Control system

Abstract

To appropriately burn an air-fuel mixture.SOLUTION: A control system S includes: a sensor 4 that is provided in an engine 2 using an air-fuel mixture of natural gas obtained through vaporization of liquefied natural gas containing methane and intake air, and detects a feature amount indicating a combustion state in a combustion chamber of the engine 2 at predetermined intervals; an acquisition section 721 that acquires the feature amount detected by the sensor 4 and a phase in a combustion cycle of the engine 2 corresponding to the feature amount while associating them with each other; a specification section 722 that specifies a maximum phase corresponding to a maximum value of an increase rate of the feature amount on the basis of the plurality of feature amounts detected in one combustion cycle and a phase associated with each of the feature amounts; and an ignition control section 723 that changes ignition timing to the air-fuel mixture so that the maximum phase falls within a predetermined range when the maximum phase is outside the predetermined range set as timing of causing the combustion in the combustion chamber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control system for controlling combustion in a combustion chamber of an engine. [Background technology]

[0002] Engines that use liquefied natural gas are known. Patent Document 1 discloses a technology in which liquefied natural gas delivered from a fuel container that stores the liquefied natural gas is vaporized and supplied to the engine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-144697 A Summary of the Invention [Problem to be solved by the invention]

[0004] The temperature of liquefied natural gas stored in a fuel container rises due to the inflow of heat from outside the fuel container. As the temperature of the liquefied natural gas rises, methane, which has a low boiling point, vaporizes, causing a change in the ratio of the components of the liquefied natural gas. This change in the ratio of the components of the liquefied natural gas changes the combustion state of the mixture of natural gas and intake air, which can sometimes prevent the mixture from burning properly.

[0005] The present invention has been made in consideration of these points, and has as its object to properly combust an air-fuel mixture. [Means for solving the problem]

[0006] One aspect of the present invention provides a control system that is provided in an engine that uses a mixture of intake air and vaporized natural gas containing methane liquefied natural gas, and includes a sensor that detects at predetermined intervals a characteristic quantity that indicates the combustion state in the combustion chamber of the engine; an acquisition unit that acquires and correlates the characteristic quantity detected by the sensor with a phase in the combustion cycle of the engine that corresponds to the characteristic quantity; an identification unit that identifies a maximum phase that corresponds to a maximum value of the rate of increase of the characteristic quantity based on a plurality of the characteristic quantities detected during one combustion cycle and the phases associated with each of the characteristic quantities; and an ignition control unit that, when the maximum phase is outside a predetermined range that is set as the timing for combustion in the combustion chamber, changes the timing of ignition of the mixture so that the maximum phase is within the predetermined range.

[0007] The sensor may be an acceleration sensor that detects the acceleration of vibration of the cylinder in the sliding direction of a piston sliding inside the cylinder of the engine as the characteristic quantity, and the identification unit may identify the maximum phase at which the rate of increase of the acceleration is maximum.

[0008] The engine may have a plurality of sensors corresponding to each of a plurality of cylinders, each of the plurality of sensors detecting the acceleration of vibration in the sliding direction of the corresponding cylinder, the acquisition unit acquiring the acceleration of each of the plurality of cylinders and the phase corresponding to the acceleration from each sensor, the identification unit identifying the maximum phase for each cylinder, and the ignition control unit changing the ignition timing of a cylinder whose maximum phase is outside the predetermined range.

[0009] The predetermined range may be a range that includes a reference phase at which the piston of the engine is positioned at top dead center in the combustion stroke of the combustion cycle.

[0010] The ignition control unit may delay the ignition timing when the maximum phase is earlier than the predetermined range, and may advance the ignition timing when the maximum phase is later than the predetermined range.

[0011] The ignition control unit may change the ignition timing so that the maximum value of the rate of increase of the characteristic amount coincides with the reference phase. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an effect that the air-fuel mixture can be combusted appropriately. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram illustrating the configuration of a control system. [Figure 2] FIG. 2 is a diagram for explaining the configuration of a cylinder. [Figure 3] FIG. 4 is a diagram for explaining the relationship between the combustion state and acceleration. [Figure 4] FIG. 2 is a diagram for explaining the configuration of an ignition control device. [Figure 5] 10 is a flowchart illustrating an example of a process for changing ignition timing. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Configuration of Control System S] FIG. 1 is a diagram illustrating the configuration of a control system S. The control system S is a system for controlling combustion in a combustion chamber of an engine 2. The control system S is mounted on, for example, a vehicle or a ship. The control system S includes a container 1, an engine 2, an ignition plug 3, a sensor 4, an ignition control device 7, a supply pipe 11, a fuel injection unit 12, a cylinder 21, and an intake pipe 22.

[0015] Container 1 stores liquefied natural gas as fuel for engine 2. The liquefied natural gas includes methane, ethane, propane, etc. The liquefied natural gas is vaporized by a vaporizer (not shown). The vaporized natural gas passes through supply pipe 11 and is supplied to fuel injection unit 12.

[0016] The engine 2 is an internal combustion engine that generates power by burning and expanding a mixture of natural gas and intake air. The engine 2 has four cylinders 21. FIG. 2 is a diagram for explaining the configuration of the cylinders 21. The four cylinders 21 are provided in an engine block 23 of the engine 2.

[0017] An intake pipe 22 for supplying intake air to the cylinder 21 is connected to the cylinder 21. A fuel injection unit 12 is provided in the intake pipe 22. The fuel injection unit 12 injects natural gas that has passed through the supply pipe 11 into the intake pipe 22. When the natural gas is injected from the fuel injection unit 12 into the intake pipe 22, it is mixed with the intake air in the intake pipe 22. The mixture is supplied to the combustion chamber 6 of the cylinder 21.

[0018] Each cylinder 21 is provided with an ignition plug 3 and a piston 5. The spark plug 3 ignites the air-fuel mixture in the combustion chamber 6. The spark plug 3 ignites the air-fuel mixture in the combustion chamber 6 by electrically generating a spark.

[0019] The piston 5 slides inside the cylinder 21, drawing in and compressing the air-fuel mixture, and pushing the exhaust gas after the mixture has been burned out of the cylinder 21. The piston 5 draws the air-fuel mixture into the cylinder 21 as it descends from top dead center to bottom dead center (intake stroke). After descending to bottom dead center, the piston 5 compresses the mixture as it rises to top dead center (compression stroke). The compressed air-fuel mixture is ignited by the spark plug 3, causing the mixture to burn. The piston 5 is pushed down to bottom dead center by the expanding combustion gases (combustion stroke). Due to inertia and expansion in other cylinders 21, the piston 5 rises again to top dead center. When the piston 5 rises to top dead center, the exhaust valve opens, pushing the combustion gases out of the cylinder 21 (exhaust stroke).

[0020] During the combustion process, pressure increases due to the expansion of the combustion gas, generating a pressure wave within the combustion chamber 6. The pressure wave reverses when it hits the top surface of the piston 5 or the cylinder 21, and so travels back and forth within the combustion chamber 6. As the pressure wave travels back and forth in the sliding direction of the piston 5, the cylinder 21 vibrates in the sliding direction of the piston 5. The vibration in the sliding direction increases as combustion progresses within the combustion chamber 6. Therefore, the acceleration of the vibration of the cylinder 21 in the sliding direction reaches a maximum when the pressure of the combustion gas reaches a maximum. In this way, there is a correlation between the combustion state within the combustion chamber 6 and the acceleration of the vibration of the cylinder 21 in the sliding direction, and this acceleration can be said to be a characteristic quantity that indicates the combustion state within the combustion chamber 6.

[0021] The sensor 4 detects the vibration of the cylinder 21 as a characteristic quantity indicating the combustion state. Specifically, the sensor 4 is an acceleration sensor that detects the acceleration of the vibration of the cylinder 21 in the sliding direction of the piston 5 as a characteristic quantity. The sensor 4 detects the acceleration at a predetermined interval and outputs the detected acceleration to the ignition control device 7. The predetermined interval is, for example, 1 millisecond or less, but is not limited to this.

[0022] The sensor 4 is provided in the cylinder head 24. Specifically, the sensor 4 is provided near the intake system of the cylinder head 24 (for example, within a predetermined range including the intake pipe 22). However, the sensor 4 is not limited to this, and may be provided anywhere in the cylinder head 24 as long as it can detect the acceleration of vibration of the cylinder 21 in the sliding direction of the piston 5. The sensor 4 detects the acceleration of vibration of one or more of the four cylinders 21 in the sliding direction of the piston 5. In this embodiment, four sensors 4 are provided so that the acceleration of vibration of each cylinder 21 in the sliding direction of the piston 5 can be detected. Note that the number of sensors 4 does not need to be four, as long as one or more sensors are provided. For example, only two sensors may be provided so that the acceleration of vibration of two of the four cylinders 21 in the sliding direction can be detected.

[0023] FIG. 3 is a diagram illustrating the relationship between the combustion state and acceleration. The horizontal axis of FIG. 3 indicates the phase in the combustion cycle, and the vertical axis indicates the rate of increase in acceleration. Phase Q is the phase at which the air-fuel mixture is ignited. Phase Q is set at reference phase A so that combustion progresses rapidly within combustion chamber 6. Reference phase A is the phase at which the piston 5 of engine 2 is at top dead center during the combustion stroke.

[0024] Graph D1, shown by a solid line in Figure 3, is a graph showing the relationship between the phase and the rate of increase in acceleration in the combustion cycle of natural gas before the ratio of its components changes. Graph D1 shows that the rate of increase in acceleration is greatest at reference phase A, where the piston 5 is at top dead center. In other words, when the mixture of natural gas and intake air before the ratio of its components changes is ignited at phase Q, combustion progresses rapidly at the timing of reference phase A.

[0025] Incidentally, the temperature of the liquefied natural gas stored in the container 1 rises due to the inflow of heat from outside the container 1. As the temperature of the liquefied natural gas rises, methane, which has a low boiling point, vaporizes first, and the ratio of its components changes. Specifically, as the temperature of the liquefied natural gas rises, the ratio of methane decreases and the ratios of ethane and propane increase. In this case, the mixture becomes more flammable.

[0026] Graph D2, shown by the dashed line, is a graph showing the relationship between the phase and the rate of increase in acceleration in the natural gas combustion cycle after a change in the proportions of the components. Graph D2 shows that the rate of increase in acceleration reaches its maximum before reference phase A is reached. In other words, if the mixture of natural gas and intake air after a change in the proportions of the components is ignited at phase Q, combustion progresses rapidly before reference phase A is reached. Thus, if the mixture is ignited at the same ignition timing as before the change in the proportions of the components of liquefied natural gas when the proportions of the components have changed, the mixture cannot be burned properly.

[0027] Therefore, if the maximum value of the rate of increase in acceleration occurs before reference phase A, the ignition control device 7 delays the ignition timing from phase Q to phase Q1 so that the maximum value of the rate of increase in acceleration occurs at reference phase A. Graph D3, indicated by a dotted line in FIG. 3, is a graph showing the relationship between the phase and the rate of increase in acceleration when the mixture of natural gas and intake air after the component ratio has changed is ignited at phase Q1. Graph D3, like graph D1, shows that the rate of increase in acceleration is maximized at reference phase A, when the piston 5 reaches top dead center. In other words, when the mixture of natural gas and intake air after the component ratio has changed is ignited at phase Q1, combustion progresses rapidly at reference phase A.

[0028] In this way, when the ratio of the components of the liquefied natural gas changes, the ignition control device 7 can appropriately change the ignition timing to appropriately combust the mixture. The configuration of the ignition control device 7 will be described below.

[0029] [Configuration of ignition control device 7] 4 is a diagram illustrating the configuration of the ignition control device 7. The ignition control device 7 has a storage unit 71 and a control unit 72. The storage unit 71 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The storage unit 71 stores a program executed by the control unit 72.

[0030] The control unit 72 is a computational resource including a processor such as a CPU (Central Processing Unit). The control unit 72 executes a program stored in the storage unit 71 to realize functions as an acquisition unit 721, an identification unit 722, and an ignition control unit 723.

[0031] The acquisition unit 721 acquires the acceleration of vibration of the cylinder 21 in the sliding direction of the piston 5 from the sensor 4. The acquisition unit 721 acquires the acceleration detected by each sensor 4 in association with the phase in the combustion cycle of the engine 2 corresponding to the acceleration. Specifically, the acquisition unit 721 acquires the acceleration in association with the phase at the time the acceleration was detected for each cylinder 21.

[0032] The identification unit 722 identifies the maximum phase at which the rate of increase in acceleration is maximized. For example, the identification unit 722 identifies, for each cylinder 21, the maximum phase at which the rate of increase in acceleration is maximized based on multiple accelerations detected during one combustion cycle and phases associated with each acceleration. Specifically, the identification unit 722 identifies the maximum phase at which the rate of increase in acceleration is maximized by analyzing a data sequence in which accelerations corresponding to phases are arranged in ascending order. More specifically, the identification unit 722 identifies, as the maximum phase, the phase at which the difference between the acceleration corresponding to one phase and the acceleration corresponding to the phase next to the one phase is maximized. Note that the identification unit 722 is not limited to the above, and may identify the maximum phase at which the rate of increase in acceleration is maximized by differentiating the acceleration with respect to the phase.

[0033] The ignition control unit 723 controls the ignition timing of the air-fuel mixture. For example, if the maximum phase deviates significantly from the reference phase A, knocking or incomplete combustion of the air-fuel mixture may occur. Therefore, the ignition control unit 723 changes the ignition timing of the cylinder 21 whose maximum phase differs from the reference phase A among the multiple cylinders 21. Specifically, the ignition control unit 723 changes the ignition timing of the cylinder 21 whose maximum phase is outside a predetermined range including the reference phase A. The predetermined range is defined as a timing range in which knocking or incomplete combustion does not occur as the timing of combustion in the combustion chamber. For example, the predetermined range is equal to or greater than a lower limit A1 that is smaller than the reference phase A and equal to or less than an upper limit A2 that is larger than the reference phase A. The lower limit A1 and the upper limit A2 may be determined appropriately through experiments or the like. For example, the predetermined range is specifically defined as a range of plus or minus 3 degrees centered on the reference phase A.

[0034] To determine whether or not the ignition timing needs to be changed, the ignition control unit 723 determines for each cylinder 21 whether the maximum phase is within a predetermined range. If the maximum phase is within the predetermined range, the ignition control unit 723 determines that there is no need to change the ignition timing because there is little risk of knocking or incomplete combustion occurring. In this case, the ignition control unit 723 does not change the ignition timing.

[0035] If the maximum phase is outside a predetermined range, knocking or incomplete combustion may occur, and therefore the ignition control unit 723 changes the ignition timing of the air-fuel mixture. For example, if the maximum phase is earlier than the predetermined range, knocking may occur, and therefore the ignition control unit 723 delays the ignition timing so that the maximum phase falls within the predetermined range. Specifically, the ignition control unit 723 delays the ignition timing by a predetermined phase. The predetermined phase is, for example, 1 degree, but is not limited to this.

[0036] The ignition control unit 723 retards the ignition timing by a predetermined phase and determines whether the maximum phase of the combustion cycle after retarding the ignition timing by the predetermined phase is outside a predetermined range. The ignition control unit 723 retards the ignition timing by the predetermined phase until the maximum phase falls within the predetermined range, and determines whether the maximum phase is within the predetermined range each time the ignition timing is retarded by the predetermined phase. In this way, the ignition control unit 723 can keep the maximum phase within the predetermined range, thereby suppressing the occurrence of knocking and properly combusting the air-fuel mixture.

[0037] The ignition control unit 723 may change the ignition timing to bring the maximum phase within a predetermined range, and then change the ignition timing so that the difference between the maximum phase and reference phase A becomes smaller. The ignition control unit 723 changes the ignition timing so that the maximum phase falls within a reference range that is narrower than the predetermined range. Specifically, the reference range is a range of ±1 degree centered around reference phase A. The ignition control unit 723 delays the ignition timing if the maximum phase is before the reference range, and advances the ignition timing if the maximum phase is after the reference range. In this way, the ignition control unit 723 can match the maximum phase with reference phase A by reducing the difference between the maximum phase and reference phase A.

[0038] In this way, when the air-fuel mixture becomes more combustible due to an increase in the proportion of ethane or propane, the ignition control unit 723 can delay the ignition timing of the air-fuel mixture and set the maximum phase to the reference phase A. As a result, the air-fuel mixture begins to burn rapidly at an appropriate phase when the piston 5 reaches top dead center.

[0039] If the maximum phase is later than the predetermined range, there is a risk of incomplete combustion of the air-fuel mixture, so the ignition control unit 723 advances the ignition timing by a predetermined phase so that the maximum phase falls within the predetermined range. The ignition control unit 723 determines whether the maximum phase of the combustion cycle after advancing the ignition timing by the predetermined phase is within the predetermined range. If the maximum phase is outside the predetermined range, the ignition control unit 723 advances the ignition timing by the predetermined phase until the maximum phase falls within the predetermined range, and each time the ignition timing is advanced by the predetermined phase, it determines whether the maximum phase is within the predetermined range.

[0040] As a result, when the proportion of methane increases due to the addition of liquefied natural gas, making the air-fuel mixture difficult to burn, the ignition control unit 723 can advance the ignition timing of the air-fuel mixture to bring the maximum phase within a predetermined range. In this way, the ignition control unit 723 can suppress incomplete combustion of the air-fuel mixture and properly burn the mixture.

[0041] [Processing to change ignition timing] 5 is a flowchart showing an example of a process for changing the ignition timing. The process for changing the ignition timing is executed while the engine 2 is operating.

[0042] The acquisition unit 721 acquires acceleration and phase (step S1). Specifically, the acquisition unit 721 acquires the acceleration of vibration of the cylinder 21 in the sliding direction of the piston 5 detected by the sensor 4 and the phase at which the acceleration was detected, in association with each other. The acquisition unit 721 acquires the acceleration and phase for each cylinder 21, in association with each other.

[0043] The determination unit 722 determines whether the acceleration and phase have been acquired in one combustion cycle (step S2). If the acceleration and phase have not been acquired in one combustion cycle (No in step S2), the determination unit 722 waits until the acceleration and phase are acquired in one combustion cycle.

[0044] When the acceleration and the phase are acquired in one combustion cycle (Yes in step S2), the identification unit 722 identifies the maximum phase (step S3). The maximum phase is the phase in which the rate of increase of the acceleration is maximum. The identification unit 722 associates the acceleration and the phase in one combustion cycle and identifies the maximum phase by analyzing a data string arranged in ascending order of phase.

[0045] The ignition control unit 723 determines whether the maximum phase is outside a predetermined range (step S4). If the maximum phase is within the predetermined range (No in step S4), the ignition control unit 723 returns to step S1. If the maximum phase is outside the predetermined range (Yes in step S4), the ignition control unit 723 determines whether the maximum phase is before the predetermined range (step S5).

[0046] If the maximum phase is earlier than the predetermined range (Yes in step S5), the ignition control unit 723 delays the ignition timing (step S6). Specifically, the ignition control unit 723 delays the ignition timing by a predetermined phase from the current ignition timing. The predetermined phase is, for example, 1 degree, but is not limited to this. After delaying the ignition timing by the predetermined phase, the ignition control unit 723 returns to step S1.

[0047] If the maximum phase is later than the predetermined range (No in step S5), the ignition control unit 723 advances the ignition timing (step S7). Specifically, the ignition control unit 723 advances the ignition timing by a predetermined phase from the current ignition timing. After advancing the ignition timing by the predetermined phase, the ignition control unit 723 returns to step S1.

[0048] [Effects of Control System S] When external heat flows into the container 1 storing liquefied natural gas, methane boil-off gas is generated. As a result, the proportion of methane in the liquefied natural gas decreases, while the proportions of ethane and propane increase. The increase in the proportion of ethane and propane makes the mixture of natural gas and intake air more combustible. In this case, if the mixture is ignited at the same timing as when the proportion of ethane and propane in the liquefied natural gas has not increased, combustion will proceed rapidly before the desired phase of the combustion cycle is reached.

[0049] As described in this embodiment, the control system S first acquires a feature quantity indicating the actual combustion state in the combustion chamber 6 in association with a combustion cycle phase corresponding to the feature quantity. Next, the control system S identifies the maximum phase at which the rate of increase of the feature quantity is greatest, based on the feature quantity indicating the actual combustion state and the phase associated with the feature quantity. If the identified maximum phase is outside a predetermined range set as the timing for combustion, the control system S changes the ignition timing so that the maximum phase falls within the predetermined range. This allows the control system S to properly combust the air-fuel mixture even if the ratio of components changes due to the generation of methane boil-off gas in a container that stores liquefied natural gas.

[0050] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0051] S Control System 1 container 2 engines 3 Spark plugs 4 sensors 5 pistons 6 Combustion chamber 11 Supply pipeline 12 Fuel injection part 21 cylinders 22 Intake pipe 23 Engine block 24 Cylinder head 7 Ignition control device 71 Memory section 72 Control Unit 721 Acquisition Department 722 Specific part 723 Ignition control unit

Claims

1. a sensor provided in an engine using a mixture of intake air and vaporized liquefied natural gas containing methane, the sensor detecting a characteristic quantity indicating a combustion state in a combustion chamber of the engine at predetermined intervals; an acquisition unit that acquires the feature amount detected by the sensor and a phase in a combustion cycle of the engine corresponding to the feature amount in association with each other; an identification unit that identifies a maximum phase corresponding to a maximum value of an increase rate of the feature amounts based on the plurality of feature amounts detected during one of the combustion cycles and the phases associated with each of the feature amounts; an ignition control unit that, when the maximum phase is outside a predetermined range set as a timing for causing combustion in the combustion chamber, changes an ignition timing of the air-fuel mixture so that the maximum phase falls within the predetermined range; A control system having:

2. the sensor is an acceleration sensor that detects, as the characteristic amount, an acceleration of vibration of the cylinder in a sliding direction of a piston that slides inside the cylinder of the engine; the specifying unit specifies the maximum phase at which the rate of increase of the acceleration becomes a maximum value. The control system of claim 1 .

3. a plurality of the sensors corresponding to each of the plurality of cylinders of the engine; each of the plurality of sensors detects the acceleration of vibration in the sliding direction of the corresponding cylinder; the acquisition unit acquires the acceleration and the phase corresponding to the acceleration of each of the plurality of cylinders from each sensor; the specifying unit specifies the maximum phase for each cylinder, The ignition control unit changes the ignition timing of a cylinder whose maximum phase is outside the predetermined range. The control system of claim 2 .

4. the predetermined range is a range including a reference phase at which the piston of the engine is positioned at top dead center in the combustion stroke of the combustion cycle. The control system of claim 1 .

5. the ignition control unit delays the ignition timing when the maximum phase is earlier than the predetermined range, and advances the ignition timing when the maximum phase is later than the predetermined range. The control system of claim 4.

6. the ignition control unit changes the ignition timing so that the maximum value of the increase rate of the characteristic amount coincides with the reference phase. The control system of claim 4.

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