JP3814913B2 - Control device for gas fuel internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a gas fuel internal combustion engine.
[0002]
[Prior art]
For example, in a gas fuel internal combustion engine as disclosed in Japanese Utility Model Laid-Open No. 6-80825, the throttle opening is usually determined according to the amount of depression of the accelerator pedal, and the optimum amount for the intake air amount determined according to the throttle opening. The gas fuel is supplied to the engine.
[0003]
[Problems to be solved by the invention]
By the way, it is known that the gas composition of gas fuel varies depending on the production area, production time, season, and the like. However, if the gas composition varies, the calorific value per unit volume of the gas fuel will vary. Therefore, even if the optimal amount of gas fuel is supplied to the intake air amount, the engine output will vary. There is a problem that it will occur. In other words, excess or deficiency occurs in the engine output, and thus good drivability cannot be ensured.
[0004]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION In order to solve the above SL problem, reference gas composition base is the throttle opening required to match the engine output torque to the required torque when the gas composition of the gas fuel is the reference gas composition Means for calculating the throttle opening based on the accelerator pedal depression amount, means for detecting the engine output torque, and calculating the reference gas composition output torque that is the engine output torque when the gas composition of the gas fuel is the reference gas composition Means for calculating the gas composition correction coefficient based on the engine output torque and the reference gas composition output torque, and calculating the throttle opening by correcting the reference gas composition basic throttle opening by the gas composition correction coefficient And a control device for a gas fuel internal combustion engine, comprising: means for calculating a fuel injection amount in accordance with an intake air amount determined in accordance with a throttle opening It is provided.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, 1 is a cylinder block, 2 is a piston, 3 is a cylinder head, 4 is a combustion chamber, 5 is an intake valve, 6 is an exhaust valve, 7 is an intake port, 8 is an exhaust port, and 9 is a combustion chamber 4. Each of the spark plugs arranged inside is shown. Each intake port 7 is connected to a common surge tank 11 via a corresponding intake branch pipe 10, and the surge tank 11 is connected to an air cleaner 13 via an intake duct 12. In each intake branch pipe 10, a fuel injection valve 14 for injecting compressed natural gas (hereinafter referred to as CNG) as gas fuel is disposed in the corresponding intake branch pipe 10. Further, a throttle valve 15 driven by an actuator 15a made of, for example, a step motor is disposed in the intake duct 12. On the other hand, the exhaust port 8 is connected to a catalytic converter 18 containing a three-way catalyst 17 via a common exhaust manifold 16, and the catalytic converter 18 is connected to an exhaust pipe 19.
[0006]
The electronic control unit 20 is composed of a digital computer and includes a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a CPU (Microprocessor) 24, an input port 25, which are connected to each other via a bidirectional bus 21. And an output port 26. An intake pressure sensor 27 that generates an output voltage proportional to the intake pressure is attached to each intake branch pipe 10. An in-cylinder pressure sensor 28 that generates an output voltage proportional to the in-cylinder pressure is attached to the cylinder head 3, and an air-fuel ratio sensor 29 for detecting the air-fuel ratio is attached to a collecting portion of the exhaust manifold 16. The accelerator pedal 30 is connected to a depression amount sensor 31 that generates an output voltage proportional to the depression amount. The output voltages of the intake pressure sensor 27, the in-cylinder pressure sensor 28, the air-fuel ratio sensor 29, and the depression amount sensor 31 are input to the input port 25 via corresponding AD converters 32, respectively. Further, a crank angle sensor 33 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees is connected to the input port 25. The CPU 24 calculates the intake air amount based on the output signal of the intake pressure sensor 27, and calculates the engine speed based on the output pulse of the crank angle sensor 33. On the other hand, the output port 26 is connected to each spark plug 9, each fuel injection valve 14, and actuator 15 a via a corresponding drive circuit 34.
[0007]
By the way, in the internal combustion engine of FIG. 1, the opening degree of the throttle valve 15, that is, the throttle opening degree TA is calculated based on the following equation.
TA = TABS / KTA
Here, TABS represents a reference gas composition basic throttle opening, and KTA represents a gas composition correction coefficient.
[0008]
The reference gas composition basic throttle opening degree TABS is the throttle opening required for making the engine output torque coincide with the required torque determined according to the depression amount DEP of the accelerator pedal 30 when the gas composition of CNG is a reference gas composition to be described later. It is a degree and has been obtained by experiments in advance. This TABS increases as the depression amount DEP of the accelerator pedal 30 increases as shown in FIG. This TABS is stored in advance in the ROM 22 as a function of DEP in the form of a map shown in FIG.
[0009]
The gas composition correction coefficient KTA is for correcting the reference gas composition basic throttle opening degree TABS according to the gas composition of CNG. When no correction is required, that is, when the gas composition of CNG is the reference gas composition, KTA = 1.
On the other hand, in the internal combustion engine of FIG. 1, the fuel injection time TAU is calculated based on the following equation.
TAU = TBS / FAF / KK
Here, TBS indicates a reference gas composition basic fuel injection time, FAF indicates a feedback correction coefficient, and KK indicates a correction coefficient.
[0010]
The reference gas composition basic fuel injection time TBS is an injection time required to make the air-fuel ratio coincide with the target air-fuel ratio, for example, the stoichiometric air-fuel ratio when the gas composition of the CNG is the reference gas composition, and is obtained in advance by experiments. . This TBS is stored in advance in the ROM 22 in the form of a map shown in FIG. 3 as a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N.
[0011]
The feedback correction coefficient FAF is for making the air-fuel ratio coincide with the stoichiometric air-fuel ratio based on the output signal of the air-fuel ratio sensor 29. Note that the feedback correction coefficient FAF varies around 1.0.
The correction coefficient KK is a summary of the warm-up increase correction coefficient, the acceleration increase correction coefficient, and the like, and is set to 1.0 when correction is not necessary.
[0012]
Thus, the throttle opening TA is controlled according to the depression amount DEP of the accelerator pedal 30, and the fuel injection time TAU is calculated according to the intake air amount Q determined according to the throttle opening TA. As long as the composition is the reference gas composition, the engine output torque can be matched to the required torque. That is, the actual output torque does not become excessive or deficient, and therefore, good drivability is ensured.
[0013]
By the way, as described at the beginning, the gas composition of CNG varies. However, if there is a variation in the gas composition of CNG in this way, the amount of heat generated by CNG will vary. That is, the CNG of the internal combustion engine of FIG. 1 is generally composed of four components of methane, ethane, propane, and butane, but the calorific value per unit mixture volume varies for each component as shown in FIG. Therefore, if there is a variation in the gas composition of CNG, the amount of heat generated per unit CNG volume will vary. On the other hand, the engine output torque is proportional to the total calorific value of the gas fuel supplied into the combustion chamber 4. Therefore, if the amount of heat generated by CNG varies, even if the fuel injection time TAU is the same, the engine output torque varies. In other words, even if the depression amount DEP of the accelerator pedal 30 is the same, the output torque varies, that is, the actual output torque is excessive or insufficient with respect to the required torque determined according to the depression amount DEP of the accelerator pedal 30. Become. In this case, for example, if the output torque is insufficient at the time of acceleration, a good vehicle acceleration feeling cannot be obtained, and thus good drivability cannot be ensured.
[0014]
On the other hand, the engine output torque can be controlled by controlling the throttle opening degree TA. Therefore, in the embodiment according to the present invention, a representative value representative of the heat generation amount of CNG is obtained, the gas composition correction coefficient KTA is calculated according to this representative value, and the reference gas composition basic throttle opening degree TABS is corrected by this KTA. I am doing so. As a result, the actual output torque can be matched with the required torque regardless of the gas composition of CNG, and thus good drivability can be ensured.
[0015]
Next, a method for calculating the gas composition correction coefficient KTA will be described.
Considering that the net thermal efficiency of the internal combustion engine is substantially constant regardless of the gas composition of CNG, the following equation holds for the same engine speed N and the same fuel injection time TAU.
a · N · TRQ / QEX = a · N · TRQS / QEXS
Here, a is a constant that collectively represents the heat equivalent of work, TRQ is the output torque at a certain gas composition, QEX is the total calorific value of CNG supplied to the engine at a certain gas composition, TRQS represents output torque at the reference gas composition (hereinafter referred to as reference gas composition output torque), and QEXS represents the total calorific value of CNG supplied to the engine at the reference gas composition. Therefore, the following relationship is obtained.
[0016]
QEX = TRQ ・ QEXS / TRQS
That is, the amount of heat generated by CNG is represented by the engine output torque TRQ. Therefore, in the embodiment according to the present invention, the engine output torque TRQ is detected, and the gas composition correction coefficient KTA is calculated based on the detected output torque TRQ.
FIG. 5 shows the gas composition correction coefficient KTA. As shown in FIG. 5, when the detected output torque TRQ is smaller than the reference gas composition output torque TRQS, that is, when TRQ / TRQS <1, the gas composition correction coefficient KTA is larger than 1, and TRQ / TRQS is smaller. As it grows. Therefore, when TRQ / TRQS <1, the throttle opening degree TA is corrected to be increased, and thus the output torque is increased. On the other hand, when TRQ / TRQS> 1, the gas composition correction coefficient KTA is smaller than 1, and decreases as TRQ / TRQS increases. Therefore, when TRQ / TRQS> 1, the throttle opening degree TA is corrected to decrease, and thus the output torque is decreased.
[0017]
In this way, it is possible to make the actual output torque coincide with the required torque regardless of the gas composition of CNG, and therefore it is possible to prevent the output torque from being excessive or insufficient. As a result, good drivability can be ensured regardless of the gas composition of CNG.
Any reference gas composition of CNG may be used, but in this embodiment, the gas composition of the city gas 13A is used as the reference gas composition. The reference gas composition is generally as follows.
Methane: 87.5%
Ethane: 7.6%
Propane: 2.3%
Butane: 2.6%
The output torque TRQ may be obtained in any way. In this embodiment, the output torque TRQ is calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor 28 as described in Japanese Patent Publication No. 7-89090. I am trying to calculate. However, a torque sensor may be attached to the crankshaft, or the output torque may be obtained based on the angular velocity of the crankshaft as described in, for example, Japanese Patent Publication No. 7-33809.
[0018]
FIG. 6 shows a routine for controlling the throttle opening. This routine is executed in a main routine that is repeatedly executed, for example.
Referring to FIG. 6, first, at step 40, the reference gas composition basic throttle opening degree TABS is calculated using the map of FIG. In the following step 41, the output torque TRQ is detected based on the output signal of the in-cylinder pressure sensor 28. In the subsequent step 42, the reference gas composition output torque TRQS is calculated. Reference gas composition output torque TRQS is obtained in advance by experiments, and is stored in advance in ROM 22 in the form of a map shown in FIG. 7 as a function of engine load Q / N and engine speed N as shown in FIG. . In the following step 43, the gas composition correction coefficient TKA is calculated using TRQ / TRQS and the map of FIG. At the next step 44, the throttle opening degree TA is calculated as the product of the reference gas composition basic throttle opening degree TABS and the gas composition correction coefficient KTA. In the following step 45, the actuator 15a is driven so that the actual throttle opening becomes TA.
[0019]
FIG. 8 shows a routine for calculating the fuel injection time TAU. This routine is executed in a main routine that is repeatedly executed, for example.
Referring to FIG. 8, first, at step 50, the reference gas composition basic fuel injection time TBS is calculated using the map of FIG. In the following step 51, the feedback correction coefficient FAF is calculated based on the output signal of the air-fuel ratio sensor 29. In the following step 52, the correction coefficient KK is calculated. In the following step 53, the fuel injection time TAU is calculated based on the following equation.
[0020]
TAU = TBS / FAF / KK
CNG is injected from the fuel injection valve 14 by TAU.
In addition to CNG, natural gas and petroleum gas which are primary fuels, such as liquefied petroleum gas (LPG), etc., and coal conversion gas and petroleum conversion gas which are secondary fuels can be used as gas fuel. In addition, the present invention can be applied to an internal combustion engine that uses methanol or the like, which is a liquid fuel, but whose composition may vary.
[0021]
【The invention's effect】
Regardless of the gas composition of the gas fuel, it is possible to prevent the engine output from being excessive or deficient, so that good drivability can be ensured.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram showing a reference gas composition basic throttle opening.
FIG. 3 is a diagram showing a reference gas composition basic fuel injection time.
FIG. 4 is a diagram showing a calorific value per unit volume of each component of CNG.
FIG. 5 is a diagram showing a gas composition correction coefficient.
FIG. 6 is a flowchart for controlling the throttle opening.
FIG. 7 is a diagram showing a reference gas composition output torque.
FIG. 8 is a flowchart for calculating a fuel injection time.
[Explanation of symbols]
4 ... Combustion chamber 7 ... Intake port 14 ... Fuel injection valve 15 ... Throttle valve 15a ... Actuator 28 ... In-cylinder pressure sensor 30 ... Accelerator pedal

Claims (1)

  Means for calculating a reference gas composition basic throttle opening, which is a throttle opening required to make the engine output torque coincide with the required torque when the gas composition of the gas fuel is the reference gas composition, based on the depression amount of the accelerator pedal; A means for detecting engine output torque, a means for calculating a reference gas composition output torque, which is an engine output torque when the gas composition of the gas fuel is a reference gas composition, and an engine output torque and a reference gas composition output torque. Means for calculating the gas composition correction coefficient, means for calculating the throttle opening by correcting the basic gas composition basic throttle opening with the gas composition correction coefficient, and the intake air amount determined according to the throttle opening. A control device for a gas fuel internal combustion engine, comprising: means for calculating a fuel injection amount;

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