JP2020084767A - Internal combustion engine system - Google Patents

Abstract

To provide an internal combustion engine system capable of improving combustibility of compressed natural gas that is fuel for combustion when an engine load is low.SOLUTION: An internal combustion engine system for mixing and burning light oil and compressed natural gas in a combustion chamber includes: an intake valve provided between an intake passage and the combustion chamber; and a control section controlling opening/closing timing of the intake valve in accordance with an engine load of an internal combustion engine. In the internal combustion engine system, when the engine load of the internal combustion engine is equal to or lower than a predetermined engine load, the control section delays timing of closing the intake valve compared to when the engine load is higher than the predetermined engine load.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an internal combustion engine system that uses compressed natural gas (CNG) as a fuel.

BACKGROUND ART Conventionally, an internal combustion engine that uses CNG as fuel has been known (for example, see Patent Document 1). Patent Document 1 discloses an internal combustion engine that injects light oil, which is a fuel for ignition, into a cylinder to ignite it, and burns CNG, which is a fuel for combustion.

JP2012-149537A

However, the internal combustion engine described in Patent Document 1 has a problem that when the engine load is low, CNG, which is a fuel for combustion, cannot be reliably burned, resulting in deterioration of fuel consumption and discharge of non-burnable fuel. It was In order to deal with such a problem, a method of using ignition fuel for combustion when the engine load is low can be considered, but such a method has room for improvement in terms of fuel consumption.

An object of the present disclosure is to provide an internal combustion engine system that can improve the combustibility of compressed natural gas, which is a fuel for combustion, when the engine load is low.

An internal combustion engine system according to an aspect of the present disclosure is an internal combustion engine system in which light oil and compressed natural gas are mixed and burned in a combustion chamber, and an intake valve provided between an intake passage and the combustion chamber, A control unit that controls the opening/closing timing of the intake valve in accordance with the engine load of the internal combustion engine; and the control unit, when the engine load of the internal combustion engine is a predetermined engine load or less, An internal combustion engine system that delays the timing of closing the intake valve as compared with the case where the engine load is higher than the predetermined engine load.

According to the internal combustion engine system of the present disclosure, it is possible to improve the combustibility of compressed natural gas that is a fuel for combustion when the engine load is low.

FIG. 1 is a diagram showing an internal combustion engine system according to the first embodiment. FIG. 2 is a flowchart showing the operation of the control unit. FIG. 3 is a time chart showing the operation of the intake valve, the exhaust valve, and the injector. FIG. 4 is a diagram showing an internal combustion engine system according to the second embodiment. FIG. 5 is a flowchart showing the operation of the control unit. FIG. 6 is a time chart showing the operation of the intake valve, the exhaust valve, and the injector.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiment described below is an example, and the present disclosure is not limited to this embodiment.

(First embodiment)
An internal combustion engine system 1 according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram showing an internal combustion engine system 1 according to the first embodiment. The internal combustion engine system 1 includes an internal combustion engine 10 and its fuel supply system and intake/exhaust system.

The cylinder block 11 of the internal combustion engine 10 is provided with a plurality of cylinders 12. Note that FIG. 1 shows only one cylinder 12. A piston 13 is provided in the cylinder 12. The piston 13 is connected to the crankshaft via a connecting rod, and moves up and down in the cylinder 12 according to the rotation of the crankshaft. An injector 15, an intake valve 16 and an exhaust valve 17 are provided for each cylinder 12 in a cylinder head 14 that covers the upper portion of the cylinder block 11.

The injector 15 is, for example, a piezo-type injector, and injects light oil, which is a fuel for ignition, into the cylinder 12. Injection of light oil from the injector 15 is controlled by the control unit 70 (described later).

The intake valve 16 includes a variable valve timing mechanism. The opening timing and closing timing of the intake valve 16 are controlled by the control unit 70. The exhaust valve 17 includes a variable valve timing mechanism. The opening timing and the closing timing of the exhaust valve 17 are controlled by the control unit 70. A combustion chamber 19 is formed by a space surrounded by the inner wall 18 of the cylinder 12, the piston 13 and the cylinder head 14.

The air supplied to the internal combustion engine 10 passes through an air cleaner (not shown) and is mixed with CNG in an intake manifold (an example of an “intake pipe”) 20 to form a mixture. The air-fuel mixture is introduced into the cylinder 12 via the intake valve 16. The air-fuel mixture introduced into the cylinder 12 is compressed in the cylinder 12. When light oil is injected from the injector 15 in this state, the light oil serves as an ignition source and the CNG burns. Exhaust gas from the internal combustion engine 10 is exhausted to the exhaust manifold 30 via the exhaust valve 17, and is exhausted to the outside through an exhaust purification device, a silencer, etc. (not shown).

CNG is supplied from the tank 40 into the intake manifold 20 through the supply path 50. The supply path 50 includes a pipe 51, a regulator 52, a pipe 53, and an injector 54. The pipe 51 connects the tank 40 and the regulator 52. The first end of the pipe 51 is connected to the tank 40. The second end of the pipe 51 is connected to the regulator 52. The CNG stored in the tank 40 is supplied to the regulator 52 through the inside of the pipe 51.

The regulator 52 reduces the pressure of CNG supplied from the tank 40 to a predetermined pressure. The pipe 53 connects the regulator 52 and the injector 54. The first end of the pipe 53 is connected to the regulator 52. The second end of the pipe 53 is connected to the injector 54. The CNG depressurized to a predetermined pressure by the regulator 52 is supplied to the injector 54 through the inside of the pipe 53.

The injector 54 injects the CNG supplied from the regulator 52 into the intake manifold 20. The injection of CNG from the injector 54 is controlled by the control unit 70. The injector 54 injects CNG into the intake manifold 20, but since the intake manifold 20 is connected to the combustion chamber 19, the CNG injected into the intake manifold 20 is supplied to the combustion chamber 19. It That is, the injector 54 supplies CNG to the combustion chamber 19.

The internal combustion engine system 1 includes a control unit 70. The control unit 70 has, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like as hardware. Each function of the control unit 70 described below is realized by the CPU executing the computer program read from the ROM on the RAM.

A crank angle sensor 71 and an accelerator opening sensor 72 are electrically connected to the control unit 70. The crank angle sensor 71 detects the crank angle of the internal combustion engine 10. The accelerator opening sensor 72 detects the accelerator opening of the vehicle in which the internal combustion engine 10 is mounted. The crank angle signal from the crank angle sensor 71 and the accelerator opening signal from the accelerator opening sensor 72 are input to the control unit 70. The control unit 70 calculates the engine speed NE of the internal combustion engine 10 based on the crank angle signal. The control unit 70 also calculates the engine load QE of the internal combustion engine 10 based on the accelerator opening signal.

The injector 15, the intake valve 16, the exhaust valve 17, and the injector 54 are electrically connected to the control unit 70. The control unit 70 controls injection of light oil from the injector 15, opening/closing of the intake valve 16, opening/closing of the exhaust valve 17, and injection of CNG from the injector 54.

The injector 15, the intake valve 16, the exhaust valve 17, and the injector 54 are controlled based on the engine speed NE and the engine load QE of the internal combustion engine 10 according to a control map stored in advance in a storage unit included in the control unit 70. ..

When the engine load of the internal combustion engine 10 is low, the amount of light oil injected from the injector 15 is small. Therefore, it becomes difficult to burn CNG sufficiently in the cylinder 12. Therefore, in the present embodiment, the opening/closing timing of the intake valve 16 is changed depending on whether the engine load of the internal combustion engine 10 is low or not. Thereby, when the engine load of the internal combustion engine 10 is low, the combustibility of the compressed natural gas that is the fuel for combustion is improved.

The operation of the control unit 70 will be described with reference to FIG. FIG. 2 is a flowchart showing the operation of the control unit 70. The flowchart shown in FIG. 2 is repeatedly executed at a predetermined cycle.

In step S1, the control unit 70 calculates the engine speed NE of the internal combustion engine 10 based on the crank angle signal input from the crank angle sensor 71. Further, the control unit 70 calculates the engine load QE of the internal combustion engine 10 based on the accelerator opening signal input from the accelerator opening sensor 72.

In step S2 following step S1, the control unit 70 determines whether the engine load QE is equal to or less than a predetermined engine load QE ₀ . The predetermined engine load QE ₀ is a threshold for determining whether or not to execute the control for reliably burning CNG, and is obtained in advance by experiments, simulations, etc., and stored in the storage unit of the control unit 70. Remembered

When it is determined in step S2 that the engine load QE is less than or equal to the predetermined engine load QE ₀ (step S2: YES), the process proceeds to step S3. Then, in step S3, the control unit 70 sets the opening/closing pattern of the intake valve 16 to the first opening/closing pattern, and ends the process.

When it is determined in step S2 that the engine load QE is not equal to or less than the predetermined engine load QE ₀ (step S2: NO), the process proceeds to step S4. Then, in step S4, the control unit 70 sets the opening/closing pattern of the intake valve 16 to the second opening/closing pattern, and ends the process.

The first opening/closing pattern and the second opening/closing pattern will be described with reference to FIG. First, the second opening/closing pattern will be described. As described above, the second opening/closing pattern is set when it is determined that the engine load QE is not less than or equal to the predetermined engine load QE ₀ .

The exhaust valve 17 is opened at a timing (time t1) before the piston 13 reaches the bottom dead center in the combustion process. The exhaust valve 17 is left open during the exhaust stroke, and is closed at the timing (time t5) immediately after the piston 13 begins to descend from the top dead center during the intake stroke.

The intake valve 16 is opened at the timing (time t3) before the piston 13 reaches the top dead center in the exhaust stroke. Therefore, from time t3 to time t5, both the intake valve 16 and the exhaust valve 17 are open. The intake valve 16 is kept open during the intake stroke, and is closed at the timing (time t6) after the piston 13 starts rising from the bottom dead center in the compression stroke.

In the exhaust stroke, the injector 54 injects CNG into the intake manifold 20 from the timing immediately before the intake valve 16 is opened (time t2) to the timing when the piston 13 reaches the top dead center (time t4). The CNG injected into the intake manifold 20 is mixed with air to form an air-fuel mixture. The air-fuel mixture is introduced into the cylinder 12 via the intake valve 16 as the piston 13 descends. After the piston 13 reaches the bottom dead center, the intake valve 16 is closed as described above, and the air-fuel mixture in the combustion chamber 19 is compressed as the piston 13 rises.

In the compression stroke, the injector 15 injects light oil into the cylinder 12 at the timing (time t7 to t8) immediately before the piston 13 reaches the top dead center. The light oil injected into the cylinder 12 serves as an ignition source, and the CNG burns. Then, as described above, the exhaust valve 17 is opened in the final stage of the combustion stroke, and the exhaust gas is discharged from the inside of the cylinder 12 via the exhaust valve 17 as the piston 13 rises.

Next, the first opening/closing pattern will be described. As described above, the first opening/closing pattern is set when it is determined that the engine load QE is less than or equal to the predetermined engine load QE ₀ .

The opening/closing timing of the exhaust valve 17 is similar to the second opening/closing pattern. That is, the exhaust valve 17 is opened at the timing (time t1) before the piston 13 reaches the bottom dead center in the combustion stroke, and at the timing immediately after the piston 13 starts to descend from the top dead center in the intake stroke. It is closed at (time t5).

The intake valve 16 is opened at a timing (time t9) after a predetermined time has elapsed since the exhaust valve 17 was closed in the intake stroke. The intake valve 16 is closed at the timing (time t11) when the piston 13 reaches a substantially intermediate position between the bottom dead center and the top dead center in the compression stroke.

The injection timing of CNG from the injector 54 is the same as the second opening/closing pattern. That is, the injector 54 injects CNG into the intake manifold 20 from the timing immediately before the intake valve 16 is opened (time t2) to the timing when the piston 13 reaches the top dead center (time t4) in the exhaust stroke. The CNG injected into the intake manifold 20 is mixed with air to form an air-fuel mixture.

The air-fuel mixture is introduced into the cylinder 12 via the intake valve 16 as the piston 13 descends after the intake valve 16 is opened. The temperature of the air-fuel mixture introduced into the cylinder 12 rises due to heat exchange with the piston 13 and the inner wall 18 (“heat exchange step” in FIG. 3).

As described above, in the first opening/closing pattern, the intake valve 16 is kept open until the timing (time t11) when the piston 13 reaches the substantially intermediate position between the bottom dead center and the top dead center in the compression stroke. Therefore, from the timing when the piston 13 reaches the bottom dead center (time t10) to the timing when the piston 13 reaches the substantially intermediate position between the bottom dead center and the top dead center (time t11), the air-fuel mixture enters the intake manifold 20. (Intake return stroke in FIG. 3). The air-fuel mixture remaining in the combustion chamber 19 without being returned to the intake manifold 20 is compressed by closing the intake valve 16 and moving up the piston 13.

The injection timing of the light oil from the injector 15 is the same as the second opening/closing pattern. That is, in the compression stroke, light oil is injected into the cylinder 12 at the timing (time t7 to t8) immediately before the piston 13 reaches the top dead center. The light oil injected into the cylinder 12 serves as an ignition source, and the CNG burns. Then, as described above, the exhaust valve 17 is opened in the final stage of the combustion stroke, and the exhaust gas is discharged from the inside of the cylinder 12 via the exhaust valve 17 as the piston 13 rises.

The high-temperature air-fuel mixture returned to the intake manifold 20 is introduced into the cylinder 12 in the intake stroke performed in another cylinder and used for combustion. In this way, by using the high temperature mixture returned to the intake manifold 20 in the nth compression stroke for the (n+1)th combustion, the combustibility of the compressed natural gas is improved when the engine load is low. You can Note that n is a natural number.

As described above, the internal combustion engine system 1 according to the first embodiment is the internal combustion engine system 1 in which light oil and compressed natural gas are mixed and burned in the combustion chamber 19, and between the intake manifold 20 and the combustion chamber 19. And a control unit 70 that controls the opening/closing timing of the intake valve 16 according to the engine load of the internal combustion engine 10. The control unit 70 determines the engine load of the internal combustion engine 10 in advance. and when a predetermined engine load QE ₀ or less, than when the engine load is higher than a predetermined engine load QE _0, slowing the intake valve 16 closes timing, an internal combustion engine system 1.

As a result, the air-fuel mixture that has become hot due to heat exchange with the piston 13 and the inner wall 18 in the combustion chamber 19 can be returned to the intake manifold 20.

Therefore, the high temperature air-fuel mixture returned to the intake manifold 20 in the n-th compression stroke can be used for the (n+1)-th combustion in the other cylinders, and the combustibility of the compressed natural gas is improved when the engine load is low. Can be made

Further, in the first embodiment, when the engine load is higher than the predetermined engine load QE ₀ , the control unit 70 has the intake valve 16 provided between the combustion chamber 19 and the exhaust manifold 30 in the exhaust stroke. When the exhaust valve 17 is opened, the piston 13 is controlled so as to be closed during the compression stroke from the bottom dead center to the top dead center. When the engine load is equal to or lower than the predetermined engine load QE _0, The intake valve 16 is controlled to be opened after the exhaust valve 17 is closed in the intake stroke and closed at a timing later than when the engine load is higher than the predetermined engine load QE ₀ in the compression stroke.

As a result, the air-fuel mixture that has become hot due to heat exchange with the piston 13 and the inner wall 18 in the combustion chamber 19 moves from the timing when the piston 13 reaches the bottom dead center (time t10) to when the piston 13 reaches the bottom dead center. It is returned to the inside of the intake manifold 20 until the timing (time t11) when it reaches a position approximately midway from the dead point.

Therefore, the hot air-fuel mixture can be reliably returned to the inside of the intake manifold 20, and the combustibility of the compressed natural gas can be further improved when the engine load is low.

In the first embodiment, the case where the opening/closing timing of the intake valve 16 is changed according to the engine load of the internal combustion engine 10 has been described as an example, but the present invention is not limited to this. In addition to changing the opening/closing timing of the intake valve 16, the opening/closing timing of the exhaust valve 17, the injection timing of light oil from the injector 15, the injection timing of CNG from the injector 54, and the like may be changed.

(Second embodiment)
An internal combustion engine system 101 according to the second embodiment will be described with reference to FIG. FIG. 4 is a diagram showing an internal combustion engine system 101 according to the second embodiment. The internal combustion engine system 101 includes an internal combustion engine 110, and a fuel supply system and an intake/exhaust system thereof.

The cylinder block 111 of the internal combustion engine 110 is provided with a plurality of cylinders 112. In addition, in FIG. 4, only one cylinder 112 is shown. A piston 113 is provided in the cylinder 112. The piston 113 is connected to the crankshaft via a connecting rod, and moves up and down in the cylinder 112 according to the rotation of the crankshaft. An injector 115, an injector 154, an intake valve 116, and an exhaust valve 117 are provided for each cylinder 112 in a cylinder head 114 that covers the upper portion of the cylinder block 111.

The injector 115 is, for example, a piezo-type injector, and injects light oil, which is a fuel for ignition, into the cylinder 112. The injection of light oil from the injector 115 is controlled by the control unit 170 (described later).

The intake valve 116 includes a variable valve timing mechanism. The opening timing and the closing timing of the intake valve 116 are controlled by the control unit 170. The exhaust valve 117 includes a variable valve timing mechanism. The opening timing and closing timing of the exhaust valve 117 are controlled by the control unit 170. A combustion chamber 119 is formed by a space surrounded by the inner wall 118 of the cylinder 112, the piston 113, and the cylinder head 114.

Air supplied to the internal combustion engine 110 passes through an air cleaner and an intake manifold (an example of an “intake pipe”) and is introduced into the cylinder 112 via an intake valve 116. The air introduced into the cylinder 112 is mixed with the CNG injected from the injector 154 in the cylinder 112 to form an air-fuel mixture. The air-fuel mixture is compressed in the cylinder 112. When light oil is injected from the injector 115 in this state, the light oil serves as an ignition source and the CNG burns. Exhaust gas from the internal combustion engine 110 is discharged to the exhaust manifold 130 via the exhaust valve 117, and is discharged to the outside through an exhaust gas purification device, a silencer device (not shown), and the like.

CNG is supplied from the tank 140 into the cylinder 112 through the supply path 150. The supply path 150 includes a pipe 151, a regulator 152, a pipe 153, and an injector 154. The pipe 151 connects the tank 140 and the regulator 152. The first end of the pipe 151 is connected to the tank 140. The second end of the pipe 151 is connected to the regulator 152. The CNG stored in the tank 140 is supplied to the regulator 152 through the inside of the pipe 151.

The regulator 152 reduces the pressure of CNG supplied from the tank 140 to a predetermined pressure. The pipe 153 connects the regulator 152 and the injector 154. The first end of the pipe 153 is connected to the regulator 152. The second end of the pipe 153 is connected to the injector 154. The CNG depressurized to a predetermined pressure by the regulator 152 is supplied to the injector 154 through the inside of the pipe 153.

The injector 154 injects the CNG supplied from the regulator 152 into the cylinder 112. That is, the injector 154 supplies CNG to the combustion chamber 119. The injection of CNG from the injector 154 is controlled by the controller 170.

In addition, in the present embodiment, an example is described in which light oil is injected from the injector 115 into the cylinder 112 and compressed natural gas is injected from the injector 154 into the cylinder 112, but the present invention is not limited to this. For example, light oil and compressed natural gas may be injected into the cylinder 112 from a common injector.

The internal combustion engine system 101 includes a control unit 170. The control unit 170 has, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like as hardware. Each function of the control unit 170 described below is realized by the CPU executing the computer program read from the ROM on the RAM.

A crank angle sensor 171 and an accelerator opening sensor 172 are electrically connected to the control unit 170. The crank angle sensor 171 detects the crank angle of the internal combustion engine 110. The accelerator opening sensor 172 detects the accelerator opening of the vehicle in which the internal combustion engine 110 is mounted. The crank angle signal from the crank angle sensor 171 and the accelerator opening signal from the accelerator opening sensor 172 are input to the control unit 170. The control unit 170 calculates the engine speed NE of the internal combustion engine 110 based on the crank angle signal. The control unit 170 also calculates the engine load QE of the internal combustion engine 110 based on the accelerator opening signal.

The injector 115, the intake valve 116, the exhaust valve 117, and the injector 154 are electrically connected to the control unit 170. The control unit 170 controls injection of light oil from the injector 115, opening/closing of the intake valve 116, opening/closing of the exhaust valve 117, and injection of CNG from the injector 154.

The injector 115, the intake valve 116, the exhaust valve 117, and the injector 154 are controlled based on the engine speed NE and the engine load QE of the internal combustion engine 110 according to a control map stored in advance in a storage unit included in the control unit 170. ..

When the engine load of the internal combustion engine 110 is low, the amount of light oil injected from the injector 115 is small. Therefore, it becomes difficult to burn CNG sufficiently in the cylinder 112. Therefore, in the present embodiment, the opening/closing timing of the intake valve 116, the timing of injecting light oil from the injector 115, and the injection of compressed natural gas from the injector 154 depending on whether the engine load of the internal combustion engine 110 is low or not. I am trying to change the timing. As a result, when the engine load of the internal combustion engine 110 is low, the combustibility of the compressed natural gas that is the fuel for combustion is improved.

The operation of the controller 170 will be described with reference to FIG. FIG. 5 is a flowchart showing the operation of the control unit 170. The flowchart shown in FIG. 5 is repeatedly executed at a predetermined cycle.

In step S11, the control unit 170 calculates the engine speed NE of the internal combustion engine 110 based on the crank angle signal input from the crank angle sensor 171. Further, the control unit 170 calculates the engine load QE of the internal combustion engine 110 based on the accelerator opening signal input from the accelerator opening sensor 172.

In step S12 following the step S11, the control unit 170, the engine load QE determines whether a predetermined engine load QE ₀ or less. It should be noted that the predetermined engine load QE ₀ is a threshold value for determining whether or not to execute the control for reliably burning CNG, and is obtained in advance by experiments, simulations, etc., and stored in the storage unit of the control unit 170. Remembered

When it is determined in step S12 that the engine load QE is less than or equal to the predetermined engine load QE ₀ (step S12: YES), the process proceeds to step S13. Then, in step S13, control unit 170 sets the opening/closing pattern of intake valve 116 to the third opening/closing pattern.

In step S14 subsequent to step S13, the control unit 170 sets the pattern of light oil injection from the injector 115 and the injection of CNG from the injector 154 to the first injection pattern. The process ends after the process of step S14.

When it is determined in step S12 that the engine load QE is not equal to or less than the predetermined engine load QE ₀ (step S12: NO), the process proceeds to step S15. Then, in step S15, control unit 170 sets the opening/closing pattern of intake valve 116 to the fourth opening/closing pattern.

In step S16 subsequent to step S15, the control unit 170 sets the pattern of light oil injection from the injector 115 and the injection of CNG from the injector 154 to the second injection pattern. The process ends after the process of step S16.

The third opening/closing pattern, the fourth opening/closing pattern, the first injection pattern, and the second injection pattern will be described with reference to FIG. 6. First, the fourth opening/closing pattern and the second injection pattern will be described. As described above, the fourth opening/closing pattern and the second injection pattern are set when it is determined that the engine load QE is not equal to or less than the predetermined engine load QE ₀ .

The exhaust valve 117 is opened at a timing (time t21) before the piston 113 reaches the bottom dead center in the combustion stroke. The exhaust valve 117 is kept open during the exhaust stroke, and is closed at the timing (time t23) immediately after the piston 113 starts descending from the top dead center during the intake stroke.

The intake valve 116 is opened at the timing (time t22) before the piston 113 reaches the top dead center in the exhaust stroke. Therefore, from time t22 to time t23, both the intake valve 116 and the exhaust valve 117 are open. The intake valve 116 is kept open during the intake stroke, and is closed at the timing (time t24) after the piston 113 starts rising from the bottom dead center in the compression stroke.

The injector 154 starts the combustion stroke from the timing (time t25) when the piston 113 is in the process of reaching from the bottom dead center to the top dead center in the compression stroke and the intake valve 116 and the exhaust valve 117 are both closed. CNG is injected into the cylinder 112 until an intermediate timing (time t28). The CNG injected into the cylinder 112 in a state where air is compressed is mixed with air to form an air-fuel mixture. Further, the light oil is injected from the injector 115 at the timing (time t26 to t27) in the middle of the piston 113 from the bottom dead center to the top dead center in the compression stroke, so that the CNG is burned with the light oil as the ignition source.

Next, the third opening/closing pattern and the first injection pattern will be described. As described above, the third opening/closing pattern and the first injection pattern are set when the engine load QE is determined to be equal to or less than the predetermined engine load QE ₀ .

The opening/closing timing of the exhaust valve 117 is similar to the fourth opening/closing pattern. That is, the exhaust valve 117 is opened at the timing (time t21) before the piston 113 reaches the bottom dead center in the combustion stroke, and at the timing immediately after the piston 113 starts descending from the top dead center in the intake stroke. It is closed at (time t23).

The intake valve 116 is opened at a timing (time t29) after a predetermined time has elapsed since the exhaust valve 117 was closed in the intake stroke. The intake valve 116 is closed at the timing (time t31) when the piston 113 reaches a substantially intermediate position between the bottom dead center and the top dead center in the compression stroke.

In the first injection pattern, the injection of CNG from the injector 154 is performed twice. In the injector 154, the injector 154 receives the first CNG in the cylinder 112 from the timing (time t32) when the piston 113 starts to descend from the top dead center to the timing (time t33) immediately before the intake valve 116 is opened. Inject.

The CNG injected into the cylinder 112 is mixed with the air introduced into the cylinder 112 when the intake valve 116 is opened to form an air-fuel mixture. Further, the temperature of the air-fuel mixture rises due to heat exchange with the piston 113 and the inner wall 118 (“heat exchange step” in FIG. 6).

As described above, in the third opening/closing pattern, the intake valve 116 remains open until the timing (time t31) when the piston 113 reaches the substantially intermediate position between the bottom dead center and the top dead center in the compression stroke. Therefore, from the timing (time t30) when the piston 113 reaches the bottom dead center to the timing (time t31) when the piston 113 reaches the substantially intermediate position between the bottom dead center and the top dead center, the intake air mixture 120 is discharged. (Intake return stroke in FIG. 6). The air-fuel mixture which is not returned to the intake manifold 120 and remains in the combustion chamber 119 is compressed by closing the intake valve 116 and raising the piston 113.

In the compression stroke, the injector 115 injects light oil into the cylinder 112 at the timing (time t34 to t35) immediately before the piston 113 reaches the top dead center. The light oil injected into the cylinder 112 serves as an ignition source, and the CNG burns.

Further, after the light oil is injected into the cylinder 112, CNG is injected from the injector 154 at the timing (time t36 to t37) immediately after the piston 113 starts to descend from the top dead center in the combustion stroke. As a result, the injected CNG burns. Then, as described above, the exhaust valve 117 is opened in the final stage of the combustion stroke, and the exhaust gas is discharged from the inside of the cylinder 112 via the exhaust valve 117 as the piston 113 rises.

The high-temperature air-fuel mixture returned to the intake manifold 120 is introduced into the cylinder 112 in the intake stroke performed in another cylinder and used for combustion. In this way, by using the high temperature air-fuel mixture returned into the intake manifold 120 in the nth compression stroke for the (n+1)th combustion, the combustibility of the compressed natural gas is improved when the engine load is low. You can

In the second embodiment in which CNG is directly injected into the cylinder 112, CNG is injected again into the combustion chamber 119 with the intake valve 116 closed after returning the air-fuel mixture into the intake manifold 120. You can Therefore, the amount of CNG used for combustion can be sufficiently secured while returning the high temperature air-fuel mixture into the intake manifold 120.

As described above, the internal combustion engine system 101 according to the second embodiment is the internal combustion engine system 101 in which light oil and compressed natural gas are mixed and burned in the combustion chamber 119, and between the intake manifold 120 and the combustion chamber 119. And a control unit 170 that controls the opening/closing timing of the intake valve 116 according to the engine load of the internal combustion engine 110. The control unit 170 determines the engine load of the internal combustion engine 110 in advance. and when a predetermined engine load QE ₀ or less, than when the engine load is higher than a predetermined engine load QE _0, slow the timing of closing the intake valve 116 is an internal combustion engine system 101.

As a result, the air-fuel mixture that has become hot due to heat exchange with the piston 113 and the inner wall 118 in the combustion chamber 119 can be returned to the intake manifold 120.

Therefore, the high-temperature air-fuel mixture returned to the intake manifold 120 in the n-th compression stroke can be used for the (n+1)-th combustion in other cylinders, and the combustibility of the compressed natural gas is improved when the engine load is low. Can be made

Further, in the second embodiment, the control unit 170 is provided with the intake valve 116 between the combustion chamber 119 and the exhaust manifold 130 in the exhaust stroke when the engine load is higher than the predetermined engine load QE ₀ . When the exhaust valve 117 is opened, the piston 113 is controlled to close during the compression stroke from the bottom dead center to the top dead center, and when the engine load is equal to or lower than the predetermined engine load QE _0. The intake valve 116 is controlled to be opened after the exhaust valve 117 is closed in the intake stroke and closed at a timing later than when the engine load is higher than a predetermined engine load QE ₀ in the compression stroke.

As a result, the temperature of the air-fuel mixture in the combustion chamber 119, which has become high due to heat exchange between the piston 113 and the inner wall 118, causes the piston 113 to reach the bottom dead center from the timing when the piston 113 reaches the bottom dead center (time t30). It is returned to the intake manifold 120 until the timing (time t31) when it reaches a position approximately midway from the dead point.

Therefore, the hot air-fuel mixture can be reliably returned to the inside of the intake manifold 120, and the combustibility of the compressed natural gas can be further improved when the engine load is low.

Further, in the second embodiment, an injector 154 for injecting compressed natural gas into the combustion chamber 119 and an injector 115 for injecting light oil into the combustion chamber 119 are provided, and the control unit 170 controls the load QE with a predetermined load. _When it is ₀ or less, the compressed natural gas is injected from the injector 154 immediately after the start of the intake stroke and immediately after the start of the combustion stroke, and the light oil is injected from the injector 115 immediately before the end of the compression stroke.

As a result, after returning the air-fuel mixture into the intake manifold 120, CNG is again injected into the combustion chamber 119 with the intake valve 116 closed.

Therefore, the amount of CNG used for combustion can be sufficiently secured while returning the high temperature air-fuel mixture into the intake manifold 120.

In the second embodiment, an example is described in which the opening/closing timing of the intake valve 116, the injection timing of light oil from the injector 115, and the injection timing of CNG from the injector 154 are changed according to the engine load of the internal combustion engine 110. However, the present invention is not limited to this, and the opening/closing timing of the exhaust valve 117 can be changed.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and may be appropriately modified and implemented without departing from the spirit of the present disclosure.

In each of the above-described embodiments, the case where the opening/closing timing of the intake valve is changed in two patterns according to the engine load has been described as an example, but the present invention is not limited to this. The control unit may change the opening/closing timing of the intake valve in a plurality of patterns of three or more according to the engine load, for example. Further, for example, the control unit may perform stepless control so that the closing timing of the intake valve is delayed as the engine load is lower.

According to the internal combustion engine system of the present disclosure, when the engine load is low, the combustibility of compressed natural gas, which is a fuel for combustion, can be improved, and its industrial applicability is great.

1, 101 Internal Combustion Engine System 10, 110 Internal Combustion Engine 11, 111 Cylinder Block 12, 112 Cylinder 13, 113 Piston 14, 114 Cylinder Head 15, 115 Injector 16, 116 Intake Valve 17, 117 Exhaust Valve 18, 118 Inner Wall 19, 119 Combustion chamber 20,120 Intake manifold 30,130 Exhaust manifold 40,140 Tank 50,150 Supply path 51,53,151,153 Piping 52,152 Regulator 54,154 Injector 70,170 Control unit 71,171 Crank angle sensor 72, 172 Accelerator opening sensor

Claims (4)

An internal combustion engine system for mixing and burning light oil and compressed natural gas in a combustion chamber,
An intake valve provided between the intake passage and the combustion chamber,
A control unit that controls the opening/closing timing of the intake valve according to the engine load of the internal combustion engine;
When the engine load of the internal combustion engine is less than or equal to a predetermined engine load, the control unit delays the timing of closing the intake valve as compared with the case where the engine load is higher than the predetermined engine load. ,
Internal combustion engine system. The control unit is
When the engine load is higher than the predetermined engine load, the intake valve is opened during the exhaust stroke while the exhaust valve provided between the combustion chamber and the exhaust passage is open, and the compression stroke In, the piston of the internal combustion engine is controlled to close on the way from bottom dead center to top dead center,
When the engine load is equal to or lower than the predetermined engine load, the intake valve is opened after the exhaust valve is closed in the intake stroke, and the engine load is higher than the predetermined engine load in the compression stroke. Control to close at a later time,
The internal combustion engine system according to claim 1. A first injector for injecting the compressed natural gas into the intake passage, and a second injector for injecting the light oil into the combustion chamber,
The control unit injects the compressed natural gas from the first injector from the middle to the end of the exhaust stroke, and injects the light oil from the second injector at a timing when the intake valve is closed in the compression stroke. Let
The internal combustion engine system according to claim 2. A third injector for injecting the compressed natural gas into the combustion chamber, and a fourth injector for injecting the light oil into the combustion chamber,
When the engine load is equal to or less than the predetermined engine load, the control unit causes the third injector to inject the compressed natural gas at a timing before the intake valve opens in the intake stroke, and in the compression stroke. After injecting the light oil from the fourth injector at a timing when the intake valve is closed, the compressed natural gas is again injected from the third injector in a combustion stroke.
The internal combustion engine system according to claim 2.

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