined that the target engine torque is in the above-mentioned low-medium load region, and the process proceeds to S5. Perform PCP ignition with the mixture.
On the other hand, if the target engine torque is equal to or higher than the predetermined value (70%) in S4 (NO in S4), the process proceeds to S6, and it is determined whether the engine speed calculated in S3 is less than the predetermined value. In this embodiment, the predetermined value of the engine rotation speed in S5 is set to 3000 rpm, as described above.

In S6, if the target engine torque is less than the predetermined value (70%) (YES in S6), it is determined that the target engine torque is in the above-mentioned high load low rotation region, and the process proceeds to S7, in which the main spark plug 32 is The air-fuel mixture in the main combustion chamber 26 is ignited.
On the other hand, in S6, if the target engine torque is equal to or higher than the predetermined value (70%) (NO in S6), it is determined that the target engine torque is in the above-mentioned high-load, high-speed region, and the process proceeds to S8, in which λ Perform PCP ignition with a mixture of >1.

Next, with reference to FIGS. 12 and 13, details of engine control executed at engine startup will be described. FIG. 12 is a flowchart showing the engine control contents executed at the time of engine startup according to the control map shown in FIG. 5 is a time chart showing control details of the main spark plug and the sub spark plug.
First, as shown in FIG. 12, in S1, when the ignition signal SW1 is input to the ECU 50, the process proceeds to S2, where the output signal from the coolant temperature sensor SW5 and the output signal from the crank angle sensor SW6 are read.

Next, the process proceeds to S3, and it is determined whether the engine water temperature is below a predetermined temperature based on the output signal from the coolant temperature sensor SW5 read in S2. In this embodiment, the predetermined temperature (threshold value) of the engine water temperature is 10°C.
In S3, if it is determined that the engine water temperature is below the predetermined temperature (YES in S3), the process proceeds to S4 and starts the engine from the engine rotation speed calculated based on the output signal of the crank angle sensor SW6 read in S2. Determine whether it is time.
If it is determined in S4 that the engine is to be started (YES in S4), ignition is performed using only the main spark plug 32, as described above.

On the other hand, if it is determined in S3 that the engine water temperature exceeds the predetermined temperature (NO in S3), the engine 2 is operated to such an extent that there is no freezing or moisture adhering to the auxiliary chamber 60 or the communication hole 66 of the pre-chamber plug 30. Assuming that the engine is sufficiently warmed up, PCP ignition (λ=1) is performed in the low-medium load range described above.
Further, in S4, if it is determined that it is not the time to start the engine (YES in S4), it is assumed that the starting of the engine 2 has been completed, and the PCP ignition (λ=1) in the above-mentioned low-medium load region is performed.

Next, as shown in FIG. 13, the main spark plug 32 ignites the air-fuel mixture in the main combustion chamber 26 (in FIG. 13, the main ignition turns from OFF to ON), causing the engine speed to rise. At this time, if the coolant temperature is below the predetermined temperature (10° C.), the engine 2 starts to complete, and the main spark plug 32 continues to ignite even if the engine 2 is operating normally. (Main ignition ON). Thereafter, when the engine water temperature rises and exceeds 10° C., the PCP ignition (λ=1) in the above-mentioned low-medium load region is switched.

In this way, in this embodiment, EGR condensed water adhering to the auxiliary chamber 60 and its communication hole 66 and moisture generated during combustion are prevented from interfering with combustion in the auxiliary chamber 60 and flame ejection from the communication hole 66. The predetermined engine cooling water temperature is set at a temperature exceeding 10°C. Therefore, in this embodiment, when the engine cooling water temperature exceeds 10° C., the auxiliary spark plug 62 combusts the air-fuel mixture in the auxiliary chamber 60 and the flame is ejected from the communication hole 66. The combustion propagation is accelerated to increase the thermal efficiency of the engine 2. Note that in this embodiment, the threshold value of the engine cooling water temperature is set at 10° C., but it can be changed as appropriate depending on the specifications of the engine and the like.

Next, the main effects of the engine control device according to the embodiment of the present invention will be explained.
First, the control unit (ECU) 50 of the engine 2 of the engine system 1 according to the embodiment of the present invention causes the main spark plug 32 to ignite the engine when the engine cooling water temperature is below a predetermined temperature (10° C. in this embodiment). Therefore, the engine cooling water temperature is such that the EGR condensed water adhering to the subchamber 60 and its communication hole 66 and the moisture generated during combustion prevent combustion in the subchamber 60 and flame ejection from the communication hole 66 (in this implementation). Even if the temperature is below 10°C), the main ignition plug 32 facing the main combustion chamber 26 and igniting the air-fuel mixture in the main combustion chamber 26 ignites it, so the air-fuel mixture in the main combustion chamber 26 can be reliably combusted. I can do it. That is, even when the engine water temperature is low, the air-fuel mixture in the main combustion chamber 26 can be reliably combusted in the engine 2 provided with the auxiliary chamber 60.

On the other hand, in this embodiment, when the cooling water temperature of the engine 2 exceeds a predetermined temperature, the control device 50 of the engine 2 of the engine system 1 causes ignition by the sub-spark plug 62 of the pre-chamber plug 30. The engine cooling water temperature is set so that EGR condensed water adhering to 60 and its communication hole 66 and moisture generated during combustion do not interfere with combustion in the subchamber 60 and flame ejection from the communication hole (in this embodiment, 10°C). Since the temperatures of the main combustion chamber 26 and the auxiliary chamber 60 are also rising, the air-fuel mixture in the auxiliary chamber 60 can be ignited by the ignition of the auxiliary spark plug 62. Therefore, combustion in the auxiliary chamber 60 by the auxiliary spark plug 62 causes flame to be ejected from the communication hole 66 of the auxiliary chamber 60, and combustion propagation within the main combustion chamber 26 can be accelerated, resulting in the thermal efficiency of the engine 2. can be increased.

Further, in this embodiment, the control device 50 of the engine 2 of the engine system 1 causes the main spark plug 32 to ignite the engine when starting the engine when there is a possibility that condensed water or moisture may be attached to the subchamber 60 or the communication hole 66. Therefore, the air-fuel mixture in the main combustion chamber 26 can be reliably combusted by the main ignition plug 32 while preventing misfire caused by the auxiliary ignition plug 62 in the auxiliary chamber 60.

Further, according to the present embodiment, in the engine 2, the main spark plug 32 is provided on the exhaust port 12 side, and the auxiliary chamber 60 and the auxiliary spark plug 62 are provided on the intake port 8 side. Therefore, it is possible to prevent the sub-chamber 60 from receiving the heat of the exhaust gas and the temperature within the sub-chamber 60 from increasing excessively, thereby speeding up the propagation of combustion within the sub-chamber 60 and, accordingly, It is possible to suppress the momentum of the flame ejected from the communication hole 66 into the main combustion chamber 26 from becoming strong.

1 Engine system 2 Engine 8 Intake port 10 Intake valve 12 Exhaust port 14 Exhaust valves 16, 18 Variable valve lift mechanism 22 Cylinder
24 Piston 26 Main combustion chamber 30 Pre-chamber plug (second spark plug)
32 Main spark plug (first spark plug)
50 ECU (engine control unit)
52 Cylinder block 54 Cylinder head 56 Swirl control valve 60 Sub-chamber 62 of pre-chamber plug (PCP) Sub-spark plug (second spark plug)
66 Communication hole/nozzle hole

Claims (4)

engine and
A piston that reciprocates within the cylinder of this engine,
a main combustion chamber formed by the cylinder head of the engine and the piston ;
a sub-chamber provided in the main combustion chamber of the engine and having a communication hole communicating with the main combustion chamber;
an injector provided in the engine and injecting fuel into the main combustion chamber;
a first spark plug provided in the engine, facing the main combustion chamber and igniting the air-fuel mixture in the main combustion chamber;
a second spark plug that is provided in the subchamber of the engine and ignites the air-fuel mixture in the subchamber;
a cooling water temperature detector that detects the temperature of the cooling water of the engine;
a control device that receives an output signal from the cooling water temperature detector and controls the first spark plug and the second spark plug;
The injector is provided on the axis of the cylinder,
The subchamber and the second spark plug are provided on the intake port side of the engine with respect to the injector,
The control device has a cooling water temperature determining means for determining whether the temperature of the engine cooling water detected by the cooling water temperature detector is below a predetermined threshold;
The control device controls the first spark plug to cause ignition by the first spark plug when the coolant temperature of the engine is determined to be below a predetermined threshold by the coolant temperature determining means. An engine system comprising: The control device is configured to control the second spark plug to cause the second spark plug to ignite when it is determined that the cooling water temperature of the engine exceeds the predetermined threshold. 1. The engine system according to 1. The control device is configured to control the first spark plug so that it is determined that the cooling water temperature of the engine is equal to or lower than the predetermined threshold value, and causes the first spark plug to ignite when starting the engine. The engine system according to claim 1 or claim 2, wherein the engine system comprises: 4. The engine system according to claim 1, wherein in the engine , the first spark plug is provided on an exhaust port side of the engine.

Images