JP5310413B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to an internal combustion engine mounted on a vehicle and suitable for controlling the fuel injection amount in an internal combustion engine that uses CNG (Compressed Natural Gas) as fuel. The present invention relates to an engine fuel injection control device.

  Conventionally, as disclosed in, for example, Patent Document 1, an internal combustion engine that uses CNG stored in a fuel tank as fuel is known.

JP 7-217485 A Special table 2007-524065 gazette

Incidentally, in the internal combustion engine described above, CO ₂ may be mixed in the fuel tank in addition to CNG. The phase state of CO ₂ changes with temperature and pressure. Since CO ₂ does not burn, whether or not CO ₂ is contained in the fuel gas has a great influence on the air-fuel ratio control, which may deteriorate performance and emissions.

The present invention has been made to solve the above-described problems, and even when CO ₂ mixed in a fuel tank undergoes a phase change, fuel injection of an internal combustion engine that can prevent deterioration in performance and emissions. An object is to provide a control device.

In order to achieve the above object, a first invention is a fuel injection control device for an internal combustion engine,
A fuel tank for storing fuel containing CNG (compressed natural gas) and CO ₂ ;
A fuel injection valve for injecting the fuel supplied from the fuel tank;
A temperature sensor for detecting the temperature of the fuel stored in the fuel tank;
A pressure sensor for detecting the pressure of the fuel stored in the fuel tank;
CO ₂ phase state determination means for determining the phase state of CO ₂ contained in the fuel based on the temperature detected by the temperature sensor and the pressure detected by the pressure sensor;
CO ₂ phase change determination means for determining that the phase state of CO ₂ contained in the fuel has changed between liquid and gas;
When it is determined that the phase state of CO ₂ contained in the fuel has changed from liquid to gas, the fuel injection amount is set to be higher than the first injection amount that achieves the target air-fuel ratio by injecting only CNG. An injection amount changing means for changing to a large amount of the second injection amount;
Fuel injection control means for injecting fuel to the fuel injection valve based on the set fuel injection amount.

The second invention is the first invention, wherein
The fuel injection amount includes a basic injection amount and a correction amount, and the injection amount changing means changes the correction amount to change the setting of the fuel injection amount to the second injection amount.

The third invention is the second invention, wherein
An exhaust gas sensor disposed in an exhaust passage of the internal combustion engine;
Correction amount learning means for learning the correction amount based on the deviation between the actual air-fuel ratio and the target air-fuel ratio obtained from the output of the exhaust gas sensor,
The injection amount changing means clears the correction amount and sets an initial value corresponding to the second injection amount when it is determined that the phase state of CO ₂ has changed from liquid to gas. And

According to the first invention, when CO ₂ in the fuel tank undergoes a phase change from liquid to gas, and the fuel gas supplied to the fuel injection valve becomes a mixed gas of CO ₂ and CNG that does not burn, The setting of the fuel injection amount can be changed so as to be larger than the case where the fuel gas is CNG alone. For this reason, according to the present invention, it is possible to quickly respond to the change in the properties of the fuel, perform fuel injection according to the target air-fuel ratio, and prevent deterioration in engine performance and emissions.

  According to the second invention, the setting of the fuel injection amount can be changed by changing the correction amount. For this reason, according to the present invention, the fuel injection amount can be changed quickly in response to a change in the properties of the fuel without changing the preset basic injection amount corresponding to the operating conditions.

According to the third aspect, when the CO ₂ in the fuel tank undergoes a phase change from liquid to gas, the correction amount can be initialized to an initial value corresponding to the second injection amount. Then, learning of a new correction amount can be started from this initial value. Therefore, according to the present invention, it is possible to reduce the follow-up delay in learning of the fuel injection amount that accompanies a sudden change in fuel properties. Further, even when there is a variation in the CO ₂ concentration of the replenished fuel, the fuel injection amount can be corrected so as to satisfy the target air-fuel ratio.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. Used in the control of the first embodiment of the present invention, a state diagram for explaining CO ₂ phase state map. In Embodiment 1 of this invention, it is a flowchart of the control routine which ECU50 performs.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration according to Embodiment 1 of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. The internal combustion engine 10 has four cylinders 12 arranged in series. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  The intake port of each cylinder 12 is connected to an intake manifold 14. A throttle (not shown) and an air flow meter (not shown) are sequentially provided from the intake manifold 14 toward the upstream side of the intake passage (not shown). Fresh air is taken in from the air flow meter side and supplied to each cylinder 12 via the intake manifold 14. The throttle opening can be arbitrarily controlled by an ECU 50 described later. The present invention is also applicable to a diesel engine that does not include a throttle.

  The intake manifold 14 is provided with one CNG (Compressed Natural Gas) injector 16 toward the intake port of each cylinder 12. Each CNG injector 16 is connected to a CNG delivery pipe 18. The CNG delivery pipe 18 is connected to a fuel tank 22 via a fuel pipe 20. A regulator 24 is provided in the fuel pipe 20. A pressure sensor 26 and a temperature sensor 28 are provided upstream of the regulator 24 on the fuel tank 22 side. CNG is stored in the fuel tank 22 as fuel 30 at a high pressure. The fuel 30 is supplied as fuel gas from the fuel pipe 20 to the CNG injector 16 via the CNG delivery pipe 18.

  The exhaust port of each cylinder 12 is connected to an exhaust manifold 32. The exhaust manifold 32 is connected to the exhaust passage 33. A catalyst 34 is disposed in the exhaust passage 33. For example, a three-way catalyst is used as the catalyst 34. An air-fuel ratio sensor 36 (or oxygen sensor) is provided upstream of the catalyst 34.

  The system of this embodiment includes an ECU (Electronic Control Unit) 50. In addition to the pressure sensor 26, the temperature sensor 28, the air-fuel ratio sensor 36, the air flow meter, the crank angle sensor, the intake air temperature sensor, the cooling water temperature sensor, the intake pressure sensor, and the like are electrically connected to the input side of the ECU 50. Yes. A CNG injector 16, a throttle, and the like are electrically connected to the output side of the ECU 50. The ECU 50 controls the operating state of the internal combustion engine 10 by operating each actuator according to a predetermined program based on the output of each sensor.

  The ECU 50 uses the intake air amount detected by the air flow meter and the outputs of the crank angle sensor, the intake air temperature sensor, the cooling water temperature sensor, the intake air pressure sensor, etc. An injection amount adaptation map that defines a fuel injection amount (hereinafter also referred to as a basic injection amount) corresponding to the fuel ratio 14.6) is stored in advance. For example, the basic injection amount is determined for each operation state so that only CNG (gas of 100% CNG) is injected as fuel gas.

  In the system of the present embodiment, the basic injection amount is acquired from the above-described injection amount matching map according to the operating state. Then, fuel injection control for injecting the fuel 30 from the CNG injector 16 based on the basic injection amount is performed.

  Further, in the system of the present embodiment, air-fuel ratio feedback control of the fuel injection amount is performed based on the output of the air-fuel ratio sensor 36. Specifically, the fuel injection amount is composed of the basic injection amount and the correction amount described above, and the deviation is set to the correction amount so that the actual air-fuel ratio of the exhaust gas flowing into the exhaust passage 33 matches the target air-fuel ratio. Reflect and correct the fuel injection amount. Then, the above-described fuel injection control is performed based on the corrected fuel injection amount.

[Characteristic Control in Embodiment 1]
In the system configuration described above, CNG is stored in the fuel tank 22 as the fuel 30. However, the stored fuel 30 may be mixed with CO ₂ . The concentration of CO ₂ to be mixed is regulated by the country / region. Since CO ₂ does not burn, whether or not CO ₂ is contained in the fuel gas greatly affects air-fuel ratio control. That is, the fuel injection amount for achieving the target air-fuel ratio differs greatly between the case where the fuel gas is only CNG and the case where the fuel gas is a mixed gas of CNG and CO ₂ . For this reason, even when the fuel injection amount is corrected by the air-fuel ratio feedback control described above, it takes time until the control follows, and the emission deteriorates.

Therefore, the system of the present embodiment determines a phase change CO _2, it was decided to CO ₂ changes the settings of the fuel injection quantity in response to the cases of the gaseous fluid.

(CO _two- phase state map)
A more specific outline of control will be described with reference to FIG. Figure 2 is a view for explaining defining the phase state of the CO ₂ "CO ₂ phase state map". Boundary 60 shown in FIG. 2 represents the three states boundary of CO ₂ in accordance with the relationship between the pressure of CO ₂ and temperature. As shown in FIG. 2, the lower the pressure and the higher the temperature, the easier the gas becomes. When the relationship between the pressure of CO ₂ and the temperature exceeds the value of the boundary line 60, CO ₂ is solid (region A) or liquid (region B). On the other hand, if the relationship between the pressure of the CO ₂ and the temperature is below the boundary line 60 CO ₂ is a gas (region C).

The arrow shown in FIG. 2 shows an example of a phase change, and shows that CO _{2 that} is liquid at a certain temperature and pressure changes to gas due to a pressure drop. In the system of the present embodiment, when the internal combustion engine 10 is operated and the fuel 30 in the fuel tank 22 is consumed, the pressure in the fuel tank 22 decreases, so that CO ₂ changes in phase from liquid to gas.

Next, control in the present embodiment using the above-described CO ₂ phase state map will be described. When the temperature of the fuel 30 in the fuel tank 22 and the partial pressure of CO ₂ contained in the fuel 30 are above the boundary line 60, it can be estimated that CO ₂ is a liquid (region B). it can. When CO ₂ is liquid, the gas fuel supplied to the CNG injector 16 does not contain CO _{2 and the} only fuel injected is CNG. Therefore, in this case, by obtaining the basic injection amount corresponding to the operation state from the above-described injection amount conforming map and performing fuel injection based on the basic injection amount, it is possible to realize a suitable performance and emission operation. it can.

On the other hand, when it is below the boundary line 60, it can be estimated that CO ₂ is a gas (region C). When CO ₂ is a gas, CO ₂ is mixed into the gas fuel supplied to the CNG injector 16. Since CO ₂ does not burn, it greatly affects air-fuel ratio control. Therefore, in this case, the fuel injection amount is increased as compared with the case where the above-described CO ₂ is liquid. As a result, the target air-fuel ratio can be achieved quickly, and deterioration of performance and emission can be prevented.

(Control routine)
FIG. 3 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described operation. The routine shown in FIG. 3 is started when the IG switch of the vehicle is turned on (step 100). Here, the ECU 50 sets an initial state of a CO ₂ gas flag and a learning value, which will be described later. The CO ₂ gas flag is set to OFF. The learning value is set to a first learning value described later.

In step 110, the ECU 50 measures the temperature of the fuel 30 in the fuel tank 22 by the temperature sensor 28. At the same time, the pressure of the fuel 30 in the fuel tank 22 is measured by the pressure sensor 26. Then, it is determined phase state of CO ₂ from the CO ₂ phase state map shown in FIG. 2 on the basis of the measured temperature and pressure. Specifically, the partial pressure of CO ₂ is calculated by multiplying the detected pressure by the concentration of CO _{2 in} the fuel defined according to the country / region. Thereafter, it is determined whether or not the relationship between the partial pressure of CO ₂ and the temperature exceeds the boundary line 60 shown in FIG. If so, CO ₂ is determined to be liquid or solid. If below, it is determined that CO ₂ is a gas.

Next, in step 120, it determines whether the phase state of the CO ₂ has changed from the previous state (phase state of CO ₂ it is determined in step 110 in the previous routine). When the CO ₂ gas flag is OFF (including the initial state described above), it is determined at step 110 that CO ₂ is a gas, or when the CO ₂ gas flag is ON, it is determined at step 110 that the CO ₂ is a liquid. If it is, it is determined that the phase state of CO ₂ has changed.

If it is determined that the phase state of CO ₂ has changed, then in step 130, the learning value for injection amount control based on the target air-fuel ratio is cleared. The learning value is a value corresponding to a correction amount for correcting the basic injection amount acquired from the injection amount matching map based on the operating state.

Subsequently, in skip 140, it is determined whether or not the phase state of CO ₂ is liquid. Specifically, it is determined based on the determination result in step 110 whether or not the phase state of CO ₂ is liquid. When the phase state of the CO ₂ is determined to be liquid, CO ₂ together with the decision result in step 120 is a phase change from a gas to a liquid. In this case, in step 150, the first learning value is set as the initial value of the learning value. The first learning value is 0 when the injection amount adaptation map is adapted at CNG 100%.

  Learning based on the above-described air-fuel ratio feedback control is performed using the set learning value as an initial value (step 160). Specifically, the learned value is corrected so that the deviation between the actual air-fuel ratio obtained from the output of the air-fuel ratio sensor 36 provided upstream of the catalyst 34 and the target air-fuel ratio is zero.

On the other hand, in step 140, when the phase state of the CO ₂ is determined to be liquid, CO ₂ together with the decision result in step 120 is a phase change from a gas to a liquid. In this case, in step 170, the second learning value is set as the initial value of the learning value. The second learning value is a learning value determined so as to meet the target air-fuel ratio by adapting to the fuel at the center of the CO ₂ mixture ratio defined for each country / region, and is higher than the first learning value. .

  Thereafter, similar to step 160 described above, learning based on air-fuel ratio feedback control is performed using the set learning value as an initial value.

If it is determined in step 120 that there is no phase change in CO ₂ , learning based on the air-fuel ratio feedback control is continued for the learning value learned in step 160 of the previous routine (step 160).

In step 180, the CO ₂ phase state is stored. Specifically, if it is determined in step 110 that CO ₂ is liquid or solid, the CO ₂ gas flag is set to OFF. On the other hand, if it is determined in step 110 that CO ₂ is a gas, the CO ₂ gas flag is set to ON. The set CO ₂ gas flag is used in the processing of step 120 in the next routine.

  In step 190, it is determined whether or not the IG switch is OFF. If it is determined that the IG switch is ON, it is still in operation and the next routine is started from step 110. If it is determined that the IG switch is OFF, this routine is terminated.

As described above, according to the routine shown in FIG. 3, even if the CO ₂ in the fuel tank 22 undergoes a phase change, the initial value of the learning value is switched to achieve the target air-fuel ratio. The injection amount can be changed. For this reason, according to the system of the present embodiment, it is possible to reduce the follow-up delay of the learning of the correction amount due to the sudden change in fuel properties, and to prevent deterioration of the engine performance and emission.

  Further, according to the system of the present embodiment, it is difficult to provide a sensor for detecting the property of the fuel 30 at a high pressure on the fuel line, but based on the outputs of the pressure sensor 26 and the temperature sensor 28 provided upstream of the regulator 24. The property of the fuel 30 in the fuel tank 22 can be estimated.

By the way, in the system of the first embodiment described above, the setting of the fuel injection amount when the phase change of CO ₂ is switched by changing the initial value of the learning value. Is not limited to this. In place of the processing of steps 130 and 150 to 170, the first injection amount adaptation map that determines the injection amount that achieves the target air-fuel ratio by adapting to the fuel gas of only CNG, and the mixed gas of CNG and CO ₂ And a second injection amount adaptation map that defines the injection amount that achieves the target air-fuel ratio, and changes the setting of the fuel injection amount by switching the injection adaptation map that is used when the phase of CO ₂ changes It is good to do.

  In the system of the first embodiment described above, the internal combustion engine 10 is an engine that uses CNG, but it may be a bi-fuel engine that uses CNG and gasoline as fuel.

  In the system of the first embodiment described above, the CNG injector 16 directed to the intake port is provided in the intake manifold 14 and port injection is performed. However, the injector may be provided in the cylinder and directly injected. .

In the first embodiment described above, the fuel tank 22 is the “fuel tank” in the first invention, the CNG injector 16 is the “fuel injection valve” in the first invention, and the temperature sensor 28 is the first fuel tank. The pressure sensor 26 is the “pressure sensor” in the first invention, the fuel injection control by the ECU 50 is the “fuel injection control means” in the first invention, the air-fuel ratio sensor 36 Corresponds to the “exhaust gas sensor” in the third aspect of the invention.
In addition, here, the ECU 50 executes the process of step 110, so that the “CO ₂ phase state determination means” in the first invention executes the process of step 120, thereby executing the process of the first invention. When the “CO ₂ phase change determining means” executes the process of step 170, the “injection amount changing means” in the first to third inventions executes the process of step 160, thereby executing the third step. Each of the “correction amount learning means” in the present invention is realized.
Further, in the first embodiment, the second learning value set in step 170 corresponds to the “initial value” in the third invention.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder 14 Intake manifold 16 CNG injector 18 CNG delivery pipe 20 Fuel piping 22 Fuel tank 24 Regulator 26 Pressure sensor 28 Temperature sensor 30 Fuel 32 Exhaust manifold 33 Exhaust passage 34 Catalyst 36 Air-fuel ratio sensor 50 ECU
60 border

Claims (3)

A fuel tank for storing fuel containing CNG (compressed natural gas) and CO ₂ ;
A fuel injection valve for injecting the fuel supplied from the fuel tank;
A temperature sensor for detecting the temperature of the fuel stored in the fuel tank;
A pressure sensor for detecting the pressure of the fuel stored in the fuel tank;
CO ₂ phase state determination means for determining the phase state of CO ₂ contained in the fuel based on the temperature detected by the temperature sensor and the pressure detected by the pressure sensor;
CO ₂ phase change determination means for determining that the phase state of CO ₂ contained in the fuel has changed between liquid and gas;
When it is determined that the phase state of CO ₂ contained in the fuel has changed from liquid to gas, the fuel injection amount is set to be higher than the first injection amount that achieves the target air-fuel ratio by injecting only CNG. An injection amount changing means for changing to a large amount of the second injection amount;
Fuel injection control means for injecting fuel to the fuel injection valve based on the set fuel injection amount;
A fuel injection control device for an internal combustion engine, comprising: The fuel injection amount includes a basic injection amount and a correction amount,
The injection amount changing means changes the setting of the fuel injection amount to the second injection amount by changing the correction amount;
The fuel injection control device for an internal combustion engine according to claim 1. An exhaust gas sensor disposed in an exhaust passage of the internal combustion engine;
Correction amount learning means for learning the correction amount based on the deviation between the actual air-fuel ratio and the target air-fuel ratio obtained from the output of the exhaust gas sensor,
The injection amount changing means clears the correction amount and sets an initial value according to the second injection amount when it is determined that the phase state of CO ₂ has changed from liquid to gas.
The fuel injection control device for an internal combustion engine according to claim 2.

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