Engine system and internal combustion engine control method

Abstract

An engine system (S) includes an internal combustion engine (1) and a control unit (100). The internal combustion engine includes: a main chamber (5) defined by a piston (2), a cylinder (3), and a cylinder head (4); a spark plug (10) mounted on the cylinder head; a secondary chamber tube (11) surrounding the spark plug and protruding downward from the cylinder head; a secondary chamber hole (17) formed in the piston and capable of receiving the secondary chamber tube; and an injector (9) for injecting fuel supplied into the main chamber. The control unit ignites the spark plug when the secondary chamber tube is inserted into the secondary chamber hole, and injects fuel from the injector before the spark plug is ignited and before the secondary chamber tube is inserted into the secondary chamber hole.

Description

Technical Field

[0001] The present disclosure relates to an engine system including an internal combustion engine and a control unit, and a method for controlling the internal combustion engine. Background Art

[0002] Generally, in a spark-ignition internal combustion engine, ignition is initiated before compression top dead center (CTDC), and peak in-cylinder pressure is achieved after compression top dead center. Furthermore, by advancing the ignition timing, peak in-cylinder pressure is increased, thereby increasing the engine's output torque.

[0003] Furthermore, a spark ignition type internal combustion engine having an auxiliary combustion chamber in addition to a normal combustion chamber formed in a cylinder is known (for example, see Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-285273 Summary of the Invention

[0007] Technical problem to be solved by the invention

[0008] In typical spark-ignition internal combustion engines, peak in-cylinder pressure occurs after compression top dead center (CTDC). Consequently, this peak occurs at a time when the mechanical efficiency of converting in-cylinder pressure to crankshaft torque is not necessarily optimal. Therefore, even if ignition timing is advanced to increase the peak in-cylinder pressure, the torque converted to the crankshaft is not significant enough, making it difficult to improve the thermal efficiency of the internal combustion engine.

[0009] Therefore, the present disclosure has been made in view of the above circumstances, and an object thereof is to provide an engine system and a control method of an internal combustion engine that are advantageous in improving the thermal efficiency of an internal combustion engine.

[0010] Technical means for solving technical problems

[0011] According to one embodiment of the present disclosure, an engine system is provided.

[0012] The engine system includes an internal combustion engine and a control unit. The internal combustion engine includes:

[0013] a main chamber defined by the piston, cylinder, and cylinder head;

[0014] a spark plug mounted on the cylinder head;

[0015] a secondary chamber pipe surrounding the spark plug and protruding downward from the cylinder head;

[0016] a sub-chamber hole formed in the piston and capable of receiving the sub-chamber tube; and

[0017] an injector that injects the fuel supplied into the main chamber,

[0018] The control unit is configured to control the ignition timing of the spark plug and the injection amount and injection timing of the injector.

[0019] When the auxiliary chamber tube is inserted into the auxiliary chamber hole, the spark plug is ignited.

[0020] Fuel is injected from the injector before the spark plug is ignited and before the sub-chamber tube is inserted into the sub-chamber hole.

[0021] Preferably, the control unit controls the ignition timing so that a peak in-cylinder pressure generated after ignition of the spark plug occurs at a timing at which an angle formed by a crankshaft radius and a connecting rod center axis is 90° or approximately 90°.

[0022] Preferably, the timing at which the peak of the in-cylinder pressure occurs is a timing within a range of 10 to 80 degrees after compression top dead center.

[0023] Preferably, the sub-chamber tube has a certain outer diameter, and the sub-chamber hole has a certain inner diameter that is larger than the outer diameter of the sub-chamber tube.

[0024] According to another embodiment of the present disclosure, a method for controlling an internal combustion engine is provided.

[0025] The internal combustion engine comprises:

[0026] a main chamber defined by the piston, cylinder, and cylinder head;

[0027] a spark plug mounted on the cylinder head;

[0028] a secondary chamber pipe surrounding the spark plug and protruding downward from the cylinder head;

[0029] a sub-chamber hole formed in the piston and capable of receiving the sub-chamber tube; and

[0030] an injector that injects the fuel supplied into the main chamber,

[0031] The control method of the internal combustion engine comprises:

[0032] a first step of causing the injector to inject fuel before the spark plug is ignited and before the sub-chamber tube is inserted into the sub-chamber hole; and

[0033] The second step is to ignite the spark plug when the sub-chamber tube is inserted into the sub-chamber hole.

[0034] Effects of the Invention

[0035] According to the present disclosure, it is possible to provide an engine system and a method for controlling an internal combustion engine that are advantageous in improving the thermal efficiency of an internal combustion engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic longitudinal sectional view showing the engine system.

[0037] Figure 2 It is a schematic longitudinal sectional view showing the vicinity of the spark plug at the timing of compression top dead center.

[0038] Figure 3 This is a graph showing the relationship between the crank angle and the cylinder pressure.

[0039] Figure 4 It is a schematic diagram showing the state of the timing of occurrence of the peak of the in-cylinder pressure in a comparative example.

[0040] Figure 5 It is a schematic longitudinal sectional view showing the vicinity of the spark plug at a timing after compression top dead center.

[0041] Figure 6 Yes Figure 5 A schematic longitudinal sectional view of the vicinity of the spark plug at a timing subsequent to the timing of .

[0042] Figure 7 This is a schematic diagram showing the state of the timing at which the peak of the in-cylinder pressure occurs in this embodiment.

[0043] Figure 8 It is a schematic diagram showing the state of the compression stroke in a comparative example.

[0044] Figure 9 This is a schematic diagram showing the state of the compression stroke in the first example of the present embodiment.

[0045] Figure 10 This is a schematic diagram showing the state of the compression stroke in the second example of the present embodiment. DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Note that the present disclosure is not limited to the following embodiments.

[0047] like Figure 1As shown, the engine system S of this embodiment includes an internal combustion engine 1 and an electronic control unit (ECU) 100, which serves as a control unit, circuit element, or controller for controlling the internal combustion engine 1. As is well known, the ECU 100 includes a CPU (Central Processing Unit) with computing capabilities, ROM (Read Only Memory) and RAM (Random Access Memory) as storage media, input / output ports, and storage devices other than the ROM and RAM.

[0048] Engine 1 is a spark-ignition internal combustion engine, specifically, a gas engine that uses compressed natural gas (CNG (Compressed Natural Gas)) as fuel. However, it can also be a gasoline engine that uses gasoline as fuel, or it can be a spark-ignition internal combustion engine that uses other fuels. The engine 1 of this embodiment is for vehicles, and is particularly used as a power source for large vehicles such as trucks. However, the use of the engine is not limited to this, and it can also be an engine for mobile bodies other than vehicles, such as ships, construction machinery, or industrial machinery. In addition, the engine may not be an engine mounted on a mobile body, but may also be a fixed engine. In Figure 1 Although only one cylinder is shown in FIG, the engine 1 of this embodiment is a multi-cylinder engine. The engine 1 includes a turbocharger (not shown).

[0049] Engine 1 includes a piston 2; a cylinder 3 that coaxially accommodates piston 2 and can be raised and lowered; a cylinder head 4 that closes the upper opening of cylinder 3; and a main chamber 5, which serves as the main combustion chamber defined by piston 2, cylinder 3, and cylinder head 4. Main chamber 5 corresponds to the combustion chamber of a typical spark-ignition internal combustion engine.

[0050] The cylinder head 4 is formed with an intake port 7 and an exhaust port 8. These intake port 7 and exhaust port 8 are opened and closed by an intake valve and an exhaust valve, respectively, not shown. An injector 9 is provided in the intake port 7. Injector 9 injects fuel F, which will then be supplied to the main chamber 5, into the intake port 7. Therefore, injector 9 constitutes a port injection injector.

[0051] The injector may be a direct injection injector that directly injects fuel into the cylinder 3 or a combination of a port injection injector and a direct injection injector. Any type of injector may be used as long as it can inject the fuel F supplied into the main chamber 5.

[0052] The cylinder axis, which is the center axis of the cylinder, is denoted by reference symbol C. Hereinafter, unless otherwise specified, the axial direction, radial direction, and circumferential direction based on the cylinder axis C are simply referred to as the axial direction, radial direction, and circumferential direction.

[0053] A spark plug 10 and a secondary chamber tube 11 surrounding the spark plug 10 are mounted at the radial center of the cylinder head 4. The spark plug 10 and secondary chamber tube 11 are coaxially arranged with the cylinder axis C and protrude downward from the cylinder head 4. As is well known, the spark plug 10 includes a center electrode 13, an outer electrode 14, and an insulator 15 interposed between these electrodes.

[0054] The secondary chamber tube 11 is cylindrical and extends axially, surrounding the spark plug 10 with a radial gap. The secondary chamber tube 11 protrudes from the cylinder head 4 to a greater extent than the spark plug 10. The secondary chamber tube 11 is a straight tube with a constant inner diameter d1 and outer diameter D1. The lower end surface 12 of the secondary chamber tube 11 is perpendicular to the axial direction. The lower end of the secondary chamber tube 11 opens into the main chamber 5.

[0055] Meanwhile, a sub-chamber hole 17 is formed on the upper surface 6 of the piston 2, into which the sub-chamber tube 11 can be inserted. Sub-chamber hole 17 is a bottomed cylindrical shape extending axially, with an open upper end and a closed lower end. Sub-chamber hole 17 has a constant inner diameter d2. This inner diameter d2 is slightly larger than the outer diameter D1 of the sub-chamber tube 11. The lower end surface, or bottom surface 18, of sub-chamber hole 17 is perpendicular to the axial direction.

[0056] Figure 2 The figure shows the state at compression top dead center (TDC). In this state, the auxiliary chamber tube 11 is inserted into the auxiliary chamber hole 17, and the two together form the auxiliary combustion chamber, or auxiliary chamber 16. The auxiliary chamber 16, also known as the front chamber, is a combustion chamber with a smaller volume than the main chamber 5. Figure 2 The figure shows the state in which the auxiliary chamber tube 11 is fully inserted into the auxiliary chamber hole 17 and the volume of the auxiliary chamber 16 is minimized. When the auxiliary chamber tube 11 is inserted, an axial gap (referred to as a bottom gap) 19 is formed between the lower end surface 12 of the auxiliary chamber tube 11 and the bottom surface 18 of the auxiliary chamber hole 17. A radial gap (referred to as a circumferential gap) 22 is formed between the outer peripheral surface 20 of the auxiliary chamber tube 11 and the inner peripheral surface 21 of the auxiliary chamber hole 17.

[0057] return Figure 1 A piston pin hole 23 is provided below the auxiliary chamber hole 17 in the piston 2. As is well known, a piston pin (not shown) is inserted into the piston pin hole 23, and the piston 2 is connected to the small end of the connecting rod (not shown) via the piston pin.

[0058] The ECU 100 is configured to control the ignition timing of the spark plug 10 and the injection amount and injection timing of the injector 9. These control methods will be described below.

[0059] First, a conventional spark-ignition internal combustion engine (referred to as a comparative example) differing from the present embodiment will be described. In this comparative example, a sub-chamber is not provided, and the spark plug is positioned centrally within the main chamber. Furthermore, when the spark plug is ignited, the fuel-air mixture within the main chamber burns radially outward from the ignition point. The comparative example also includes a port-injection injector, whose injection timing is during or before the intake stroke.

[0060] Figure 3 The relationship between crank angle θ and in-cylinder pressure P is shown. The in-cylinder pressure here refers to the pressure within the main chamber. Lines a, b, and c represent the comparative example. Ignition timing advances as the timing follows lines a, b, and c. For example, line a indicates ignition timing 10° before compression top dead center (BTDC), line b indicates 15° before compression top dead center (BTDC), and line c indicates 20° before compression top dead center (BTDC).

[0061] In the figure, Plim represents the maximum value of the cylinder pressure at which knocking does not occur, i.e., the knock limit, in the comparative example and the present embodiment. Furthermore, the compression ratio of the engine of the comparative example is a predetermined general value (e.g., 10.0), which is referred to as the base compression ratio.

[0062] As shown in the figure, in the comparative example, the maximum in-cylinder pressure peak (expressed as pa, pb, and pc) occurs after compression top dead center (e.g., around 15° ATDC). Furthermore, as the ignition timing is advanced, the in-cylinder pressure value (in-cylinder peak pressure) of the in-cylinder pressure peak increases, gradually approaching the knock limit Plim, and the timing of the in-cylinder pressure peak also gradually advances.

[0063] However, the timing after the compression top dead center, where such a peak in-cylinder pressure occurs, is a timing at which the mechanical efficiency of converting the in-cylinder pressure into the torque of the crankshaft is not necessarily good.

[0064] Figure 4Indicates the positions of the piston 2, connecting rod 25, and crankshaft 26 at the timing of the peak in-cylinder pressure. The in-cylinder pressure P generates a downward force on the piston 2, which is transmitted to the crankshaft 26 through the connecting rod 25 and converted into a torque for rotating the crankshaft 26. However, at this timing, the angle θ formed by the crankshaft radius R connecting the center of the crankshaft and the center of the crankpin and the connecting rod center axis Cc is much larger than 90° and is approximately 180°. Therefore, the length r of the force arm when calculating the torque of the force applied to the crankshaft 26 is much shorter than the crankshaft radius R. Even if a large in-cylinder pressure P is applied, not much torque is applied to the crankshaft 26. Therefore, the mechanical efficiency when converting the in-cylinder pressure into the torque of the crankshaft (hereinafter referred to as mechanical efficiency) is not necessarily good.

[0065] like Figure 3 As shown, even though the peak in-cylinder pressure increases by advancing the ignition timing, the timing of the peak in-cylinder pressure does not change much. Instead, it gradually advances, increasing the angle θ and shortening the length r of the moment arm. Consequently, the rate of increase in torque relative to the amount of advancement is not significant. Even with advancing the ignition timing, the torque does not increase significantly, making it difficult to improve the engine's thermal efficiency.

[0066] Therefore, in order to solve this technical problem, in this embodiment, the engine having the above-described configuration is used to perform the following control.

[0067] exist Figure 3 In the figure, line d represents the situation of this embodiment. The ignition timing in this embodiment is the time when the sub-chamber tube 11 is inserted into the sub-chamber hole 17, forming the sub-chamber 16. Specifically, it is near compression top dead center, preferably at or after compression top dead center, but it can also be before compression top dead center. In either case, it is preferably later than the comparative example.

[0068] exist Figure 3 As an example, the ignition timing θig of this embodiment, which is equal to compression top dead center (TDC), is shown. Before this ignition timing θig, the in-cylinder air-fuel mixture does not self-ignite. Therefore, before ignition timing θig, the in-cylinder pressure rises, similar to when the engine is motored. If ignition is performed at ignition timing θig, the in-cylinder air-fuel mixture ignites and burns, and the in-cylinder pressure gradually rises.

[0069] like Figure 2 As indicated by the asterisk, if ignition occurs at compression top dead center, the mixture in the sub-chamber 16 ignites and burns (this is called sub-combustion). The resulting flame or flame kernel spreads radially from the entire circumference into the main chamber 5 through the bottom gap 19 and the peripheral gap 22, propagating into the main chamber 5 and combusting the mixture in the main chamber 5.

[0070] After ignition, piston 2 Figure 5As shown, the flame in the auxiliary chamber 16 gradually descends, and at the same time, as shown by arrow a, the flame in the auxiliary chamber 16 propagates into the main chamber 5 through the bottom gap 19 and the peripheral gap 22. As the piston 2 descends, the bottom gap 19 gradually increases, and the size of the peripheral gap 22 remains approximately constant. The flame in the auxiliary chamber 16 propagates relatively slowly into the main chamber 5 through the peripheral gap 22, which functions as a throttling portion. Figure 6 As shown, after the sub-chamber tube 11 is removed from the sub-chamber hole 17 and the sub-chamber 16 is opened, the flame in the sub-chamber 16 directly propagates into the main chamber 5 .

[0071] As described above, in this embodiment, the flame propagation from the sub-chamber 16 to the main chamber 5 can be delayed, and the combustion angle (Burn angle) after ignition can be extended. Figure 3 As shown, the in-cylinder pressure can be slowly increased after ignition, the timing of the in-cylinder pressure peak can be delayed, and the high in-cylinder pressure can be maintained for a long time.

[0072] It is preferable to control the ignition timing θig so that the peak timing θpd at which the in-cylinder pressure peak pd occurs coincides with or is close to the timing at which the mechanical efficiency is maximized.

[0073] Figure 7 This shows the positions of the piston 2, connecting rod 25, and crankshaft 26 during the period when mechanical efficiency is maximized (referred to as the maximum mechanical efficiency period). During this period, the angle θ formed between the crankshaft radius R and the connecting rod center axis Cc is 90°. Therefore, the length r of the moment arm used to calculate the torque of the force applied to the crankshaft 26 is equal to the crankshaft radius R, and mechanical efficiency is maximized. Therefore, by controlling the ignition timing θig so that the peak in-cylinder pressure pd occurs during or near the maximum mechanical efficiency period, the engine's thermal efficiency can be improved.

[0074] Thus, the ECU 100 controls the ignition timing θig so that the peak in-cylinder pressure pd occurs when the angle θ formed by the crankshaft radius R and the connecting rod center axis Cc is 90° or approximately 90°. This timing is, for example, within the range of 10 to 80° after compression top dead center (CTDC), more preferably within the range of 45 to 80°. For example, in an engine with a connecting rod ratio of 3.1, the timing can be 70° after compression top dead center (CTDC).

[0075] On the other hand, regarding fuel injection control, ECU 100 injects fuel from injector 9 before the spark plug 10 ignites and before the sub-chamber tube 11 is inserted into the sub-chamber hole 17. This allows a mixture to be formed within the sub-chamber 16 and reliably ignited. At this time, ECU 100 injects fuel from injector 9 in an amount sufficient to prevent the mixture within the main chamber 5 and sub-chamber 16 from self-igniting before the spark plug 10 ignites. This amount, which prevents self-ignition, refers to an amount that prevents self-ignition during high-load operation, such as in an engine with a high compression ratio (compression ratio ε of 15 or greater), poor cooling efficiency, and a shape that easily generates hot spots within the combustion chamber.

[0076] The fuel injection timing in this embodiment is similar to the comparative example, and is during the intake stroke or before the intake stroke (e.g., during the exhaust stroke). Furthermore, if the injector is a direct injection injector, the fuel injection timing can be set during the intake stroke or the compression stroke. The fuel injection amount in this embodiment can be set to a smaller amount than that corresponding to the stoichiometric air-fuel ratio.

[0077] Furthermore, increasing the compression ratio is beneficial for improving engine thermal efficiency. However, excessively high compression ratios can cause knocking. Therefore, in this embodiment, as described above, the sub-chamber tube 11 is inserted into the sub-chamber hole 17 to form the sub-chamber 16. This allows the compression ratio of the sub-chamber 16 to be substantially lower than that of the main chamber 5, thus suppressing knocking caused by the high compression ratio.

[0078] Figure 8 The comparative example is shown. Figure 9 and Figure 10 In each figure, state A represents the compression bottom dead center, state C represents the compression top dead center, and state B represents the intermediate timing state.

[0079] First, in Figure 8 In the comparative example shown, the sub-chamber tube 11 and sub-chamber hole 17 are not provided. YA, YB, and YC are the distances from the cylinder head 4 to the piston upper surface 6. YA = 10YC, YB = 5YC = (1 / 2)YA. Regarding the compression ratio ε, for convenience, it can be assumed that ε = 1 in state A, ε = 2 in state B, and ε = 10 in state C.

[0080] Next, explain Figure 9 The first embodiment of this embodiment is shown. The relationships among YA, YB, and YC are the same as described above: YA = 10YC, YB = 5YC = (1 / 2)YA. Meanwhile, ZA, ZB, and ZC are the distances from the cylinder head 4 to the sub-chamber bore bottom 18: ZA = 15YC, ZB = 10YC, and ZC = 6YC. Furthermore, the depth Z of the sub-chamber bore 17 is 5YC.

[0081] Consider the main chamber 5 divided into a main chamber region R1 located radially outward directly above the piston upper surface 6 and a sub-chamber region R2 located radially inward directly above the sub-chamber bore bottom surface 18. In state A, the compression ratios of both main chamber region R1 and sub-chamber region R2 are ε = 1.

[0082] In state B, the lower end surface 12 of the sub-chamber tube 11 is at the same height as the piston upper surface 6, and the sub-chamber tube 11 has just begun to be inserted into the sub-chamber hole 17. At this time, the compression ratios of the main chamber region R1 and the sub-chamber region R2 are also equal, ε=2.

[0083] After this time, since the sub-chamber tube 11 is inserted into the sub-chamber hole 17, the sub-chamber 16 is substantially separated from the main chamber 5. Furthermore, the interiors of the two chambers are compressed.

[0084] In state C, the compression ratio of the main chamber region R1, or the main chamber 5, is ε = 10, similar to the comparative example. Meanwhile, since compression of the sub-chamber region R2, or the sub-chamber 16, begins substantially in state B, its compression ratio is ε = 2 × (ZB / ZC) = 3.33. Consequently, the compression ratio of the sub-chamber 16 can be lowered compared to that of the main chamber 5, suppressing knocking caused by the increased compression ratio.

[0085] also, Figure 9 The first embodiment shown can significantly reduce the compression ratio of the sub chamber 16 compared to the compression ratio of the main chamber 5 , but the depth Z of the sub chamber hole 17 increases, and the length L of the piston 2 increases, which is not preferable in terms of engine packaging.

[0086] Therefore, the solution to this problem is Figure 10 The second example of this embodiment is shown below.

[0087] As described above, YA = 10YC. However, unlike the first embodiment, YB is YB = 2YC = (1 / 5)YA. Meanwhile, the distance from the cylinder head 4 to the sub-chamber bore bottom 18 is ZA = 12YC, ZB = 4YC, and ZC = 3YC. The depth Z of the sub-chamber bore 17 is 2YC.

[0088] In this case, in state A, the compression ratios of both the main chamber region R1 and the sub-chamber region R2 are ε=1.

[0089] exist Figure 10 In state B, Figure 9 Similarly, in state B, the sub-chamber tube 11 is just beginning to be inserted into the sub-chamber hole 17. At this time, the compression ratios of the main chamber region R1 and the sub-chamber region R2 are equal, ε=5.

[0090] In state C, the compression ratio of the main chamber 5 is ε = 10, similar to the comparative example. Meanwhile, the compression ratio of the sub chamber 16 is ε = 5 × (ZB / ZC) = 6.66. Therefore, the compression ratio of the sub chamber 16 can be lowered compared to that of the main chamber 5, suppressing knocking caused by the increased compression ratio.

[0091] This embodiment and Figure 9 Compared to the first embodiment shown, the compression ratio of the sub-chamber 16 decreases less than that of the main chamber 5, but the depth Z of the sub-chamber hole 17 can be reduced and the length L of the piston 2 can be shortened. Therefore, preferred engine packaging can be achieved.

[0092] According to this embodiment, the compression ratio of the sub-chamber 16 can be lowered compared to that of the main chamber 5. This not only suppresses knock but also reduces the ignition energy in the spark plug 10 (specifically, the ignition coil secondary voltage applied to the spark plug 10). This is because the gas density is lower at a low compression ratio. Furthermore, this reduction in ignition energy can suppress the growth rate of the flame kernel after ignition in the sub-chamber 16. Suppressing the flame kernel growth rate also delays flame propagation from the sub-chamber 16 to the main chamber 5, as well as flame propagation within the main chamber 5. This helps to bring the timing of the cylinder pressure peak θpd closer to the period of maximum mechanical efficiency.

[0093] In addition, if Figure 2 and Figure 5 As shown, after ignition, the piston 2 descends, and the flame within the sub-chamber 16 propagates into the main chamber 5 through the peripheral gap 22. The size of the peripheral gap 22 is set to the minimum required to prevent the inner surface of the sub-chamber bore 17 from colliding with the sub-chamber tube 11 even when the piston 2 swings. Therefore, the flame within the sub-chamber 16 propagates slowly into the main chamber 5 through the peripheral gap 22, which helps to keep the peak in-cylinder pressure (θpd) close to the period of maximum mechanical efficiency.

[0094] Since the outer diameter D1 of the auxiliary chamber tube 11 and the inner diameter d2 of the auxiliary chamber bore 17 are constant, the size of the peripheral gap 22 can be maintained at a substantially constant, small value as described above, after ignition and while the piston is descending. Consequently, the flame propagation speed from the auxiliary chamber 16 to the main chamber 5 can be kept low until the auxiliary chamber tube 11 is removed from the auxiliary chamber bore 17.

[0095] In addition, for example Figure 9 In the example, when compressing from state B to state C, the actual compression ratio will not be as described above due to compression leakage from the sub chamber 16 through the peripheral gap 22. However, since the actual compression is performed at a high speed, the compression ratio calculated as described above is appropriate to a certain extent.

[0096] In addition, even if the peak in-cylinder pressure of this embodiment is lower than that of the comparative example, since the peak in-cylinder pressure pd is generated during or near the period of maximum mechanical efficiency in this embodiment, the generated engine torque, that is, the thermal efficiency of the engine, can be improved compared with the comparative example.

[0097] Furthermore, the ignition timing θig does not necessarily need to be such that the peak period θpd coincides with or is near the period of maximum mechanical efficiency. It may also be such that the peak period θpd is earlier than or is near the period of maximum mechanical efficiency. This still allows the peak period θpd to be closer to the period of maximum mechanical efficiency than in the comparative example, which is beneficial for improving thermal efficiency.

[0098] As described above, according to the present embodiment, it is possible to provide an engine system and a method for controlling an internal combustion engine that are advantageous for improving the thermal efficiency of the internal combustion engine.

[0099] Although the embodiments of the present disclosure have been described in detail above, the present disclosure may also have other embodiments and modifications.

[0100] (1) For example, the cross-sectional shape perpendicular to the axial direction of the auxiliary chamber tube 11 and the auxiliary chamber hole 17 may be other than circular, and may be polygonal, such as an ellipse or a quadrilateral.

[0101] (2) Figures 8 to 10 The compression ratio values ​​shown in the example are just examples. These values ​​can be changed arbitrarily.

[0102] The embodiments of the present disclosure are not limited to the embodiments described above, and all modifications, applications, and equivalents included in the concept of the present disclosure as defined by the scope of protection are included in the present disclosure. Therefore, the present disclosure should not be interpreted in a limiting sense, but can also be applied to any other technology within the scope of the concept of the present disclosure.

[0103] This application is based on Japanese patent application (Japanese Patent Application No. 2020-135842) filed on August 11, 2020, the contents of which are incorporated herein by reference.

[0104] Industrial Availability

[0105] The engine system and the control method of the internal combustion engine disclosed herein are beneficial to improving the thermal efficiency of the internal combustion engine.

[0106] Description of Reference Numerals

[0107] 1 Internal combustion engine

[0108] 2 pistons

[0109] 3 cylinders

[0110] 4 cylinder heads

[0111] 5 Main Room

[0112] 9 Injector

[0113] 10 Spark plugs

[0114] 11 Deputy Chamber Tube

[0115] 17 auxiliary chamber hole

[0116] 100 Electronic Control Units (ECUs)

Claims

1. An engine system comprising an internal combustion engine and a control unit. The internal combustion engine comprises: a main chamber defined by the piston, cylinder, and cylinder head; a spark plug mounted on the cylinder head; a secondary chamber pipe surrounding the spark plug and protruding downward from the cylinder head; a secondary chamber hole formed in the piston and capable of receiving the secondary chamber tube; as well as an injector that injects the fuel supplied into the main chamber, The control unit is configured to control the ignition timing of the spark plug and the injection amount and injection timing of the injector. The control unit ignites the spark plug when the sub-chamber tube is inserted into the sub-chamber hole. The control unit causes the fuel to be injected from the injector before the spark plug is ignited and before the sub-chamber tube is inserted into the sub-chamber hole. The control unit controls the ignition timing so that a peak in-cylinder pressure generated after ignition of the spark plug occurs at a timing at which an angle formed by a crankshaft radius and a connecting rod center axis is 90° or in the vicinity of 90°.

2. The engine system according to claim 1, The timing at which the peak of the in-cylinder pressure occurs is a timing within a range of 10 to 80 degrees after compression top dead center.

3. The engine system according to claim 1 or 2, The sub-chamber tube has a certain outer diameter, and the sub-chamber hole has a certain inner diameter that is larger than the outer diameter of the sub-chamber tube.

4. A method for controlling an internal combustion engine, the internal combustion engine comprising: a main chamber defined by the piston, cylinder, and cylinder head; a spark plug mounted on the cylinder head; a secondary chamber pipe surrounding the spark plug and protruding downward from the cylinder head; as well as a secondary chamber hole formed in the piston and capable of receiving the secondary chamber tube; as well as an injector that injects the fuel supplied into the main chamber, The control method of the internal combustion engine comprises: a first step of injecting fuel from the injector before the spark plug is ignited and before the sub-chamber tube is inserted into the sub-chamber hole; as well as The second step of igniting the spark plug when the sub-chamber tube is inserted into the sub-chamber hole, The ignition timing is controlled so that a peak in-cylinder pressure generated after the spark plug is ignited occurs at a timing when an angle formed by a crankshaft radius and a connecting rod center axis is 90° or in the vicinity of 90°.

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