Internal combustion engine with sub-combustion chamber

Abstract

In an internal combustion engine equipped with a sub-combustion chamber that enables lean burn, a structure is disclosed that allows for easy detection of blockage in the flame ejection hole of the sub-combustion chamber and also facilitates measures to restore the blockage. [Solution] A pressure sensor 25 capable of detecting pressure fluctuations in the main combustion chamber is provided in the cylinder head 3. When some of the flame ejection holes 22 in the sub-combustion chamber 15 become clogged, the size of the jet flame 23 ejected from the flame ejection holes 22 changes, causing the combustion pressure in the main combustion chamber to become uneven. This results in unevenness in the waveform of the pressure fluctuations during the expansion stroke, and it is also predicted that a unique pressure wave will be generated. The pressure sensor 25 detects the unevenness of the waveform and the unique pressure wave to detect clogging of the flame ejection holes 22. Subsequently, the internal air-fuel ratio of the sub-combustion chamber 15 is changed to the stoichiometric ratio to burn off deposits with a jet flame.

Description

Technical Field

[0001] The present invention relates to an internal combustion engine with a sub-combustion chamber.

Background Art

[0002] In internal combustion engines such as gasoline engines and gas engines, it has been proposed to provide a sub-combustion chamber (sub-chamber) in the cylinder head. The sub-combustion chamber is used in combination with a spark plug, and the flame generated in the sub-combustion chamber is ejected from the flame ejection hole into the main combustion chamber to ignite the main fuel. Since the flame generated in the sub-combustion chamber is atomized and has excellent ignition properties of the fuel, there is an advantage that combustion can be surely performed even when the air-fuel ratio is slightly lean. Therefore, it has been attracting attention as a promising technology for improving fuel efficiency and promoting exhaust gas purification.

[0003] As means for igniting the air-fuel mixture in the sub-combustion chamber, there are a passive method in which the air-fuel mixture ejected from the intake port is taken into the sub-combustion chamber and ignited by a spark plug exposed inside the sub-combustion chamber, and an active method in which sub-fuel is taken into the sub-combustion chamber from a dedicated injector and the sub-fuel is ignited by a spark plug. However, in either case, it is assumed that deposits such as carbon adhere during long-term operation and clogging occurs in the flame ejection hole.

[0004] The clogging of the flame ejection hole is assumed to be a case where a part of the plurality of flame ejection holes is clogged and a case where all of the plurality of flame ejection holes are clogged. In any case, when clogging occurs in the flame ejection hole, the ejection of the jet flame becomes incomplete, resulting in combustion instability.

[0005] Therefore, it has been proposed to detect blockages in the flame ejection holes and, if a blockage is detected, to take recovery measures to remove the deposits. As an example, Patent Document 1 describes an active type sub-combustion chamber in which blockages are detected from changes in the combustion pressure of the sub-combustion chamber, and if it is determined that the flame ejection holes are blocked, the supply of sub-fuel to the sub-chamber is stopped, and main fuel is taken from the main combustion chamber into the sub-combustion chamber, where the main fuel is ignited inside the sub-combustion chamber to generate a flame.

[0006] To further describe the recovery measures in Patent Document 1, it is based on the understanding that when auxiliary fuel is supplied to the auxiliary combustion chamber, the casing constituting the auxiliary combustion chamber is cooled by the cooling effect of the auxiliary fuel, making it difficult to remove deposits. Therefore, by stopping the supply of auxiliary fuel, the casing is kept at a high temperature, and the deposits are burned off by the jet flame. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-133464 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Detecting blockages in the flame ejection holes and eliminating deposits are crucial issues for improving the reliability of internal combustion engines with sub-combustion chambers that enable lean burn and high EGR. However, Patent Document 1 requires pressure sensors in both the sub-combustion chamber and the main combustion chamber as means of detecting blockages in the flame ejection holes, which complicates the structure and increases costs. In particular, providing a pressure sensor in the sub-combustion chamber presents a significant hurdle to implementation due to space constraints.

[0009] Furthermore, while Patent Document 1 detects clogging of the flame ejection hole from the change in pressure in the main combustion chamber when the combustion timing in the sub-combustion chamber is shifted, shifting the combustion timing in the sub-combustion chamber is equivalent to advancing or retarding the ignition timing, so there are concerns that it may interfere with the control of steady-state operation.

[0010] Furthermore, while Patent Document 1 employs a passive approach as a means of eliminating deposits, there remains concern as to whether simply burning lean fuel from the main combustion chamber in the sub-combustion chamber is sufficient to burn off the deposits. Moreover, Patent Document 1 is only applicable to active systems, which is problematic as it lacks versatility.

[0011] The present invention was made against this backdrop, and aims to achieve detection of blockage in the flame outlet and removal of deposits with a simple structure. [Means for solving the problem]

[0012] The present invention is, "It has a main combustion chamber that drives the piston, and a sub-combustion chamber that communicates with the main combustion chamber via a plurality of flame ejection holes, and is set to operate steadily at an air-fuel ratio lower than the stoichiometric air-fuel ratio." In an internal combustion engine, "The system includes an in-cylinder state detection means for detecting the pressure or vibration of the main combustion chamber, and a control device capable of adjusting the air-fuel ratio of at least the sub-combustion chamber based on the value detected by the in-cylinder state detection means." When the in-cylinder state detection means detects pressure fluctuations or abnormal vibrations that are presumed to be caused by uneven combustion resulting from a blockage in the flame ejection hole, the system controls the air-fuel ratio in the sub-combustion chamber to be at least as high as or higher than the stoichiometric air-fuel ratio. It has the following characteristics.

[0013] The present invention is applicable to both active and passive combustion systems. In the passive system, if the air-fuel ratio of the sub-combustion chamber is set to the stoichiometric air-fuel ratio or higher, the air-fuel ratio of the main combustion chamber will be controlled. In the active system, the air-fuel ratio of the sub-combustion chamber may be adjusted while the main combustion chamber remains lean, or the main combustion chamber may also be set to the stoichiometric air-fuel ratio.

[0014] As a means for detecting the in-cylinder state, for example, a pressure sensor that detects combustion pressure can be used. A piezoelectric element type is considered preferable for the pressure sensor in terms of heat resistance and reliability.

[0015] Specifically, as a means of detecting blockage in the flame outlet holes, the vibration or waveform during steady-state operation when no blockage occurs is stored in a map as a reference state, while the system is operated with the flame outlet holes blocked in advance, and the resulting fluctuation in combustion pressure is set as an abnormal state. When the actual vibration frequency or waveform detected by the in-cylinder state detection means shifts from the reference state to an abnormal state, and that abnormal state continues for a predetermined time or cycle, it can be determined that blockage in the flame outlet holes has occurred.

[0016] Since there are generally 3 to 10 flame outlets in the sub-combustion chamber, by setting multiple clogging patterns and acquiring operating data in advance, the relationship between clogging patterns and abnormal conditions such as pressure fluctuations can be created as multiple maps. By detecting how the abnormal pattern has shifted from the reference map during normal operation, the state of clogging in the flame outlets can be accurately detected. If signs of clogging in the flame outlets are observed, it is preferable to promptly implement purification treatment control.

[0017] Furthermore, pressure fluctuations within the cylinder are not only affected by clogged flame vents, but also by changes in the air-fuel ratio due to the introduction of EGR gas, changes in the air-fuel ratio due to the recirculation of blow-by gas, and changes in the air-fuel ratio due to the introduction of purge gas. In the case of internal combustion engines for automobiles, the effects of changes in driving conditions should also be considered. Therefore, it is necessary to eliminate (correct for) the effects of pressure fluctuations caused by other factors and to extract pressure fluctuations and abnormal vibrations caused by clogged flame vents. [Effects of the Invention]

[0018] If multiple flame outlets are not clogged and a normal jet flame is ejected evenly from each outlet, the combustion pressure is expected to change evenly in each part of the main combustion chamber. Therefore, even if pressure fluctuations change with rotational speed, the change in combustion pressure in the main combustion chamber is expected to appear as a smooth waveform (standing wave) with a constant amplitude repeating. This point is assumed to remain unchanged even with the inflow of EGR gas, blow-by gas, or purge gas.

[0019] On the other hand, if deposits adhere to some of the flame outlets, differences in the passage area of ​​each flame outlet will occur, resulting in uneven ejection of the jet flame from each outlet. Consequently, variations in the combustion state in the main combustion chamber are expected to occur, such as the intake side having a higher pressure than the exhaust side, causing the pressure in the main combustion chamber to vary depending on the location. Then, it is expected that these pressure variations in the main combustion chamber will manifest as changes in the vibration waveform, or as small, characteristic vibrations such as shock waves.

[0020] In other words, when a unique pressure fluctuation occurs in the main combustion chamber due to a blockage of the flame ejection holes, it is expected that this pressure fluctuation will produce a unique waveform or a unique small vibration. By detecting this unique waveform change or the occurrence of unique vibrations using the in-cylinder state detection means, the blockage of the flame ejection holes can be detected. Furthermore, since this detection can be performed at any time under normal operation, it does not interfere with the control of the operation.

[0021] Furthermore, in the invention of the present application, as a deposit removal means for the flame ejection holes, since the fuel pressure inside the sub-combustion chamber is increased to burn off the deposits with jet flames, the removal of deposits can be ensured, and either an active type or a passive type can be applied, showing excellent versatility.

Brief Description of the Drawings

[0022] [Figure 1] It is a longitudinal side view showing the intake port and the exhaust port. [Figure 2] It is a longitudinal side view of the central part. [Figure 3] (A) is a longitudinal side view of the sub-combustion chamber, (B) is a plan cross-sectional view showing a normal flame ejection state, and (C) is a plan cross-sectional view showing a flame ejection state in an example where clogging has occurred in the flame ejection holes. [Figure 4] It is a longitudinal side view schematically showing the main combustion chamber in an example where clogging has occurred in some of the flame ejection holes. [Figure 5] It is a schematic block diagram of the control device. [Figure 6] It is a graph showing the pressure fluctuation in the main combustion chamber. (A) shows the pressure fluctuation in a normal main combustion chamber, and (B) shows the pressure fluctuation in an abnormal main combustion chamber. [Figure 7] It is a flowchart of a control example.

Embodiments for Carrying Out the Invention

[0023] (1). Basic Structure Next, embodiments of the invention of the present application will be described based on the drawings. Hereinafter, the words "front and rear" and "left and right" are used to specify directions. The front-rear direction is the crankshaft axis direction, and the left-right direction is the direction orthogonal to the crankshaft axis direction and the cylinder bore axis direction. Regarding the front and the rear, the side where the timing chain is arranged is regarded as the front, and the side where the transmission is arranged is regarded as the rear. <0000​​This embodiment is applied to an internal combustion engine for automobiles. As shown in Figures 1 to 3, the internal combustion engine has a cylinder block 1 as its basic element and a cylinder head 3 fixed to its upper surface via a gasket 2. The cylinder block 1 has a plurality of cylinder bores 4 arranged in the direction of the crank axis, and a piston 5 is slidably fitted into each cylinder bore 4.

[0025] On the other hand, the cylinder head 3 has a pent-roof-shaped downward recess 6 facing the cylinder bore 4, and the main combustion chamber is formed by the cylinder bore 4 of the cylinder block 1 and the recess 6 of the cylinder head 3.

[0026] The cylinder head 3 has a pair of intake ports 7 and a pair of exhaust ports 8, arranged on both the left and right sides of the crank axis, corresponding to each recess 6. The intake outlet hole 7a of the intake port 7 is opened and closed by the intake valve 9, and the exhaust inlet hole 8a of the exhaust port 8 is opened and closed by the exhaust valve 10. Each valve 9 and 10 is biased in the closing direction by a spring 11. Valve seats are fitted into the intake outlet hole 7a and the exhaust inlet hole 8a.

[0027] Each of the pair of intake ports 7 is independent along its entire length and opens onto the intake side 3a of the cylinder head 3. An intake manifold 12 is fixed to the intake side 3a of the cylinder head 3. Fuel injection injectors 13 are mounted on the intake manifold 12, corresponding to each intake port 7. The fuel injection injectors 13 can also be mounted on the cylinder head 3.

[0028] In the cylinder head 3, a spark plug hole 14 is opened in the portion of the top surface of each recess 6 enclosed by the intake outlet hole 7a and the exhaust inlet hole 8a, and a spark plug 16 equipped with a sub-combustion chamber 15 is screwed into the spark plug hole 14. The axis of the spark plug hole 14 is offset slightly toward the exhaust side from the axis of the cylinder bore 4, but it may also be positioned concentrically with the cylinder bore 4. In Figures 1 to 3, reference numeral 17 indicates a water jacket through which cooling water flows.

[0029] (2) Spark plugs and fuel injectors As clearly shown in Figure 3, the sub-combustion chamber 15 is formed in a cylindrical shape with a dome portion exposed in a downward recess 6. On the other hand, the spark plug 16 has a metal body 18 with male threads formed on its outer circumference. In this embodiment, the sub-combustion chamber 15 is made of an insulator and is fixed to the body 18 of the spark plug 16 by welding.

[0030] If the sub-combustion chamber 15 is a separate structure from the spark plug 16, it is possible to weld the sub-combustion chamber 15 to the cylinder head 3 or screw it in from below to fix it to the cylinder head 3. In addition, although the sub-combustion chamber in this embodiment is a passive type that takes in the air-fuel mixture from the main combustion chamber, an active type equipped with a dedicated sub-injector can also be adopted.

[0031] The spark plug 16 comprises a central electrode 19 protruding downward at the axial position of the main body 18 and a ground electrode 20 protruding downward from a portion closer to the outer circumference of the main body 18, and both are electrically insulated from the main body 18 and the sub-combustion chamber. The ground electrode 20 is inclined to become lower towards the tip (away from the main body 18), but it can also be formed in an L-shape having a portion parallel to the axis O of the main body 18 and a portion perpendicular to it.

[0032] On the other hand, at the dome portion at the lower end of the sub-combustion chamber 15, a group of flame ejection holes 22 are arranged circumferentially, opening in a direction intersecting the axis. Although eight flame ejection holes 22 are shown in the figure, the number can be set arbitrarily. They can also be formed at different heights, and some facing directly downwards can be added.

[0033] Fuel is injected from the fuel injection injector 13 and spreads out in a tapered shape. The center line of the injection direction (center line of the injection spread) is set to generally pass through the center of the intake outlet hole 7a of the intake port 7 when viewed in a longitudinal front view from the direction of the crank axis. The operating timing of the fuel injection injector 13 and the opening and closing timing of the intake valve 9 can be either a system in which fuel injection by the fuel injection injector 13 begins after the intake valve 9 opens, or a system in which fuel injection begins when the valve is closed.

[0034] (3) Basic configuration of measures for detecting and recovering blockages in flame outlet holes When current is supplied to the spark plug 16, fuel burns inside the sub-combustion chamber, and as shown in Figure 3, the combustion gas becomes a jet flame 23 and is ejected from each flame ejection hole 22. The internal combustion engine of this embodiment is set to operate steadily in a lean-burn system in which a mixture with an air-fuel ratio lower than the stoichiometric ratio is supplied to the main combustion chamber. However, because the jet flame 23 is fast and has excellent ignition properties, even in a lean-burn system where the air-fuel ratio of the mixture is leaner than the stoichiometric ratio, the main fuel can be reliably ignited and the engine can operate.

[0035] However, over time, as shown in Figure 3(C), deposits 24 may accumulate in some of the flame ejection holes 22, causing blockages and reducing the passage area of ​​the flame ejection holes 22. Consequently, the jet flames 23 ejected from the blocked flame ejection holes 22 will be thinner, while the jet flames 23 ejected from the other unblocked flame ejection holes 22 will be thicker than normal. This is expected to result in uneven combustion conditions in the main combustion chamber.

[0036] Therefore, it is necessary to provide a detection means to detect blockage in the flame outlet hole 22 and, if blockage is detected, to perform a purification process to remove the deposit 24. In this embodiment, as shown in Figure 2, a pressure sensor 25 is placed in the intake side portion of the cylinder head 3, with its tip exposed on the inner surface of a recess 6, as a blockage detection means.

[0037] The pressure sensor 25 is positioned between a pair of intake ports 7, and its mounting hole 26 opens onto the intake side of the cylinder head 3. While the pressure sensor 25 can also be positioned on the exhaust side, it is preferable to position it on the intake side to suppress heat damage. In this embodiment, the center line of the pressure sensor 25 is inclined with respect to the inner surface of the recess 6 when viewed from the crank axis direction, but it is also possible to position the pressure sensor 25 perpendicular to the inner surface of the recess 6 (in this case, the cable 25a of the pressure sensor 25 will be routed from inside the cylinder head 3).

[0038] In this embodiment, as a recovery measure in the event of clogging of the flame ejection hole 22, the fuel injection injector 13 is controlled so that the air-fuel ratio of the mixture supplied to the main combustion chamber becomes the stoichiometric air-fuel ratio. This increases the amount of combustion in the sub-combustion chamber, raising the combustion pressure and combustion temperature, which allows the deposit 24 to be burned off by the jet flame 23.

[0039] The detection and recovery of blockages in the flame vent holes 22 are performed by a control device 27, which is incorporated into the ECU (Engine Control Unit). The control device 27 uses a central processing unit (CPU) as its core device, and is connected to the CPU as sensors, including a pressure sensor 25, a throttle sensor that detects the opening degree of the throttle valve, a rotation sensor that detects the rotation speed of the crankshaft, an intake pressure sensor installed in the surge tank, a water temperature sensor that detects the coolant temperature, and O2 sensors and AF sensors installed in the exhaust system.

[0040] It also has ROM and RAM as memory, and the drivetrain elements connected to it include a throttle valve, fuel injection injector 13, EGR valve, spark plug 16, and VVT (variable valve timing device).

[0041] (4) Details of measures to detect and recover blockages in flame vents Now, the pressure in the main combustion chamber fluctuates with the reciprocating motion of the piston 5 (rotation of the crankshaft). Roughly speaking, as shown in Figure 6, the pressure immediately after ignition is the highest pressure and the pressure at bottom dead center during the intake stroke is the lowest pressure, resulting in a cycle in a four-stroke internal combustion engine that generates a pressure fluctuation wave with a period of 720 degrees.

[0042] Because pressure fluctuates complexly during the exhaust, intake, and compression processes, the actual waveform does not appear as a clean sinusoidal wave as shown in Figure 6(A). However, if there is no blockage in the flame outlets 22 of the sub-combustion chamber 15, the fuel burns uniformly in the main combustion chamber, and the pressure fluctuation appears as a smooth standing wave 28, as schematically shown in Figure 6(A). Therefore, by passing the detected value of the pressure sensor 25 through a bandpass filter (BPF), the smooth standing wave 28 during normal operation can be detected, and the normal state can be recognized.

[0043] On the other hand, if some of the flame ejection holes 22 in the sub-combustion chamber 15 become clogged, the combustion inside the main combustion chamber becomes uneven, as described above. That is, as shown by the dense dots in Figure 4, the combustion rate is faster and the pressure is higher in areas exposed to a thick jet flame 23, and as shown by the sparse dots in Figure 4, the combustion rate is slower and the pressure is lower in areas exposed to a thin jet flame 23. As a result, the pressure inside the main combustion chamber becomes uneven. However, since the pressure differences influence each other in the main combustion chamber, the pressure fluctuations do not form a smooth curve, but rather appear as abnormal waves that decrease the pressure while changing amplitude in small increments, as shown by the reference numeral 29 in Figure 6(B).

[0044] Therefore, by calculating the rate of change (derivative value) of the pressure fluctuation waveform during the expansion process after passing through the bandpass filter (BPF), if the pressure does not decrease smoothly but shows uneven fluctuations, it is provisionally determined that an abnormal wave 29 is being generated due to clogging of the flame ejection hole 22. If this condition continues for a predetermined time (e.g., several seconds to tens of seconds) or a predetermined cycle, it can be definitively determined that an abnormal wave 29 is occurring due to clogging of the flame ejection hole 22, as shown in the flow chart of Figure 7.

[0045] If it is determined that the cause of the pressure fluctuation is due to clogging of the flame outlet hole 22, the mixture in the main combustion chamber is switched to the stoichiometric air-fuel ratio and the system is operated as shown in Figure 7. After a predetermined time (e.g., several seconds to several minutes) or a predetermined cycle has elapsed, the pressure change in the expansion process is detected again to determine whether the abnormal value persists. If the abnormal value is resolved, the system is returned to the lean burn state; if the abnormal value persists, combustion at the stoichiometric air-fuel ratio is continued, and this process is repeated.

[0046] The pressure in the main combustion chamber changes in conjunction with the movement of the piston and the valve. However, if a blockage occurs in the flame ejection hole 22, a small-amplitude pressure wave is generated during the expansion process. This wave reflects within the main combustion chamber, and it is expected that a fine wave with repeated small vibrations will be generated with each expansion process, as shown by the reference numeral 30 in Figure 6(B). In other words, if a blockage occurs in the flame ejection hole 22, it is expected that a phenomenon will occur in which the combustion gas vibrates during the expansion process.

[0047] Therefore, it is understood that blockage of the flame outlet 22 can also be detected by detecting the micro-waves 30 that vibrate with each expansion process. It is understood that the accuracy can be further improved by determining blockage of the flame outlet 22 by simultaneously detecting the abnormal waves 29 caused by pressure changes due to piston movement and the micro-waves 30 caused by vibrations of the combustion gas itself. Since the frequency of the micro-waves 30 is predicted to be 6 to 20 kHz, it is preferable to set the system to detect waves in this vibration range with a bandpass filter, as this simplifies the structure.

[0048] Since clogging of the flame outlet 22 does not occur frequently, detection once a day, for example, may be sufficient. It is also possible to link it with the odometer and increase the detection frequency (shorten the detection interval) as the mileage increases.

[0049] Furthermore, it is understood that the flame outlet 22 is more likely to become clogged when the EGR gas return flow rate is high, and that there are operating ranges that are more likely to induce clogging of the flame outlet 22, such as when it is unavoidable to operate in a rich state at or above the stoichiometric air-fuel ratio due to the need for high-load operation such as driving uphill. Therefore, it is possible to adopt a control system that stores such operating conditions as data in memory and increases the detection frequency if the operation that is likely to induce clogging of the flame outlet 22 continues.

[0050] These control systems can be integrated into each vehicle's ECU for independent control, or they can transmit data to a central location via a wireless internet connection, allowing for monitoring and remote control if an anomaly is detected. Upgraded control programs can also be provided to each vehicle's ECU via the internet.

[0051] Although embodiments of the present invention have been described above, the present invention can be implemented in various other ways. For example, a vibration meter can be used as the means for detecting the state inside the cylinder. [Industrial applicability]

[0052] The present invention can be implemented in an internal combustion engine with a sub-combustion chamber to promote lean burn. Therefore, it is industrially applicable. [Explanation of symbols]

[0053] 1 Cylinder Block 3 Cylinder head 4 Cylinder Bore 5 pistons 6 Recesses that make up the main combustion chamber 7 Intake port 8 exhaust ports 13 Fuel Injector 14 plug holes 15. Sub-combustion chamber 16 Spark plugs 18 Main unit 19 Center electrode 20 Ground electrode 22 Flame spout hole 23 Jet flames 24. Deposits causing blockages 25 Pressure sensor as an example of a means for detecting the state inside a cylinder 27 Control device 28. Standing waves under normal conditions 29 Abnormal wave 30 Microwaves

Claims

[Claim 1] An internal combustion engine having a main combustion chamber for driving a piston and a sub-combustion chamber connected to the main combustion chamber via a plurality of flame ejection holes, and configured to operate steadily at an air-fuel ratio lower than the stoichiometric air-fuel ratio, The system includes an in-cylinder state detection means for detecting the pressure or vibration of the main combustion chamber, and a control device capable of adjusting the air-fuel ratio of at least the sub-combustion chamber based on the value detected by the in-cylinder state detection means. When the in-cylinder state detection means detects pressure fluctuations or abnormal vibrations that are presumed to be caused by uneven combustion resulting from a blockage in the flame ejection hole, the air-fuel ratio in the sub-combustion chamber is controlled to be at least as high as or higher than the stoichiometric air-fuel ratio. An internal combustion engine with a secondary combustion chamber.

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