JP2012017695A - Gas engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in fuel economy by suppressing sucking of a fuel gas supplied to a sub chamber into a main chamber in an unburned state.SOLUTION: A control device 30 uses pressure difference between a sub chamber pressure and a fuel passage pressure to calculate an upper limit crank angle (-130°) obtained by converting a timing of limitation until which a check valve 21 can remain opened into a crank angle. The control device 30 further calculates a valve open time of an injector 22 required for supplying a natural gas of a required fuel amount into the sub chamber 19 and calculates a valve open starting crank angle (-200°) of the injector 22 obtained by subtracting a crank angle (70°) corresponding to the valve open time of the injector 22 from the upper limit crank angle. The control device 30 controls valve open starting time of the injector 22 based on the valve open starting crank angle and delays the valve open starting time of the injector 22 as much as possible while the check valve 21 is in a valve open state.

Description

  The present invention relates to a gas engine including a main chamber to which a lean air-fuel mixture of fuel gas and air is supplied, and a sub chamber which is connected to the main chamber via an injection hole and to which fuel gas is supplied.

  Some gas engines include a main chamber to which a lean mixture of fuel gas and air is supplied, and a sub chamber that is in communication with the main chamber via an injection hole and to which fuel gas is supplied. . And the gas supply system for supplying fuel gas to each of these main chambers and subchambers is indicated by patent documents 1, for example.

  A gas fuel supply type internal combustion engine (gas engine) provided with the gas supply system of Patent Document 1 burns through a combustion part (main chamber) provided above a piston in a cylinder and an orifice (injection hole). And a pre-combustion part (sub chamber) communicating with the part. The pre-combustion unit is provided with an ignition source such as a spark plug for igniting gaseous fuel (fuel gas) in the pre-combustion unit.

  The gas supply system includes gas fuel supply means. The gas fuel supply means supplies the gaseous fuel to the first gas supply line for supplying gaseous fuel to the pre-combustion unit, the second gas supply line for supplying gaseous fuel to the combustion unit, and the first and second gas supply lines. It has a gas injector. Further, the gas fuel supply means includes a gas flow valve (one-way valve) that controls the relative ratio of the gaseous fuel supplied by the first and second gas supply lines.

  The gas flow valve is opened when the pressure in the pre-combustion section is lower than the pressure in the first gas supply line. On the other hand, the gas flow valve is closed when the pressure in the pre-combustion part is higher than the pressure in the first gas supply line.

  According to the gas supply system, when in the intake stroke, gaseous fuel and air are supplied from the second gas supply line and the air supply means to the combustion unit, and at the same time, only the gaseous fuel is supplied from the first gas supply line. It is supplied to the pre-combustion section via a gas flow valve. Further, in the compression stroke, a part of the air-fuel mixture in the combustion part is sent to the pre-combustion part through the orifice, and the pre-combustion part ignites the gaseous fuel by the ignition source. In the pre-combustion section, the ratio of gaseous fuel to air is relatively high, so that ignition of the gaseous fuel can be easily achieved and a chemical reaction takes place in the passage from the pre-combustion section to the combustion section through the orifice and the mixture Is ignited in the combustion section.

JP 7-700395 Gazette

  However, in the gas supply system of Patent Document 1, the gas flow valve opens immediately after the intake stroke is started, and therefore, from the first gas supply line through the gas flow valve immediately after the intake stroke is started. Gaseous fuel will be supplied to a precombustion part. For this reason, immediately after the start of the intake stroke, the gaseous fuel supplied to the pre-combustion part is sucked into the combustion part through the orifice without being burned, resulting in deterioration of fuel consumption.

  In the exhaust stroke, when the pressure in the combustion section becomes a relatively low exhaust pressure corresponding to the pressure in the exhaust passage due to exhaust pulsation, the pressure in the pre-combustion section becomes lower than the pressure in the first gas supply line. The gas flow valve may open. Then, gaseous fuel is sucked into the pre-combustion part through the gas flow valve from the first gas supply line, and is directly discharged from the combustion part to the exhaust passage through the orifice, causing deterioration of fuel consumption. .

  The present invention has been made in view of such circumstances, and its object is to prevent fuel gas supplied to the sub chamber from being sucked into the main chamber without being burned, thereby preventing deterioration of fuel consumption. It is to provide a gas engine that can.

  In order to achieve the above object, the invention according to claim 1 is directed to a main chamber facing a piston, a sub chamber communicating with the main chamber via an injection hole, and a fuel passage for guiding fuel gas to the sub chamber. And a fuel supply valve that is provided in the fuel passage and supplies fuel gas to the sub chamber, and is provided downstream of the fuel supply valve in the fuel passage and is based on a pressure difference between the sub chamber and the fuel passage. A check valve that allows the fuel gas to be supplied to the sub chamber by opening the valve, a sub chamber pressure estimating means that estimates the pressure of the sub chamber, and a pressure estimated by the sub chamber pressure estimating means And an upper limit crank angle calculating means for calculating an upper limit crank angle corresponding to the most retarded side in the opening range of the check valve, and a required fuel for calculating a required fuel amount of the fuel gas to be supplied to the sub chamber. Amount calculation means and the required fuel amount calculation A valve opening time calculating means for calculating a valve opening time of the fuel supply valve required to supply the required fuel amount using the required fuel amount calculated by the stage and the pressure in the sub chamber; and the valve opening time. Valve opening start crank angle calculating means for calculating the valve opening start crank angle of the fuel supply valve using the valve opening time calculated by the calculating means and the upper limit crank angle, and the valve opening start crank angle based on the valve opening start crank angle The gist of the invention is that it includes a valve opening start timing control means for controlling the valve opening start timing of the fuel supply valve.

  According to the present invention, the upper limit crank angle calculation means calculates the upper limit crank angle by converting the limit timing at which the check valve is opened into the crank angle using the pressure in the sub chamber. Further, the valve opening start crank angle calculating means opens the fuel supply valve by subtracting a crank angle corresponding to the valve opening time calculated by the valve opening time calculating means from the upper limit crank angle calculated by the upper limit crank angle calculating means. Calculate the valve start crank angle. Then, the valve opening start timing control means controls the valve opening start timing of the fuel supply valve based on the valve opening start crank angle, so that the fuel supply valve can be opened while the check valve is open. The start time is delayed as much as possible. Therefore, since the fuel supply valve does not open immediately after the intake stroke is started, for example, when the fuel supply valve is opened immediately after the intake stroke is started and fuel gas is supplied to the sub chamber. Since the fuel gas supplied into the sub chamber is not sucked into the main chamber through the nozzle hole without being burned by the lowering of the piston, the fuel consumption can be prevented from deteriorating.

  Further, in the exhaust stroke, when the pressure in the main chamber becomes a relatively low exhaust pressure corresponding to the pressure in the exhaust passage due to exhaust pulsation, the pressure in the sub chamber becomes lower than the pressure in the fuel passage, so The valve may open. However, since the valve opening start timing control means controls the valve opening start timing of the fuel supply valve based on the calculated valve opening start crank angle, even if the check valve is opened due to exhaust pulsation, The fuel gas is not unnecessarily supplied to the sub chamber. Therefore, the fuel gas is sucked into the sub chamber and is not directly discharged from the main chamber to the exhaust passage through the nozzle hole, so that the fuel consumption can be prevented from deteriorating.

Further, the sub chamber pressure estimation means may estimate the sub chamber pressure using a sub chamber pressure calculation map in which the sub chamber pressure is related to the engine speed and the intake pressure.
Further, the upper limit crank angle calculating means may calculate the upper limit crank angle using an upper limit crank angle calculation map in which a crank angle is related to a pressure difference between the sub chamber and the fuel passage.

Further, the required fuel amount calculating means may calculate the required fuel amount using a required fuel amount calculation map in which the required fuel amount is related to the engine speed and the intake pressure.
Further, the valve opening time calculating means opens the fuel supply valve using a characteristic line indicating a relationship between the valve opening time and the flow rate of the fuel supply valve according to a pressure difference between the sub chamber and the fuel passage. The valve time may be calculated.

  According to this invention, it is possible to prevent the fuel gas supplied to the sub chamber from being sucked into the main chamber without being burned, and to prevent deterioration in fuel consumption.

(A) is a schematic diagram which shows the whole structure about the gas engine and its control apparatus in embodiment, (b) is a graph which shows the relationship between a crank angle, a subchamber pressure, and fuel passage pressure. The graph which shows the characteristic line which linked the valve opening time and flow volume of the injector. The flowchart which shows the process sequence for a control apparatus to control the valve opening start time of an injector.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1A, the gas engine 10 includes a plurality of cylinders 11 (only one is shown in FIG. 1). A piston 12 is accommodated in each cylinder 11 so as to be able to reciprocate, and a main chamber 13 is defined by a top surface of the piston 12, an inner wall surface of the cylinder 11, and the like. Each cylinder 11 is connected to an intake passage 14 for sucking a lean air-fuel mixture into the main chamber 13 and an exhaust passage 15 for exhausting combustion gas from the main chamber 13. The portion of the intake passage 14 that opens to the main chamber 13 is opened and closed by the intake valve 16, and the portion of the exhaust passage 15 that opens to the main chamber 13 is opened and closed by the exhaust valve 17. An intake pressure sensor 32 is provided on the intake passage 14.

  In the gas engine 10, a sub chamber 19 communicating with the main chamber 13 through the nozzle hole 18 is provided above the main chamber 13. Further, the auxiliary chamber 19 is provided with an ignition plug 24, and the ignition plug 24 is provided so that its ignition point 24 a is located in the auxiliary chamber 19. Further, a fuel passage 20 is connected to the sub chamber 19, and an injector 22 as a fuel supply valve for supplying natural gas as fuel gas to the sub chamber 19 is provided in the fuel passage 20. The injector 22 is connected to the fuel tank 23 via a fuel pipe 23a, and natural gas stored in the fuel tank 23 is supplied to the injector 22. Natural gas adjusted to a constant pressure is injected from the injector 22, and the pressure of the fuel passage 20 (hereinafter referred to as “fuel passage pressure”) is injected by the injector 22, the sub chamber 19. Fluctuates due to fuel spills.

  The fuel passage 20 is provided with a check valve 21. The check valve 21 includes a spring 21a having a predetermined spring set pressure, and the fuel passage 20 is closed by bringing the valve body 21b such as a ball into contact with the valve seat by the biasing force of the spring 21a. When the pressure difference between the sub chamber 19 and the fuel passage 20 becomes equal to or higher than the spring set pressure due to a decrease in the pressure of the sub chamber 19 (hereinafter simply referred to as “sub chamber pressure”), the check valve 21 Pressure is applied in a direction against the urging force, and the valve body 21b is separated from the valve seat to be opened, allowing the supply of natural gas to the sub chamber 19. On the other hand, when the pressure difference between the sub chamber 19 and the fuel passage 20 becomes smaller than the spring set pressure, the check valve 21 is closed by the valve body 21b seated on the valve seat by the biasing force of the spring 21a. That is, when the sum of the sub chamber pressure and the spring set pressure becomes equal to the fuel passage pressure, the check valve 21 changes from the open state to the closed state.

  The gas engine 10 includes a control device 30 that controls the engine. The control device 30 includes a central processing control device (CPU), a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like.

  A crank angle detector 31 and an intake pressure sensor 32 are signal-connected to the control device 30. The crank angle detector 31 detects a rotation angle (crank angle) of a crankshaft (not shown) provided in the gas engine 10. Information on the crank angle detected by the crank angle detector 31 is sent to the control device 30. The control device 30 uses the crank angle information detected by the crank angle detector 31 to calculate the engine speed. The intake pressure sensor 32 detects the intake pressure in the intake passage 14. Information on the intake pressure detected by the intake pressure sensor 32 is sent to the control device 30.

  The control device 30 estimates the sub chamber pressure using the engine speed and the intake pressure. In the ROM, a sub chamber pressure calculation map in which the sub chamber pressure is related to the engine speed and the intake pressure is stored in advance. Therefore, the control device 30 in the present embodiment has a function as a sub chamber pressure estimating means for estimating the pressure of the sub chamber 19. Further, the control device 30 adjusts the injection pressure of the injector 22 and controls the injector 22 so that natural gas is injected from the injector 22 at a constant pressure. Then, the control device 30 estimates the fuel passage pressure using the injection pressure of the injector 22.

  Further, the control device 30 calculates the upper limit crank angle corresponding to the most retarded side in the valve opening range of the check valve 21 using the pressure difference between the sub chamber pressure and the fuel passage pressure. Here, the “upper crank angle” means that the sum of the sub chamber pressure and the spring set pressure is equal to the fuel passage pressure after the check valve 21 is opened due to the start of the intake stroke. The crank angle when the stop valve 21 changes from the open state to the closed state. That is, the upper limit crank angle is a crank angle when the pressure difference between the sub chamber pressure and the fuel passage pressure becomes equal to the spring set pressure. Note that the upper limit crank angle varies as the sub-chamber pressure varies with the engine load.

  This upper limit crank angle is obtained in advance based on the values of the sub chamber pressure and the fuel passage pressure obtained by experiments, and the ROM has a crank angle with respect to the pressure difference between the sub chamber pressure and the fuel passage pressure. Are stored in advance. Therefore, the control device 30 in the present embodiment also has a function as an upper limit crank angle calculation unit that calculates the upper limit crank angle corresponding to the most retarded side in the valve opening range of the check valve 21.

  Further, the control device 30 calculates the required fuel amount of natural gas to be supplied into the sub chamber 19 using the engine speed and the intake pressure. In the ROM, a required fuel amount calculation map in which the required fuel amount is related to the engine speed and the intake pressure is stored in advance. Therefore, the control device 30 in the present embodiment also has a function as a required fuel amount calculating means for calculating the required fuel amount of natural gas to be supplied into the sub chamber 19.

  The control device 30 calculates the valve opening time of the injector 22 required for supplying the required fuel amount to the sub chamber 19 using the calculated required fuel amount, sub chamber pressure, and fuel passage pressure. This valve opening time is the length of time from when the injector 22 opens until it closes. The valve opening time of the injector 22 is calculated using a characteristic line that relates the valve opening time of the injector 22 and the flow rate. The characteristic line is shown in FIG. In FIG. 2, the horizontal axis indicates the valve opening time of the injector 22, and the vertical axis indicates the flow rate of the injector 22.

  In addition, the slope of this characteristic line changes as the sub-chamber pressure varies with the engine load, that is, the pressure difference between the sub-chamber pressure and the fuel passage pressure varies. FIG. 2 shows characteristic lines when the subchamber pressure α and the subchamber pressure β. The subchamber pressure α is assumed to be higher than the subchamber pressure β. A characteristic line at the sub-chamber pressure α is indicated by a solid line Y1, and a characteristic line at the sub-chamber pressure β is indicated by a two-dot chain line Y2. Here, since the pressure of the fuel injected from the injector 22 is substantially constant, the pressure difference from the fuel passage pressure at the sub chamber pressure β is greater than the pressure difference from the fuel passage pressure at the sub chamber pressure α. Is also getting bigger.

  As shown in FIG. 2, when the required fuel amount is constant, if the pressure difference between the sub chamber pressure and the fuel passage pressure is large as in the case of the sub chamber pressure β, natural gas is sucked into the sub chamber 19 vigorously. Therefore, the valve opening time of the injector 22 is shortened. On the other hand, if the pressure difference between the sub chamber pressure and the fuel passage pressure is small as in the case of the sub chamber pressure α, the natural gas is slowly sucked into the sub chamber 19 and therefore the valve opening time of the injector 22 becomes long. . The characteristic line in FIG. 2 is obtained in advance by experiment, and the ROM shows the characteristic indicating the relationship between the valve opening time and the flow rate of the injector 22 according to the pressure difference between the sub chamber pressure and the fuel passage pressure. A plurality of lines are stored in addition to Y1 and Y2. Therefore, the control device 30 in the present embodiment also has a function as valve opening time calculation means for calculating the valve opening time of the injector 22. In addition, the control device 30 converts the calculated valve opening time of the injector 22 into a crank angle.

  Further, the control device 30 calculates the valve opening start crank angle of the injector 22 from the engine speed and the valve opening time of the injector 22. The valve opening start crank angle is a crank angle value obtained by subtracting the crank angle corresponding to the valve opening time of the injector 22 from the upper limit crank angle. Therefore, the control device 30 in the present embodiment also has a function as a valve opening start crank angle calculation unit of the injector 22.

  Then, the control device 30 controls the valve opening start timing of the injector 22 based on the calculated valve opening start crank angle. Therefore, the control device 30 in this embodiment also has a function as valve opening start timing control means for controlling the valve opening start timing of the injector 22.

Next, a processing procedure for the control device 30 of the present embodiment to control the valve opening start timing of the injector 22 will be described.
As shown in FIG. 3, first, the control device 30 uses the engine speed calculated based on the information from the crank angle detector 31 and the intake pressure detected by the intake pressure sensor 32 to use the sub-chamber pressure. The sub chamber pressure is estimated from the calculation map (step S11). Next, the control device 30 calculates the upper limit crank angle from the upper limit crank angle calculation map based on the pressure difference between the sub chamber pressure and the fuel passage pressure estimated in step S11 (step S12).

  Next, the control device 30 uses the engine speed calculated based on the information from the crank angle detector 31 and the intake pressure detected by the intake pressure sensor 32 to calculate the sub chamber 19 from the required fuel amount calculation map. The required fuel amount of natural gas to be supplied is calculated (step S13). Next, the control device 30 calculates the valve opening time of the injector 22 from the characteristic line using the sub-chamber pressure, the fuel passage pressure, and the required fuel amount estimated in step S11 (step S14). For example, when the sub-chamber pressure is α, the valve opening time Tx of the injector 22 required to obtain the required fuel amount Fx is calculated using the characteristic line Y1 shown in FIG.

  Next, the control device 30 calculates the valve opening start crank angle of the injector 22 using the engine speed and the valve opening time of the injector 22 (step S15). The valve opening start crank angle calculated in step S15 is a crank angle (in this embodiment) corresponding to the valve opening time of the injector 22 from the upper limit crank angle (in the present embodiment, crank angle −130 °) calculated in step S12. The crank angle (crank angle 70 °) is subtracted (in this embodiment, the crank angle is −200 °). Next, the control device 30 controls the valve opening start timing of the injector 22 based on the valve opening start crank angle calculated in step S15 (step S16).

Next, the operation of the gas engine 10 will be described.
FIG. 1B is a graph showing a change in sub-chamber pressure in one cycle at a certain engine load and a change in pressure obtained by subtracting the spring set pressure from the fuel passage pressure. The abscissa indicates the crank angle, and the ordinate indicates the pressure. Further, the change in the sub chamber pressure is indicated by a solid line L1, and the change in the pressure obtained by subtracting the spring set pressure from the fuel passage pressure is indicated by a one-dot chain line L2. Moreover, the control apparatus 30 performs the process of said step S11-step S16 for every cycle. The control device 30 calculates the upper limit crank angle (−130 °), the crank angle (70 °) corresponding to the valve opening time of the injector 22, and the valve opening start crank angle (−200 °) of the injector 22. To do.

  As shown in FIG. 1B, first, when the intake valve 16 is opened, the piston 12 descends from the top dead center toward the bottom dead center, and natural gas and air enter the main chamber 13 from the intake passage 14. The intake valve 16 is closed while the piston 12 reaches the bottom dead center and rises from the bottom dead center toward the top dead center (intake stroke).

  In this intake stroke, when the piston 12 descends from the top dead center toward the bottom dead center, the sub chamber pressure decreases, the pressure difference between the sub chamber pressure and the fuel passage pressure exceeds the spring set pressure, and the check valve 21 Is opened. At this time, the control device 30 issues a valve opening command to the injector 22 so that the injector 22 opens when the check valve 21 is in the valve open state when the valve opening start crank angle is −200 °. Then, natural gas is injected from the injector 22, and natural gas is supplied into the sub chamber 19.

  Next, the piston 12 rises toward top dead center, and the lean air-fuel mixture in the main chamber 13 is compressed (compression stroke). In this compression stroke, the lean air-fuel mixture in the main chamber 13 flows into the sub chamber 19 from the main chamber 13 through the nozzle hole 18, and the natural gas supplied into the sub chamber 19 during the intake stroke The lean air-fuel mixture is mixed, and the ratio of natural gas to air in the sub-chamber 19 is increased, and an air-fuel mixture corresponding to the theoretical air-fuel mixture is formed in the sub-chamber 19.

  Here, when the piston 12 rises from the bottom dead center toward the top dead center, the pressure in the sub chamber 19 rises, and the pressure difference between the sub chamber pressure and the fuel passage pressure becomes smaller than the spring set pressure, and vice versa. The stop valve 21 is closed. At this time, natural gas corresponding to the required fuel amount is supplied into the sub chamber 19. Then, the control device 30 sends a valve closing command to the injector 22 so that the injector 22 is closed, and the injection of natural gas from the injector 22 ends. Further, the closed state of the check valve 21 prevents the lean air-fuel mixture flowing from the main chamber 13 through the nozzle hole 18 into the sub chamber 19 from flowing into the fuel passage 20 side. .

  Then, the spark plug 24 is activated and spark ignition is performed in the sub chamber 19. The combustion gas in the sub chamber 19 burned by the spark ignition by the spark plug 24 is injected into the main chamber 13 as a flame jet, so that the lean air-fuel mixture in the main chamber 13 is ignited and burned.

  The combustion gas that has become high temperature and pressure due to the combustion of the lean mixture pushes the piston 12, and the piston 12 descends from the top dead center toward the bottom dead center (expansion stroke). Then, the exhaust valve 17 is opened, and the piston 12 rises from the bottom dead center toward the top dead center, whereby the piston 12 pushes the combustion gas in the main chamber 13 to the exhaust passage 15 (exhaust stroke). By repeating such one cycle, the piston 12 is reciprocated.

In the above embodiment, the following effects can be obtained.
(1) The control device 30 utilizes the pressure difference between the sub chamber pressure and the fuel passage pressure, and the upper limit crank angle (−130 °) obtained by converting the limit timing at which the check valve 21 is opened into the crank angle. Is calculated. Further, the control device 30 calculates the valve opening time of the injector 22 required for supplying the required amount of natural gas into the sub chamber 19 and also calculates the crank angle (70 corresponding to the valve opening time of the injector 22). The valve opening start crank angle (−200 °) of the injector 22 is calculated by subtracting (°) from the upper limit crank angle. Then, the control device 30 controls the valve opening start timing of the injector 22 based on the valve opening start crank angle, so that the valve opening start timing of the injector 22 can be performed while the check valve 21 is in the valve open state. Delayed as long as possible. Therefore, since the injector 22 does not open immediately after the intake stroke is started, for example, when the injector 22 opens and the natural gas is supplied to the sub chamber 19 immediately after the intake stroke is started, As the piston 12 descends, the natural gas supplied into the sub chamber 19 is not sucked into the main chamber 13 through the nozzle hole 18 without being burned. As a result, fuel consumption can be prevented from deteriorating.

  (2) In the exhaust stroke, when the pressure in the main chamber 13 becomes a relatively low exhaust pressure corresponding to the pressure in the exhaust passage 15 due to exhaust pulsation, the pressure in the sub chamber 19 is changed to the pressure in the fuel passage 20. The check valve 21 may open. However, since the control device 30 controls the valve opening start timing of the injector 22 based on the calculated valve opening start crank angle, even if the check valve 21 is opened due to the pulsation of the exhaust gas, natural gas is not generated. It is not unnecessarily supplied to the sub chamber 19. Therefore, natural gas is sucked into the sub chamber 19 and is not directly discharged from the main chamber 13 to the exhaust passage 15 through the nozzle hole 18 as it is, so that deterioration of fuel consumption can be prevented.

  (3) In this embodiment, natural gas is supplied from the injector 22 to the sub chamber 19 via the fuel passage 20 and the check valve 21. Therefore, even if the space around the sub chamber 19 is narrow, the natural gas can be efficiently supplied to the sub chamber 19. Further, since the injector 22 is not directly exposed to the sub chamber 19, deterioration of the injector 22 due to the flame generated in the sub chamber 19 can be prevented.

In addition, you may change the said embodiment as follows.
In the embodiment, the control device 30 estimates the sub-chamber pressure using the engine speed and the intake pressure. However, the control device 30 is not limited to this, and for example, the sub-chamber is used using the engine speed and the throttle opening. The pressure may be estimated.

  In the embodiment, the control device 30 calculates the required fuel amount of the natural gas to be supplied into the sub chamber 19 using the engine speed and the intake pressure. The required fuel amount may be calculated using the number and the throttle opening.

In the embodiment, natural gas is applied as the fuel gas. However, the present invention is not limited to this. For example, LPG (liquefied petroleum gas) may be applied as the fuel gas.
In the embodiment, the control device 30 estimates the fuel passage pressure using the injection pressure of the injector 22, and calculates the upper limit crank angle from the pressure difference between the estimated fuel passage pressure and the sub chamber pressure. Not limited to. Since the area of the fuel passage 20 on the downstream side of the injector 22 is considerably smaller than the area of the sub chamber 19 and the injection pressure of the injector 22 is constant, the fluctuation of the fuel passage pressure is larger than the fluctuation of the sub chamber pressure. Pretty small. Therefore, the control device 30 may calculate the upper limit crank angle using only the sub chamber pressure. In this case, the upper limit crank angle is obtained in advance based on the value of the sub chamber pressure obtained by experiments, and the upper limit crank angle calculation map in which the upper limit crank angle is related to the sub chamber pressure is stored in the ROM. Is stored in advance.

Next, the technical idea that can be grasped from the above embodiment and other examples will be described below.
(A) The valve opening start crank angle calculating means calculates the valve opening start crank angle using an engine speed and a valve opening time of the fuel supply valve. The gas engine according to any one of the above.

  (B) The gas engine according to any one of claims 1 to 5 and the technical idea (a), wherein the fuel gas is natural gas.

  DESCRIPTION OF SYMBOLS 10 ... Gas engine, 12 ... Piston, 13 ... Main chamber, 18 ... Injection hole, 19 ... Sub chamber, 20 ... Fuel passage, 21 ... Check valve, 22 ... Injector as fuel supply valve, 30 ... Sub chamber pressure estimation A control device having functions as means, upper limit crank angle calculation means, required fuel amount calculation means, valve opening time calculation means, valve opening start crank angle calculation means, and valve opening start timing control means.

Claims (5)

A main chamber facing the piston,
A sub chamber communicating with the main chamber via a nozzle hole;
A fuel passage for guiding fuel gas to the sub chamber;
A fuel supply valve that is provided in the fuel passage and supplies fuel gas to the sub chamber;
A check valve that is provided downstream of the fuel supply valve in the fuel passage and opens based on a pressure difference between the sub chamber and the fuel passage to allow fuel gas to be supplied to the sub chamber;
Sub chamber pressure estimating means for estimating the pressure of the sub chamber;
Upper limit crank angle calculating means for calculating an upper limit crank angle corresponding to the most retarded side in the valve opening range of the check valve using the pressure estimated by the sub chamber pressure estimating means;
A required fuel amount calculating means for calculating a required fuel amount of fuel gas to be supplied into the sub chamber;
A valve opening time calculating means for calculating a valve opening time of the fuel supply valve required to supply the required fuel quantity by using the required fuel quantity calculated by the required fuel quantity calculating means and the pressure in the sub chamber; ,
Valve opening start crank angle calculating means for calculating the valve opening start crank angle of the fuel supply valve using the valve opening time calculated by the valve opening time calculating means and the upper limit crank angle;
A gas engine comprising: a valve opening start timing control means for controlling a valve opening start timing of the fuel supply valve based on the valve opening start crank angle.   2. The sub-chamber pressure estimating means estimates the sub-chamber pressure using a sub-chamber pressure calculation map in which the sub-chamber pressure is related to the engine speed and the intake pressure. The gas engine described in 1.   The upper limit crank angle calculation means calculates the upper limit crank angle using an upper limit crank angle calculation map in which a crank angle is related to a pressure difference between the sub chamber and the fuel passage. The gas engine according to claim 1 or 2.   The required fuel amount calculating means calculates the required fuel amount using a required fuel amount calculation map in which the required fuel amount is related to the engine speed and the intake pressure. 4. The gas engine according to any one of 3.   The valve opening time calculating means uses the characteristic line indicating the relationship between the valve opening time and the flow rate of the fuel supply valve according to the pressure difference between the sub chamber and the fuel passage to open the fuel supply valve. The gas engine according to claim 1, wherein the gas engine is calculated.

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