JP7583565B2 - Internal combustion engine - Google Patents

Description

The present invention relates to a lean-burn internal combustion engine that promotes the temperature rise of an exhaust gas purification catalyst and is equipped with a secondary combustion chamber.

In recent years, lean-burn technology has been attracting attention as one method for improving the thermal efficiency of gasoline engines. This lean-burn technology reduces the amount of fuel put into the combustion chamber to create a lean mixture, which is then burned quickly to improve fuel efficiency.

In lean-burn technology, for example, a pre-chamber combustion method is known to reduce heat loss and exhaust loss, as disclosed in Patent Documents 1 and 2.

In the pre-combustion chamber combustion method, a semicircular cap with multiple tiny holes is placed over an ignition plug placed in the combustion chamber to form a pre-combustion chamber, and a fuel injection device is placed inside this pre-combustion chamber. When a small amount of fuel is injected into the pre-combustion chamber and ignited, the fuel in the pre-combustion chamber burns all at once, and a torch flame is ejected from the multiple tiny holes into the combustion chamber. This torch flame ignites the lean air-fuel mixture in the cylinder, allowing for rapid combustion in a short period of time. This allows for stable combustion in a lean environment and suppresses self-ignition at the bore end.

Japanese Patent Application Publication No. 7-026961 JP 2018-105171 A

In vehicles with internal combustion engine power units, a catalytic converter is installed in the exhaust passage to purify harmful components in the exhaust gas. The catalyst (three-way catalyst) in this catalytic converter is heated by the heat of the exhaust gas to an activation temperature at which it purifies the harmful components.

However, in internal combustion engines using the pre-chamber combustion system, the combustion speed of a lean mixture is fast, making it difficult to quickly heat up the catalyst installed in the exhaust passage, and there is an issue that it takes a long time for the catalyst to reach its activation temperature during cold starts, etc.

In view of the above, the present invention aims to provide an internal combustion engine with pre-chamber combustion that promotes temperature rise to a temperature at which a catalyst installed in the exhaust passage becomes active.

One aspect of the present invention is an internal combustion engine having a cylinder head and a cylinder block,
a cylinder formed in the cylinder block; a piston slidably inserted in the cylinder; a main combustion chamber formed in the cylinder and between the piston and the cylinder head; a plurality of ports formed in the cylinder head so as to communicate with the main combustion chamber, the ports having exhaust valves and intake valves which can be opened and closed; a first chamber and a second chamber each having a sub-combustion chamber and provided in the cylinder head with a bottom facing the piston; a first injector provided in the cylinder head for spraying fuel into the sub-combustion chamber of the first chamber ; a second injector provided in the cylinder head for spraying fuel into the sub-combustion chamber of the second chamber ; a first ignition plug provided in the cylinder head for igniting the mixture in the sub-combustion chamber of the first chamber ; the second injector, the first spark plug, the second injector , the first spark plug, and the second spark plug. The engine control unit controls the first and second injectors to ignite the mixture in the pre-combustion chamber of the first chamber with the first spark plug, and during the exhaust stroke, which is a timing different from the ignition timing of the first ignition plug , the second spark plug ignites the mixture in the pre-combustion chamber of the second chamber into which fuel has been sprayed from the second injector , and injects the torch flame from the nozzle toward the exhaust valve , and sends the torch flame together with combustion gas to the port where the exhaust valve is opened.

The present invention provides an internal combustion engine with pre-chamber combustion that promotes heating to a temperature at which a catalyst installed in the exhaust passage becomes active.

FIG. 1 is a schematic diagram partially showing a cross section of a main part of a lean-burn engine. Partial cross-sectional view showing the state of a lean-burn engine during the intake stroke Partial cutaway view of a lean-burn engine during the compression stroke FIG. 1 is a partial cross-sectional view showing the state of a lean-burn engine at the time of ignition when a torch flame is injected from a first auxiliary combustion chamber. Partial cutaway view of a lean-burn engine during the combustion process FIG. 1 is a partial cross-sectional view showing a state of a lean-burn engine during the exhaust stroke in which a torch flame is injected from a second auxiliary combustion chamber. FIG. 11 is a partial cross-sectional view showing a state of a lean-burn engine at the time of ignition when a torch flame is injected from the second auxiliary combustion chamber of a modified example. FIG. 13 is a partial cross-sectional view showing a state of a lean-burn engine during the exhaust stroke in which a torch flame is injected from the second auxiliary combustion chamber of a modified example.

An embodiment of one aspect of the present invention will be described in detail below with reference to the drawings. Note that in the drawings used in the following description, each component is shown at a different scale so that it can be recognized on the drawing, and the present invention is not limited to the number of components, the shapes of the components, the size ratios of the components, or the relative positions of the components shown in these drawings.

The lean-burn internal combustion engine (hereinafter simply referred to as engine) 1 shown in FIG. 1 is a spark-ignition type direct injection engine, and in this embodiment, for example, a cross section of one cylinder of a naturally aspirated four-cylinder gasoline engine is illustrated.

In the engine 1, a piston 15 is slidably inserted into each cylinder 11 that opens into the cylinder block 10. A piston cavity 15a is formed in the top surface of the piston 15. A main combustion chamber 12 is provided as the space between the piston 15 and the cylinder head 20.

Here, for example, two intake ports 23 and two exhaust ports 24 are opened in the bottom surface 28 of the cylinder head 20 in the region corresponding to each cylinder 11. Furthermore, the two intake ports 23 and the two exhaust ports 24 are provided with intake valves 25 and exhaust valves 26, respectively, for opening and closing them. Note that only one intake port 23 and one exhaust port 24 are shown in FIG. 1.

A first auxiliary combustion chamber unit 40 that functions as a main pre-chamber is provided at approximately the center of the main combustion chamber 12 on the cylinder head 20 side. Furthermore, a second auxiliary combustion chamber unit 41 that functions as a sub-pre-chamber is provided on the exhaust port 24 side of the main combustion chamber 12 on the cylinder head 20 side.

The first auxiliary combustion chamber unit 40 holds a first chamber 42, which is a cylindrical cap body with a bottom, a first ignition plug 47, and a first injector 46 that functions as a fuel injection valve.

The second auxiliary combustion chamber unit 41 holds a second chamber 44, which is a cylindrical cap body with a bottom, a second ignition plug 49, and a second injector 48 that functions as a fuel injection valve.

The ignition parts formed at the tips of the first and second spark plugs 47, 49 and the fuel injection ports provided at the tips of the first and second injectors 46, 48 face the first and second auxiliary combustion chambers 42a, 44a, which are narrow spaces formed by the first and second chambers 42, 44, respectively.

The first chamber 42 has a plurality of nozzles 43 formed in the circumferential direction at its bottom. For example, eight of these nozzles 43 are formed at approximately equal intervals, and the axis of each of these eight nozzles 43 has a predetermined angle θ (for example, θ = 45°) with respect to the central axis of the first chamber 42. In other words, the eight nozzles 43 communicate with the first auxiliary combustion chamber 42a, and the axis of each hole is set so that the openings face radially toward the main combustion chamber 12 with a depression angle.

The second chamber 44 has one or two nozzles 45 formed toward the exhaust valves 26 and exhaust port 24. When there is one nozzle 45, it is preferable that the nozzle 45 is formed toward, for example, approximately the middle of the two exhaust valves 26, and when there are two nozzles, it is preferable that each nozzle 45 is formed toward each exhaust valve 26.

The axis of one or two nozzles 45 also has a predetermined angle θ (e.g., θ = 90°) with respect to the central axis of the second chamber 44. That is, the nozzle 45 communicates with the second auxiliary combustion chamber 44a, and the axis of the nozzle is set so that it faces the exhaust valve 26 side of the main combustion chamber 12.

The cylinder head 20 also holds a third injector 17 that functions as a fuel injection valve for in-cylinder injection, and the fuel injection port of this third injector 17 faces the inside of the cylinder 11 at a predetermined depression angle with respect to the top surface of the piston 15.

The cylinder head 20 is provided with a variable valve mechanism (not shown) that can variably switch the opening state of the intake valve 25 and the exhaust valve 26 for each combustion cycle. The variable valve mechanism can drive the intake valve 25 and the exhaust valve 26 at any timing and lift amount, and is controlled by the engine control unit (ECU) 30.

The ECU 30 is configured around a well-known microcomputer having a CPU, ROM, RAM, an input/output interface, etc., and various sensors/switches including an intake air volume sensor (not shown) and an engine speed sensor that detects the engine speed from the rotation of the crankshaft are connected to the input side.
In addition, the ECU 30 is connected to, for example, a water temperature sensor 31 that detects the temperature of the coolant in a water-cooled engine, an O2 sensor 32 that detects the amount of oxygen in the exhaust gas, and a catalyst temperature sensor 33 that detects the temperature of the catalyst 51 in the catalytic converter 50 or the temperature of the exhaust gas immediately after the catalyst outlet.

The O2 sensor 32 is provided in an exhaust pipe 29 connected to an exhaust manifold 27 that communicates with the exhaust port 24. The catalyst temperature sensor 33 is provided on the rear side of a case body 52 that functions as a protector for the exterior body that houses the catalyst 51 of the catalytic converter 50.

As shown in FIG. 2, the engine 1 configured as described above creates a negative pressure inside the cylinder 11 as the piston 15 descends from the top dead center position, and the intake valve 25 opens in conjunction with the movement of the piston 15, performing an intake stroke in which air (AIR) is drawn into the main combustion chamber 12 from the intake port 23. Then, as shown in FIG. 3, the engine 1 performs a compression stroke in which the piston 15 rises from the bottom dead center position.

During this compression stroke, the engine 1 sprays fuel (gasoline) from the fuel injection port of the third injector 17 into the main combustion chamber 12 under the control of the ECU 30 at a timing according to the required load. Furthermore, the engine 1 sprays fuel (gasoline) from the fuel injection port of the first injector 46 into the first auxiliary combustion chamber 42a at a predetermined timing under the control of the ECU 30.

As shown in FIG. 4, when the piston 15 moves near the top dead center, the engine 1 generates a spark in the ignition section of the first spark plug 47 under the control of the ECU 30, igniting the mixture in the first auxiliary combustion chamber 42a, which is a narrow space.

As a result, the mixture in the first auxiliary combustion chamber 42a combusts rapidly, and eight torch flames F, which serve as ignition sources, are sprayed radially from multiple nozzles 43 (here eight nozzles) into the main combustion chamber 12, performing a combustion process in which the main combustion chamber 12 is rapidly combusted.

As shown in Figure 5, this combustion stroke causes the piston 15 to be pushed down to bottom dead center by the expansion of the combusted gas in the main combustion chamber 12, transmitting power, and the piston 15 then moves from bottom dead center to top dead center due to inertial force.

At this time, as shown in FIG. 6, the exhaust valve 26 of the engine 1 opens in conjunction with the movement of the piston 15, and the exhaust stroke is performed to push the combustion gas (exhaust gas) into the exhaust port 24 outside the cylinder 11.

When engine 1 transitions from the combustion stroke to the exhaust stroke, fuel (gasoline) is sprayed into second auxiliary combustion chamber 44a from the fuel injection port of second injector 48 under the control of ECU 30. Then, at a predetermined timing when exhaust valve 26 opens (for example, the moment exhaust valve 26 opens), engine 1 generates a spark in the ignition part of second ignition plug 49 under the control of ECU 30, igniting the mixture in second auxiliary combustion chamber 44a, which is a narrow space.

As a result, the mixture in the second auxiliary combustion chamber 44a is combusted, and the torch flame F is injected from the nozzle 45 into the main combustion chamber 12 toward the exhaust port 24 with the exhaust valve 26 open. At this time, the torch flame F enters the exhaust port 24 due to the airflow of the combustion gas being swept into the exhaust port 24.

The combustion gas swept into the exhaust port 24 is further heated by the torch flame F, becoming hot, and is then sent to the catalytic converter 50 via the exhaust manifold 27 and exhaust pipe 29 that communicate with the exhaust port 24. This hot combustion gas heats the catalyst 51 of the catalytic converter 50, raising its temperature. As a result, the catalyst 51 is heated by the hot combustion gas, and the time it takes for it to reach an activation temperature at which it purifies the combustion gas is shortened.

As described above, the engine 1 of this embodiment has a configuration in which the combustion chamber has two units, the first and second auxiliary combustion chamber units 40 and 41. Of the two, the first auxiliary combustion chamber unit 40 is the main ignition source that injects a torch flame F, which is a jet flame, into the main combustion chamber 12 to combust the mixture, and the second auxiliary combustion chamber unit 41 is the sub-ignition source that promotes the temperature rise of the catalyst 51 of the catalytic converter 50, which injects the torch flame F directly into the exhaust port 24 in accordance with the timing of the opening of the exhaust valve 26.

In this way, the engine 1 has different ignition timings for the main first pre-combustion chamber unit 40 and the sub second pre-combustion chamber unit 41, and when the catalyst 51 is at a low temperature, the second pre-combustion chamber unit 41 is driven and the torch flame F is injected according to the timing at which the exhaust valve 26 opens. And, because the engine 1 can inject the torch flame F injected from the sub second pre-combustion chamber unit 41 directly into the exhaust system, it is possible to promote the warming up of the catalyst 51.

The ECU 30 controls the operation and stopping of the second auxiliary combustion chamber unit 41 during cold start or under various conditions that promote the temperature rise to a temperature at which the catalyst 51, whose temperature has dropped due to cold climates, etc., is activated. The ECU 30 controls the operation and stopping of the second auxiliary combustion chamber unit 41 based on the detection values of the water temperature sensor 31, O2 sensor 32, catalyst temperature sensor 33, etc.

In addition, because the engine 1 has an independently controlled main first pre-combustion chamber unit 40 and sub second pre-combustion chamber unit 41, the injection of the torch flame F by the first pre-combustion chamber unit 40 is used to ensure combustion stability during warm-up operation (fast idle), and the injection of the torch flame F by the second pre-combustion chamber unit 41 is used to warm up the catalyst 51. This makes it possible to suppress vibrations caused by torque fluctuations due to misfire of the mixture without lowering the temperature of the catalyst 51.

In the above embodiment, the first auxiliary combustion chamber unit 40 sprays fuel (gasoline) directly into the first auxiliary combustion chamber 42a using the first injector 46, and injects the torch flame F into the main combustion chamber 12 by igniting the first spark plug 47. However, the present invention is not limited to this, and a so-called passive mode may be used in which the first injector 46 is not provided, and the mixture that has entered the first auxiliary combustion chamber 42a from each injection port 43 from the main combustion chamber 12 during the compression stroke is injected into the main combustion chamber 12 by igniting the first spark plug 47 to inject the torch flame F.

(Modification)
7 and 8, the engine 1 of this modified example is configured to include only a second pre-combustion chamber unit 41 having the functions of the first pre-combustion chamber unit 40. In other words, the second pre-combustion chamber unit 41 here has the functions of both the main pre-chamber and the sub-pre-chamber.

As shown in FIG. 7, in the engine 1 here, during the combustion stroke, a spark is generated at the ignition section of the second spark plug 49, and the ECU 30 controls the ignition of the mixture in the second auxiliary combustion chamber 44a. As a result, the torch flame F, which is the ignition source, is injected from the nozzle 45 into the main combustion chamber 12, causing the main combustion chamber 12 to combust rapidly and carrying out the combustion stroke.

In addition, the ECU 30 controls the engine 1 to generate a spark in the ignition section of the second spark plug 49 at a predetermined timing when the exhaust valve 26 opens (for example, the moment the exhaust valve 26 opens), thereby igniting the mixture in the second auxiliary combustion chamber 44a.

As a result, the mixture in the second auxiliary combustion chamber 44a is combusted, and as shown in FIG. 8, the torch flame F is injected from the nozzle 45 into the main combustion chamber 12 toward the exhaust port 24 with the exhaust valve 26 open. Therefore, the torch flame F is sent into the exhaust port 24 together with the combustion gas.

Even with this configuration, the engine 1 can reduce the time it takes for the combustion gas, which has been further heated by the torch flame F, to heat the catalyst 51 and reach the activation temperature at which the catalyst 51 purifies the combustion gas, thereby achieving the effects described in the above embodiment.

Furthermore, since the engine 1 only has the second auxiliary combustion chamber unit 41, the structure is simplified and the cost can be reduced. In addition, the engine 1 can increase the diameters of the intake port 23, exhaust port 24, intake valve 25, and exhaust valve 26 on the bottom surface 28 of the cylinder head 20, thereby improving the intake and exhaust efficiency to the cylinder 11.

In the above embodiment and modified example, the engine 1 is configured as a direct injection engine, but the present invention is not limited to this, and the technology can be applied to a port injection engine that injects fuel into the intake pipe to generate an air-fuel mixture.

The ECU 30 has a processor including a central processing unit (CPU), a ROM, a RAM, and other storage devices. In addition, all or part of the configuration of the processor's multiple circuits may be implemented by software. For example, the CPU may read and execute various programs corresponding to each function stored in the ROM.

Furthermore, all or part of the functions of the processor may be configured using logic circuits or analog circuits, and the processing of various programs may be realized using electronic circuits such as FPGAs.

The invention described in the above embodiments is not limited to those embodiments, and various modifications can be made in the implementation stage without departing from the gist of the invention. Furthermore, each of the above embodiments includes inventions at various stages, and various inventions can be extracted by appropriate combinations of the disclosed constituent elements.
For example, if some of the constituent elements shown in each form are deleted, and the stated problem can be solved and the stated effect can be obtained, the configuration from which these constituent elements are deleted can be extracted as an invention.

Reference Signs List 1: Engine 10: Cylinder block 11: Cylinder 12: Main combustion chamber 15: Piston 15a: Piston cavity 17: Third injector 20: Cylinder head 23: Intake port 24: Exhaust port 25: Intake valve 26: Exhaust valve 27: Exhaust manifold 28: Bottom surface 29: Exhaust pipe 30: Engine control unit (ECU)
Reference Signs List 31...water temperature sensor 32...O2 sensor 33...catalyst temperature sensor 40...first auxiliary combustion chamber unit 42...first chamber 42a...first auxiliary combustion chamber 43, 45...nozzle 44...second chamber 44a...second auxiliary combustion chamber 46...first injector 47...first ignition plug 48...second injector 49...second ignition plug 50...catalytic converter 51...catalyst 52...case body F...torch flame

Claims (4)

An internal combustion engine having a cylinder head and a cylinder block,
a cylinder formed in the cylinder block;
A piston slidably inserted in the cylinder;
a main combustion chamber formed within the cylinder between the piston and the cylinder head;
a plurality of ports formed in the cylinder head so as to communicate with the main combustion chamber, the ports having exhaust valves and intake valves that can be opened and closed;
a first chamber and a second chamber each having an auxiliary combustion chamber and provided in the cylinder head such that a bottom portion of the first chamber faces the piston;
a first injector provided in the cylinder head and configured to spray fuel into a sub-combustion chamber of the first chamber ;
a second injector provided in the cylinder head for spraying fuel into a sub-combustion chamber of the second chamber;
a first spark plug provided in the cylinder head for igniting an air-fuel mixture in a sub-combustion chamber of the first chamber ;
a second spark plug provided in the cylinder head for igniting the mixture in the sub-combustion chamber of the second chamber;
a nozzle formed in the second chamber so as to communicate with the auxiliary combustion chamber of the second chamber and to face the exhaust valve side, the nozzle outlet for injecting a torch flame;
an engine control unit that drives and controls the first injector , the second injector, the first spark plug, and the second spark plug ;
Equipped with
the engine control unit executes control to ignite the air-fuel mixture in the pre-combustion chamber of the first chamber with the first spark plug, and during an exhaust stroke, which is a timing different from the ignition timing of the first spark plug, ignite the air-fuel mixture in the pre-combustion chamber of the second chamber, into which fuel has been sprayed from the second injector, with the second spark plug, and inject the torch flame from the nozzle toward the exhaust valve , thereby sending the torch flame together with combustion gas into the port where the exhaust valve is opened. 2. The internal combustion engine according to claim 1 , wherein the engine control unit executes control to ignite the air-fuel mixture in the pre-combustion chamber of the first chamber by the first ignition plug during a combustion stroke , and to ignite the air-fuel mixture in the pre -combustion chamber of the second chamber by the second ignition plug during an exhaust stroke , thereby injecting the torch flame. 3. An internal combustion engine according to claim 1 , wherein the nozzle hole axis is angled at 90 degrees with respect to a central axis of the second chamber and is directed toward a midpoint between the plurality of ports on the exhaust valve side . 4. The internal combustion engine according to claim 1, wherein the internal combustion engine is a gasoline engine using gasoline as fuel.

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