JP2016075235A - Control device and control method for ignition timing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device and control method for ignition timing, capable of suppressing occurrence of knocking even in a case where concentration of methane decreases.SOLUTION: A control device 50 controls ignition timing of an ignition plug at base ignition timing according to the operation state of an engine 5 and at target ignition timing based on a correction amount to the base ignition timing. The control device 50 calculates a suction air fuel ratio based on an air amount of air fuel mixture and a fuel amount of the air fuel mixture, and an exhaust air fuel ratio based on an oxygen concentration of exhaust gas. Then, the control device 50 delays the correction amount, when a ratio of the exhaust air fuel ratio and the suction air fuel ratio is a value different from an allowance, and the exhaust air fuel ratio is higher than the suction air fuel ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ignition timing control device and control method applied to an engine using natural gas as fuel.

  Conventionally, as in Patent Document 1, for example, a natural gas vehicle including an engine using natural gas as a fuel is known. In a natural gas vehicle, compressed natural gas is stored in a gas tank, and combustion of an air-fuel mixture is started by ignition, as in a gasoline engine.

JP 2008-157127 A

  CNG (Compressed Natural Gas), which is one of natural gas, contains methane as a main component, and other components include ethane, propane, normal butane, isobutane, and the like having a lower octane number than methane. Therefore, knocking is likely to occur when the concentration of methane in the fuel decreases.

  An object of the present invention is to provide an ignition timing control device and control method capable of suppressing the occurrence of knocking even when the concentration of methane decreases.

  An ignition timing control device that solves the above-described problem is an ignition timing control device that controls the ignition timing of an engine that uses natural gas as a fuel, the base ignition timing and the base ignition timing corresponding to the operating state of the engine. An ignition timing control unit for controlling the ignition timing of the spark plug to a target ignition timing based on a correction amount for correcting the intake air-fuel ratio, and an intake air-fuel ratio for calculating an intake air-fuel ratio based on the air amount of the mixture and the fuel amount of the mixture A calculation unit; an exhaust air / fuel ratio calculation unit that calculates an exhaust air / fuel ratio based on an oxygen concentration of the exhaust gas; and a correction amount update unit that updates the correction amount based on a ratio between the exhaust air / fuel ratio and the intake air / fuel ratio; The correction amount update unit compares the ratio with an allowable value that is a value of the ratio that is determined not to change the composition of the fuel, and the ratio is different from the allowable value. And said To retard the correction amount when the exhaust air-fuel ratio is higher than Kisora ratio.

  An ignition timing control method that solves the above problem is an ignition timing control method that controls the ignition timing of an engine that uses natural gas as a fuel, and the control device that controls the ignition timing is in an operating state of the engine. And controlling the ignition timing of the spark plug to the target ignition timing based on the base ignition timing in accordance with the correction amount for correcting the base ignition timing, and the intake air-fuel ratio based on the air amount of the mixture and the fuel amount of the mixture And the ratio of the exhaust air / fuel ratio based on the oxygen concentration of the exhaust gas and the ratio of the exhaust air / fuel ratio and the intake air / fuel ratio, and the ratio and the ratio at which the fuel composition is determined not to change When the ratio is different from the allowable value and the exhaust air / fuel ratio is higher than the intake air / fuel ratio, the correction amount is retarded.

  Methane, which is the main component of natural gas, has a larger theoretical air / fuel ratio than other components. Therefore, when the concentration of methane in the fuel increases, the amount of oxygen consumed during combustion increases even when the air amount and the fuel amount are the same, thereby lowering the exhaust air-fuel ratio. On the other hand, when the concentration of methane in the fuel decreases, the amount of oxygen consumed during combustion decreases and the exhaust air / fuel ratio increases.

  In the above configuration, the correction amount is retarded when the ratio and the allowable value are different values and the exhaust air / fuel ratio is higher than the intake air / fuel ratio. That is, the correction amount is retarded when it is determined that the exhaust air / fuel ratio is higher than the intake air / fuel ratio and the concentration of methane in the fuel has decreased. As a result, the target ignition timing is controlled to be retarded as compared to before the correction amount is updated. As a result, the occurrence of knocking can be suppressed even when the concentration of methane decreases.

In the ignition timing control apparatus, it is preferable that the correction amount update unit retards the correction amount as the exhaust air-fuel ratio is higher than the intake air-fuel ratio.
The lower the methane concentration, the higher the oxygen concentration in the exhaust gas and the higher the exhaust air / fuel ratio. As described above, the higher the exhaust air-fuel ratio, the greater the retardation of the correction amount, thereby suppressing the occurrence of knocking with a higher probability.

  In the ignition timing control device, the correction amount updating unit advances the correction amount before update when the correction amount before update advances the base ignition timing with respect to the ratio having the same value. When the angular amount is larger, the correction amount is delayed more greatly, and when the correction amount before update retards the base ignition timing, the correction amount is increased as the retardation amount by the correction amount before update is larger. It is preferable to retard the angle by a small amount.

  In other words, the correction amount that is updated based on the ratio is one of the indexes indicating the methane concentration of the fuel. As in the above configuration, by adjusting the retardation of the correction amount at the time of update in accordance with the correction amount before the update, an excessive decrease in engine output due to the retardation of the correction amount can be suppressed.

  In the ignition timing control apparatus, the correction amount update unit advances the correction amount when the ratio is different from the allowable value and the exhaust air-fuel ratio is lower than the intake air-fuel ratio. It is preferable.

  According to the above configuration, the correction amount is advanced when the ratio is a value different from the allowable value and the exhaust air-fuel ratio is lower than the intake air-fuel ratio. That is, the correction amount is advanced when it is determined that the exhaust air / fuel ratio is lower than the intake air / fuel ratio and the methane concentration has increased and knocking has become difficult to occur. Thereby, the output of the engine is increased while suppressing the occurrence of knocking.

It is a figure which shows schematic structure of the engine system carrying the ignition timing control apparatus of one Embodiment. (A) (b) (c) is a graph which shows an example of the relationship between a ratio and the update amount of a correction amount. It is a flowchart which shows an example of the control routine of ignition timing control. It is a graph which shows an example of the optimal ignition timing with respect to the density | concentration of methane, and a knock ignition timing in a predetermined driving | running state.

  An embodiment of an ignition timing control device and control method will be described with reference to FIGS. With reference to FIG. 1, the overall configuration of an engine system equipped with an ignition timing control device will be described.

  As shown in FIG. 1, the engine 5 of the engine system is a gas engine that uses CNG (Compressed Natural Gas), which is vaporized natural gas, as fuel. The engine 5 is an MPI (Multi Point Injection) engine having a plurality of cylinders 12. In the engine 5, an injector 11 that supplies fuel to intake air flowing into the cylinder 12 is provided in each of the branch pipes 14 a of the intake manifold 14. The engine 5 has a spark plug 13 that ignites the air-fuel mixture in the cylinder 12 for each cylinder 12. The spark plug 13 is, for example, a spark plug that electrically generates a spark. The exhaust gas from each cylinder 12 is discharged to the exhaust manifold 15.

  In the intake passage 16 connected to the intake manifold 14, an air cleaner (not shown), a compressor 18 constituting a turbocharger 17, an intercooler 19, a throttle valve 20, and a surge tank 21 are provided in order from the upstream side. The exhaust passage 22 connected to the exhaust manifold 15 is provided with a turbine 23 that is connected to the compressor 18 via a connecting shaft and constitutes the turbocharger 17.

  The fuel supply device 24 includes a gas tank 25 that stores natural gas at, for example, 20 MPa. A high pressure pipe 26 is connected to the gas tank 25, and a regulator 27 is provided in the high pressure pipe 26. The regulator 27 depressurizes the fuel flowing through the high pressure pipe 26 to, for example, 0.4 MPa. The fuel depressurized by the regulator 27 flows into the delivery pipe 28. A supply pipe 29 is connected to the delivery pipe 28 for each injector 11. The fuel in the delivery pipe 28 is supplied to each injector 11 through a supply pipe 29 for each injector 11.

  The engine system includes an intake air amount sensor 30, an intake pressure sensor 31, an intake air temperature sensor 32, a crank angle sensor 34, a cam angle sensor 35, an air-fuel ratio sensor 36, and an accelerator opening sensor 38.

  The intake air amount sensor 30 detects an intake air amount Qa that is a volume flow rate of intake air flowing through the intake passage 16 upstream of the compressor 18 in the intake passage 16. The intake pressure sensor 31 detects an intake pressure Pb that is the pressure of intake air in the surge tank 21. The intake air temperature sensor 32 detects an intake air temperature Ti that is the temperature of intake air in the surge tank 21. The crank angle sensor 34 detects a crank angle CA that is a rotation angle of the crankshaft 5a. The cam angle sensor 35 outputs a cylinder discrimination signal G at a timing when a predetermined cylinder 12 reaches the compression top dead center based on a rotation angle of a camshaft (not shown). The air-fuel ratio sensor 36 detects the air-fuel ratio AF based on the oxygen concentration contained in the exhaust gas flowing out from the turbine 23. The accelerator opening sensor 38 detects an accelerator opening ACC that is a depression amount of the accelerator pedal 41. The signals output from the sensors 30 to 38 are input to a control device 50 that controls the ignition timing of each spark plug 13.

  The control device 50 is mainly configured by a microcomputer having a CPU, a ROM in which various control programs and various data are stored, and a RAM in which various calculation results and various data are temporarily stored. The control device 50 acquires various information based on signals from the sensors. The control device 50 executes various processes based on various control programs and various data stored in the ROM and information from the sensors 30 to 38. The control device 50 functions as an ignition timing control unit, an intake air / fuel ratio calculation unit, an exhaust air / fuel ratio calculation unit, and a correction amount update unit.

  The control device 50 acquires the intake air amount Qa, the intake pressure Pb, the intake air temperature Ti, the crank angle CA, the cylinder discrimination signal G, the air-fuel ratio AF, and the accelerator opening ACC based on signals from various sensors. The control device 50 acquires the engine speed Ne that is the speed of the crankshaft 5a based on the crank angle CA.

  The control device 50 calculates the fuel supply amount Qf and controls the opening and closing of the injector 11 so that fuel corresponding to the calculated fuel supply amount Qf is supplied. Based on the cylinder discrimination signal G and the crank angle CA, the control device 50 sets a valve opening target that is the injector 11 corresponding to the cylinder 12 that burns the air-fuel mixture. Based on the engine speed Ne and the engine load L, the control device 50 calculates a standard supply amount Qfs when the fuel is a standard fuel. The standard fuel is, for example, a fuel that is used as a reference when designing the engine 5, and is natural gas having a predetermined composition. The control device 50 calculates the fuel supply amount Qf by applying, for example, a feedback value or a learning value calculated by air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 36 to the standard supply amount Qfs. The control device 50 controls opening and closing of the valve opening target so that fuel corresponding to the fuel supply amount Qf is supplied from the valve opening target to the branch pipe 14a. The engine load L is calculated based on, for example, the engine speed Ne, the accelerator opening ACC, the intake air amount Qa, the intake pressure Pb, the intake temperature Ti, and the like. Further, when the control device 50 controls the opening / closing of the valve opening target, for example, the temperature of the fuel and the pressure of the fuel in the delivery pipe 28 may be taken into consideration.

  The control device 50 sets the target air-fuel ratio AFt. Based on the engine speed Ne and the engine load L, the control device 50 calculates a standard air-fuel ratio AFs that is a target air-fuel ratio when the fuel is a standard fuel. The control device 50 sets the target air-fuel ratio AFt by applying, for example, a feedback value or a learning value calculated by air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor 36 to the standard air-fuel ratio AFs.

  The control device 50 controls the opening degree of the throttle valve 20. The control device 50 calculates the weight of the fuel supply amount Qf assuming that the fuel is a standard fuel, and calculates the target air amount Qat based on the calculation result and the target air-fuel ratio AFt. The control device 50 controls the opening of the throttle valve 20 based on the engine speed Ne, the intake pressure Pb, the intake air temperature Ti, and the like so that the air corresponding to the target air amount Qat flows into the cylinder 12. .

The control device 50 controls the driving of the spark plug 13. Based on the cylinder discrimination signal G and the crank angle CA, the control device 50 sets a drive target that is the spark plug 13 corresponding to the cylinder 12 that burns the air-fuel mixture. The control device 50 sets a target ignition timing Atar to be driven, and drives the drive target at the set target ignition timing Atar. The control device 50 corrects the base ignition timing Abse based on the engine speed Ne, the engine load L, and the standard ignition map stored in the ROM by the correction amount Acom as shown in the following equation (1). To set the target ignition timing Atar. The base ignition timing Abse defined in the standard ignition map has the highest engine output among the ignition timings having a predetermined margin with respect to the knock ignition timing at which knocking occurs when the fuel is standard fuel. It is preferable to set an optimal ignition timing that is an ignition timing.
Atar = Abse + Acom (1)

  The control device 50 calculates the exhaust air / fuel ratio AFex of each cylinder 12. The control device 50 calculates the timing at which the exhaust gas discharged from the cylinder 12 reaches the air-fuel ratio sensor 36 for each cylinder 12 based on the cylinder discrimination signal G and the crank angle CA. The control device 50 calculates the exhaust air-fuel ratio AFex of each cylinder 12 based on the air-fuel ratio AF from the air-fuel ratio sensor 36 at that timing.

  The control device 50 updates the correction amount Acom based on the ratio between the exhaust air / fuel ratio AFex and the intake air / fuel ratio AFin. The ratio of the present embodiment is the ratio R (= AFin / AFex) of the intake air-fuel ratio AFin to the exhaust air-fuel ratio AFex. The intake air-fuel ratio AFin is an air-fuel ratio based on the air amount of the air-fuel mixture and the fuel amount of the air-fuel mixture, and is an air-fuel ratio based on the air amount supplied to the cylinder 12 and the fuel amount. The control device 50 calculates the ratio R by treating the target air-fuel ratio AFt as the intake air-fuel ratio AFin. The control device 50 compares the ratio R with the allowable value R1. The allowable value R1 is a value for which it is determined that the composition of the fuel has not changed. For example, the allowable value R1 is not less than the lower limit allowable value R1L smaller than 1 and in the range not smaller than the upper limit allowable value R1H larger than 1. Each value included. The lower limit allowable value R1L is 0.9, for example, and the upper limit allowable value R1H is 1.1, for example.

  When the ratio R is the allowable value R1 (R1L ≦ R ≦ R1H), the control device 50 maintains the current correction amount Acom without updating the correction amount Acom. When the exhaust air-fuel ratio AFex is lower than the intake air-fuel ratio AFin and the ratio R is higher than the allowable value R1 (R1H <R), the control device 50 assumes that the fuel methane concentration has increased, and corrects the current correction. The amount Acom is advanced by the update amount A1. When the exhaust air-fuel ratio AFex is higher than the intake air-fuel ratio AFin and the ratio R is lower than the allowable value R1 (R <R1L), the control device 50 assumes that the concentration of fuel methane has decreased and corrects the current correction The amount Acom is retarded by the update amount A1.

  FIG. 2 is a graph showing an example of the relationship between the ratio R and the update amount A1 of the correction amount Acom. FIG. 2A is a graph when the correction amount Acom before update is the correction amount Acom1. FIG. 2B is a graph in a case where the correction amount Acom before update is the correction amount Acom2 for correcting the base ignition timing Abse to the advance side with respect to the correction amount Acom1. FIG. 2C is a graph in a case where the correction amount Acom before the update is the correction amount Acom3 for correcting the base ignition timing Abse to the retard side with respect to the correction amount Acom1.

  As shown in FIGS. 2A to 2C, the update amount A1 is low when the correction amount Acom before update is the same value and the ratio R is lower than the allowable value R1. In other words, the higher the exhaust air-fuel ratio AFex, the larger the correction amount Acom is retarded. When the update amount A1 is the same as the correction amount Acom before update and the ratio R is higher than the allowable value R1, the correction amount Acom increases as the ratio R increases, that is, the exhaust air-fuel ratio AFex decreases. The value to advance.

  Further, when the correction amount Acom before update advances the base ignition timing Abse, the update amount A1 increases as the advance amount by the correction amount Acom before update increases, even if the ratio R is the same value. Is a value that greatly delays. When the correction amount Acom before update retards the base ignition timing Abse, the update amount A1 decreases as the retardation amount by the correction amount Acom before update increases, even if the ratio R is the same value. This is the value to retard.

  Further, when the correction amount Acom before the update retards the base ignition timing Abse, the update amount A1 increases as the retardation amount by the correction amount Acom before the update increases, even if the ratio R is the same value. Is a value that greatly advances. When the correction amount Acom before update advances the base ignition timing Abse, the update amount A1 decreases as the advance amount by the correction amount Acom before update increases, even if the ratio R is the same value. The value to advance.

  The update amount A1 is, for example, a value determined based on experiments and simulations performed in advance, and the correction amount Acom is adjusted so that the target ignition timing Atar is set to the optimal ignition timing even if the methane concentration changes. The value to be Therefore, the update amount A1 is such that, for example, even if the fuel in the gas tank 25 is switched from standard fuel → other fuel 1 → other fuel 2 → standard fuel, the correction amount Acom becomes 0 by switching to the standard fuel. It is preferable that

  The update amount A1 may be stored as a map in the ROM of the control device 50, and may be obtained by applying the ratio R and the correction amount Acom before update to the map. Further, the update amount A1 may be obtained by substituting each value into a predetermined relational expression including the ratio R and the correction amount Acom before update as parameters.

  With reference to FIG. 3, an example of a control routine of the ignition timing control by the control device 50 will be described. This control routine is repeatedly executed after the engine 5 is started. The correction amount Acom is preferably the initial value of the correction amount Acom when the engine 5 was stopped last time.

  As shown in FIG. 3, first, the control device 50 acquires various information including the fuel supply amount Qf, the target air-fuel ratio AFt, and the target air amount Qat in addition to the information based on the detection values of the various sensors (step S11). . The control device 50 that has acquired the various information sets a drive target based on the crank angle CA and the cylinder discrimination signal G (step S12), and calculates the target air-fuel ratio AFt as the intake air-fuel ratio AFin (step S13). Further, the control device 50 calculates the base ignition timing Abse based on the engine speed Ne, the engine load L, and the standard ignition map (step S14), and adds the correction amount Acom to the base ignition timing Abse to achieve the target. The ignition timing Atar is set (step S15). Then, the control device 50 drives the drive target at the target ignition timing Atar (step S16).

  Next, after calculating the exhaust air-fuel ratio AFex of the cylinder 12 corresponding to the drive target (step S17), the control device 50 calculates the ratio R (step S18). Then, the control device 50 determines whether or not the ratio R is the allowable value R1 (step S19).

  When the ratio R is the allowable value R1 (step S19: YES), the control device 50 once ends a series of processes without updating the correction amount Acom. On the other hand, when the ratio R is not the allowable value R1 (step S19: NO), the control device 50 obtains the update amount A1 based on the ratio R and the correction amount Acom before update, and the amount of the obtained update amount A1. The correction amount Acom is updated by retarding or advancing the correction amount Acom only by this amount (step S20), and the series of processes is temporarily ended.

With reference to FIG. 4, the operation of the control device 50 configured as described above will be described.
As shown in FIG. 4, the optimal ignition timing has a predetermined margin with respect to the knock ignition timing at which knocking occurs with a high probability. For example, if the ignition timing is not adjusted when the methane concentration Cm is reduced from the concentration Cms to the concentration Cm1 by replenishing fuel with respect to the standard fuel, the margin for the knock ignition timing is reduced and knocking is likely to occur. .

  On the other hand, since the stoichiometric air-fuel ratio of methane is larger than the stoichiometric air-fuel ratio of other components such as ethane, when the methane concentration Cm decreases, the amount of oxygen consumed during combustion even with the same air amount and the same fuel amount The exhaust air / fuel ratio AFex becomes higher due to the decrease. That is, when the methane concentration Cm decreases due to fuel replenishment, the ratio R decreases. Conversely, when the methane concentration Cm increases due to fuel replenishment, the ratio R increases.

  The control device 50 compares the ratio R with the allowable value R1, and retards the correction amount Acom when the ratio R is lower than the allowable value R1. As a result, the target ignition timing Atar is controlled to be retarded from before the correction amount Acom is updated.

According to the embodiment, the effects listed below can be obtained.
(1) The occurrence of knocking can be suppressed even when the concentration of methane in the fuel decreases.
(2) Since the target ignition timing Atar is retarded by comparing the ratio R with the allowable value R1, the occurrence of knocking can be suppressed without using a knocking sensor.

  (3) As shown in FIG. 2A, for example, the control device 50 sets the correction amount Acom as the ratio R is lower than the allowable value R1, that is, as the exhaust air-fuel ratio AFex is higher than the intake air-fuel ratio AFin. Retard greatly. As a result, the greater the decrease in the methane concentration, the larger the correction amount Acom is retarded, so that the occurrence of knocking can be suppressed with a higher probability.

  (4) The correction amount Acom updated in accordance with the methane concentration is, in other words, one of the indexes indicating the methane concentration of the fuel. Also, for example, when the methane concentration decreases from a fuel with a methane concentration of 95% and the ratio R decreases to a predetermined value, the methane concentration decreases from the fuel with a methane concentration of 50% and the ratio R In the case of lowering to a predetermined value, the former has a larger reduction amount of methane contained in the fuel.

  In this regard, as shown in FIGS. 2A to 2C, when the correction amount Acom before update advances the base ignition timing Abse, the control device 50 proceeds with the correction amount Acom before update. The greater the angular amount, the greater the retardation of the correction amount Acom. Further, when the correction amount Acom before update retards the base ignition timing Abse, the control device 50 retards the correction amount Acom smaller as the delay amount by the correction amount Acom before update is larger. According to such a configuration, the retardation of the correction amount Acom is adjusted according to the concentration of methane before refueling. Thereby, an excessive decrease in the output of the engine 5 due to the retardation of the correction amount Acom is suppressed.

  (5) The control device 50 advances the correction amount Acom when the ratio R is higher than the allowable value R1. That is, the control device 50 advances the correction amount Acom when the concentration of methane increases due to fuel replenishment and knocking is less likely to occur. As a result, the output of the engine 5 is increased while suppressing the occurrence of knocking.

  (6) For example, as shown in FIG. 2A, the control device 50 increases the correction amount Acom as the ratio R is higher than the allowable value R1, that is, as the exhaust air-fuel ratio AFex is lower than the intake air-fuel ratio AFin. Make a large advance. As a result, the correction amount Acom is advanced as the increase in the methane concentration increases, so that it is possible to advance the base ignition timing Abse according to the increase in the methane concentration while suppressing the occurrence of knocking. is there.

  (7) As described above, the correction amount Acom is one of the indexes indicating the concentration of methane contained in the fuel. Therefore, the larger the advance amount of the base ignition timing Abse by the correction amount Acom, the higher the concentration of methane in the fuel, and the larger the retard amount of the base ignition timing Abse by the correction amount Acom, the lower the concentration of fuel methane.

  In this regard, as shown in FIGS. 2A to 2C, when the correction amount Acom before update advances the base ignition timing Abse, the control device 50 proceeds with the correction amount Acom before update. The larger the angular amount, the smaller the correction amount Acom is advanced. Further, when the correction amount Acom before update retards the base ignition timing Abse, the control device 50 advances the correction amount Acom larger as the delay amount by the correction amount Acom before update increases. That is, the advance angle of the correction amount Acom is adjusted according to the concentration of methane before the fuel is replenished. Thus, it is possible to advance the base ignition timing Abse according to the concentration of methane before refueling and the degree of increase in methane concentration due to fuel replenishment while suppressing the occurrence of knocking.

In addition, the said embodiment can also be suitably changed and implemented as follows.
When the ratio R is a value different from the allowable value R1 and the exhaust air-fuel ratio AFex is lower than the intake air-fuel ratio AFin, the control device 50 does not have to update the correction amount Acom, and the correction amount Acom In the case of advance, the update amount A1 may be a constant value.

  The control device 50 may retard the correction amount Acom when the ratio R is a value different from the allowable value R1 and the exhaust air / fuel ratio AFex is higher than the intake air / fuel ratio AFin. Therefore, the update amount A1 may be a value that changes according to the difference between the ratio R and the allowable value R1, regardless of the correction amount Acom before the update. Further, the update amount A1 may be a constant value regardless of the correction amount Acom before the update and the difference between the ratio R and the allowable value R1.

The allowable value R1 is not limited to a plurality of continuous values, and may be a single value.
The allowable value R1 is not limited to a fixed value, and may vary depending on, for example, the correction amount Acom that is one of the indexes indicating the methane concentration. According to such a configuration, it is possible to set the allowable value R1 suitable for the situation at that time.

  The intake air-fuel ratio AFin is based on, for example, the fuel supply amount based on the detection value of the sensor that measures the mass flow rate of the fuel flowing through the high-pressure pipe 26 and the mass flow rate of the intake air amount based on the detection value of the intake air amount sensor 30. May be calculated. Further, the mass flow rate of the intake air amount may be a value calculated by an arithmetic expression including parameters such as a detection value of the intake pressure sensor 31, a detection value of the intake air temperature sensor 32, and the engine speed Ne.

  The control device 50 may update the correction amount Acom based on the average value Rave of the ratio R in a predetermined period. In such a configuration, control device 50 compares average value Rave with average allowable value R2 having a lower limit value higher than lower limit allowable value R1L and an upper limit value lower than upper limit allowable value R1H. Then, the control device 50 retards the correction amount Acom when the average value Rave is lower than the average allowable value R2, and advances the correction amount Acom when the average value Rave is higher than the average allowable value R2.

  This is because, for example, when the ratio R continues to be the allowable value R1, for example, when the ratio R = 0.96 continues to be continuous in the predetermined period with respect to the allowable value R1 = 0.9 to 1.1. It is assumed that the concentration of methane in the fuel has changed slightly. According to the above configuration, it is possible to cope with such a slight change.

  The ratio R may not be the ratio of the intake air-fuel ratio AFin to the exhaust air-fuel ratio AFex (= AFin / AFex) but the ratio of the exhaust air-fuel ratio AFex to the intake air-fuel ratio AFin (= AFex / AFin). In such a configuration, the correction amount Acom is retarded when the ratio R is larger than the allowable value R1, and the correction amount Acom is advanced when the ratio R is smaller than the allowable value R1.

  The control device 50 can also be applied to an SPI (Single Point Injection) type engine that supplies fuel to each cylinder 12 with one injector. The control device 50 can also be applied to an in-cylinder direct injection engine.

  -The fuel of a gas engine should just be a thing which has methane as a main component, and may be liquefied natural gas (LNG: liquid natural gas), the mixed gas of natural gas, and hydrogen other than CNG. Further, the natural gas may be biomethane gas using as a raw material biogas obtained by methane fermentation of organic waste.

  When the fuel is LNG, a relief valve is attached to the tank that stores the fuel in order to suppress an excessive increase in internal pressure due to evaporation of the fuel. Moreover, since methane has a lower evaporation temperature than other components, it evaporates before other components. Therefore, the decrease in methane concentration also occurs due to the evaporation of methane in the tank and the release of gas through the relief valve.

  DESCRIPTION OF SYMBOLS 5 ... Engine, 5a ... Crankshaft, 11 ... Injector, 12 ... Cylinder, 13 ... Spark plug, 14 ... Intake manifold, 14a ... Branch pipe, 15 ... Exhaust manifold, 16 ... Intake passage, 17 ... Turbocharger, 18 ... Compressor , 19 ... Intercooler, 20 ... Throttle valve, 21 ... Surge tank, 22 ... Exhaust passage, 23 ... Turbine, 24 ... Fuel supply device, 25 ... Gas tank, 26 ... High-pressure piping, 27 ... Regulator, 28 ... Delivery pipe, 29 ... Supply pipe, 30 ... intake air amount sensor, 31 ... intake pressure sensor, 32 ... intake air temperature sensor, 34 ... crank angle sensor, 35 ... cam angle sensor, 36 ... air-fuel ratio sensor, 38 ... accelerator opening sensor, 41 ... accelerator Pedal, 50 ... control device.

Claims (5)

An ignition timing control device for controlling the ignition timing of an engine using natural gas as fuel,
An ignition timing control unit for controlling the ignition timing of the spark plug to a target ignition timing based on a base ignition timing according to an operating state of the engine and a correction amount for correcting the base ignition timing;
An intake air-fuel ratio calculation unit for calculating an intake air-fuel ratio based on the air amount of the mixture and the fuel amount of the mixture;
An exhaust air-fuel ratio calculation unit for calculating an exhaust air-fuel ratio based on the oxygen concentration of the exhaust gas;
A correction amount updating unit that updates the correction amount based on a ratio between the exhaust air-fuel ratio and the intake air-fuel ratio,
The correction amount update unit
The ratio is compared with an allowable value that is a value of the ratio determined that the fuel composition has not changed, and the ratio is different from the allowable value and is greater than the intake air-fuel ratio. An ignition timing control device that retards the correction amount when the exhaust air-fuel ratio is high. The correction amount update unit
The ignition timing control device according to claim 1, wherein the correction amount is retarded more greatly as the exhaust air-fuel ratio is higher than the intake air-fuel ratio. The correction amount update unit
For the above ratio of the same value,
When the correction amount before update advances the base ignition timing, the correction amount is delayed more greatly as the advance amount by the correction amount before update is larger,
The ignition timing control according to claim 2, wherein when the correction amount before updating retards the base ignition timing, the correction amount is retarded smaller as the retardation amount based on the correction amount before updating is larger. apparatus. The correction amount update unit
The ignition timing according to any one of claims 1 to 3, wherein the correction amount is advanced when the ratio is a value different from the allowable value and the exhaust air-fuel ratio is lower than the intake air-fuel ratio. Control device. An ignition timing control method for controlling an ignition timing of an engine using natural gas as fuel,
The control device for controlling the ignition timing is:
While controlling the ignition timing of the spark plug to the target ignition timing based on the base ignition timing according to the operating state of the engine and the correction amount for correcting the base ignition timing,
An intake air-fuel ratio based on the amount of air in the mixture and the amount of fuel in the mixture;
An exhaust air-fuel ratio based on the oxygen concentration of the exhaust gas,
Calculating the ratio of the exhaust air-fuel ratio and the intake air-fuel ratio;
The ratio is compared with an allowable value that is a value of the ratio determined that the fuel composition has not changed, and the ratio is different from the allowable value and is greater than the intake air-fuel ratio. An ignition timing control method that retards the correction amount when the exhaust air-fuel ratio is high.

Images