JP4120182B2 - Fuel injection control device for CNG engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection control device for a CNG engine, and in particular, even when gas fuel is supplied that has a calorific value and a gas composition that are different from the set gas fuel and the air-fuel ratio tends to be on the lean side. The fuel injection of the CNG engine that can avoid the inconvenience that the feedback control is not performed normally without the sensor being activated, can eliminate the need for preparing a control specification dedicated to each gas fuel, and can contribute to a reduction in design man-hours The present invention relates to a control device.
[0002]
[Prior art]
An engine mounted on a vehicle is provided with an injector for injecting liquid fuel, and fuel injection for controlling the injector so that the air-fuel ratio of the intake passage determined from the detection signal of the air-fuel ratio sensor provided in the exhaust passage becomes the target air-fuel ratio. Some have a control device. This fuel injection control device performs feedback control so that the three-way catalyst has good purification characteristics near the stoichiometric air-fuel ratio in the low-medium load range, but is open so that the output air-fuel ratio is in the full-load range where the throttle valve is fully open. It is normal to control the loop.
[0003]
An engine mounted on a vehicle is a CNG engine in which CNG (compressed natural gas), which is gas fuel, is injected and supplied from an injector as fuel. Also in the fuel injection control device of this CNG engine, as described above, feedback control is performed so that the air-fuel ratio is close to the stoichiometric air-fuel ratio in the low-medium load region, and open-loop control is performed so that the output air-fuel ratio is in the entire load region. Has an advantage.
[0004]
An example of such a fuel injection control device for a CNG engine is disclosed in Japanese Patent Laid-Open No. 10-148143. The disclosed technique sets a required air-fuel ratio corresponding to the composition value detected by the vaporized gas composition detecting means, sets an air-fuel ratio correction coefficient for correcting the fuel injection amount based on the required air-fuel ratio, and at least engine operation. The fuel injection amount for the injector is set based on the state and the air-fuel ratio correction coefficient.
[0005]
[Problems to be solved by the invention]
However, in the fuel injection control device of a CNG engine, since the supplied fuel is gas fuel, it is greatly affected by fluctuations in factors such as fuel temperature, fuel pressure, intake air temperature, etc., and correction based on these factors is performed. Even so, there is a problem that it is difficult to stably control the output air-fuel ratio in the open loop control.
[0006]
Further, city gas based on natural gas, which is gas fuel supplied to the CNG engine, is supplied with a gas called 13A in most regions. When setting the control specification of the CNG engine, it is usually set based on the calorific value and gas composition of 13A gas supplied in most areas.
[0007]
However, city gas called 12A, which has a calorific value and gas composition different from 13A gas in some areas, is supplied to the city gas. Therefore, there are two types of city gas supplied to the CNG engine: 13A gas and 12A gas having different calorific values and gas compositions. For this reason, when 12 A gas is supplied to a CNG engine set with 13 A gas, there is a problem that exhaust purification performance and drivability deteriorate.
[0008]
Such a problem can be dealt with to some extent by adding learning control to control of the fuel injection amount. However, in the learning control of the fuel injection amount of the CNG engine, the learning value is set so that the control center of the feedback control becomes plus (+) / minus (−) 0%.
[0009]
For this reason, when learning control is performed so that the control center of feedback control becomes (+) / minus (−) 0% by 13A gas, 12A gas having a different calorific value and gas composition after using 13A gas as fuel. When the fuel is charged as fuel, the air-fuel ratio becomes leaner, and the air-fuel ratio leaning does not activate the O2 sensor, which is the air-fuel ratio sensor, and the air-fuel ratio feedback control is not normally performed.
[0010]
In order to cope with such two types of gas fuels having different calorific values and gas compositions, it is necessary to prepare control specifications for each gas fuel in the fuel injection control device. There is an inconvenience that causes an increase.
[0011]
[Means for Solving the Problems]
Therefore, in order to eliminate the above-mentioned inconvenience, the present invention provides an air-fuel ratio sensor in the exhaust passage of a CNG engine that can supply both types of gas fuels having different calorific values and gas compositions by an injector, and performs feedback control. Air-fuel ratio control means for feedback-controlling the fuel injection amount by a feedback correction coefficient is provided so that the air-fuel ratio obtained from the detection signal of the air-fuel ratio sensor when the condition is satisfied becomes the target air-fuel ratio, and the air-fuel ratio sensor when the learning condition is satisfied stores the value corresponding to the difference as a learning value and the air-fuel ratio and the target air-fuel ratio obtained from the detection signal of the learning control means for learning control to update the learning value the storage provided, a basic fuel injection amount gas fuel to the CNG engine by a value obtained by correcting the learning value and the feedback correction coefficient The fuel injection control apparatus for CNG engine provided with a fuel supply control means controls the operation of the injector to inject supply, the learning control means, the output air-fuel ratio with always a value richer than the stoichiometric air-fuel ratio of the base air-fuel ratio It is characterized by learning control so that
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The fuel injection control device for a CNG engine according to the present invention has a learning value that is rich even when gas fuel is supplied that has a calorific value and a gas composition that are different from the set gas fuel and the air-fuel ratio tends to be on the lean side. Therefore, it is possible to activate the air-fuel ratio sensor by preventing leaning of the air-fuel ratio, and in order to cope with two types of gas fuels having different calorific values and gas compositions, the fuel injection control device is provided with each gas. There is no need to prepare fuel-specific control specifications.
[0013]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 show an embodiment of the present invention. In FIG. 8, 2 is a CNG engine to which CNG (compressed natural gas) is supplied as gas fuel mounted on a vehicle (not shown). The CNG engine 2 forms an intake passage 12 by an air cleaner 4, an intake pipe 6, a throttle body 8 and an intake manifold 10 as an intake system, a throttle valve 14 is provided in the throttle body 8, and each cylinder (see FIG. An injector 16 corresponding to (not shown) is provided. In the CNG engine 2, an exhaust passage 24 is formed by an exhaust manifold 18, an exhaust pipe 20, and a muffler 22 as an exhaust system, and a three-way catalyst 26 is provided immediately downstream of the exhaust manifold 18.
[0014]
This CNG engine 2 is provided with an intake air temperature sensor 28 for detecting the intake air temperature of the intake passage 12, a throttle sensor 30 for detecting the throttle opening of the throttle valve 14, and an idle switch that is turned on when the throttle valve 14 is idle. 32, a fully open switch 34 that is turned on when the throttle valve 14 is fully opened, an intake pipe pressure sensor 36 that detects the intake pipe pressure, and a water temperature sensor 38 that detects the cooling water temperature of the engine 2 are provided. A cam angle sensor 40 that constitutes a variable valve timing device (VVT) that does not operate is provided, an engine speed sensor 42 that detects the engine speed is provided, and an O2 sensor 44 that is an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gas is provided. .
[0015]
The CNG engine 2 is provided with a gas fuel container 46 for storing CNG as gas fuel. Two gas fuel containers 46 are provided and communicated with each other through a communication pipe 48. One gas fuel container 46 is connected to one end of the fuel supply pipe 50. The other end of the fuel supply pipe 50 is connected to the injector 16. A main stop valve 52, a remaining pressure sensor 54, a gas filter 56, a high pressure regulator 58, a fuel pressure sensor 60, and a fuel temperature sensor 62 are interposed in the fuel supply pipe 50 sequentially from the gas fuel container 46 side. Provided.
[0016]
The main stop valve 52 is installed close to the gas fuel container 46 and shuts off CNG when the CNG engine 2 is stopped. A digital fuel gauge 64 and an analog fuel gauge 66 are connected to the remaining pressure sensor 54. The gas filter 56 filters CNG. The high pressure regulator 58 depressurizes CNG and adjusts it to an appropriate pressure and flow rate. The fuel pressure sensor 60 detects the pressure of CNG. The fuel temperature sensor 62 detects the temperature of CNG.
[0017]
Further, one end of a fuel filling pipe 68 is connected to the other gas fuel container 46. A filling port 70 is provided on the other end side of the fuel filling pipe 68. When filling the gas fuel container 46 with CNG as gas fuel, the filling port 70 is connected to a filling device of a filling device (not shown). The fuel filling pipe 68 is provided with a fuel filling valve 72 and a check valve 74 sequentially from the filling port 70 side.
[0018]
The injector 16, the intake air temperature sensor 28, the throttle sensor 30, the idle switch 32, the fully open switch 34, the intake pipe pressure sensor 36, the water temperature sensor 38, the cam angle sensor 40, the rotation speed sensor 42, the O2 sensor 44, and the main stop valve 52. The fuel pressure sensor 60 and the fuel temperature sensor 62 are connected to the control unit 78 of the fuel injection control device 76. The controller 78 determines the operating state based on signals input from the various sensors 28 to 44 and 60 to 62, and controls the operation of the injector 16 and the main stop valve 52.
[0019]
The control unit 78 includes an air-fuel ratio control unit 80, a learning control unit 82, and a fuel supply control unit 84. The air-fuel ratio control means 80 feedback-controls the fuel injection amount with a feedback correction coefficient so that the air-fuel ratio of the intake passage 12 obtained from the detection signal of the O2 sensor 44 becomes the target air-fuel ratio when the feedback control condition is satisfied.
[0020]
The learning control unit 82 stores a value corresponding to the difference between the air-fuel ratio obtained from the detection signal of the O2 sensor 44 and the target air-fuel ratio as a learning value when the learning condition is satisfied, and updates the stored learning value. Control learning. The fuel supply control means 84 controls the operation of the injector 16 so as to inject and supply CNG to the CNG engine 2 with a value obtained by correcting the basic fuel injection amount with the feedback correction coefficient and the learned value.
[0021]
The fuel injection control device 76 of the CNG engine 2 changes the learning control threshold value of the learning control means 82 so that the base air-fuel ratio becomes the output air-fuel ratio when the feedback region is deviated.
[0022]
Further, the fuel injection control device 76 of the CNG engine 2 is provided with an output air-fuel ratio control means 86 in the control unit 78. The output air-fuel ratio control means 86 performs learning by the learning control means 82 so that the air-fuel ratio obtained from the detection signal of the O2 sensor 44 becomes the output air-fuel ratio when the fully open condition where the throttle valve 14 of the CNG engine 2 is fully open is satisfied. The fuel injection amount is subjected to open loop control based on the learned value.
[0023]
Next, the operation will be described.
[0024]
The fuel injection control device 76 of the CNG engine 2 controls the operation of the injector 16 and the main stop valve 52 by the operation of the control unit 78 based on signals input from the various sensors 28 to 44 and 60 to 62.
[0025]
As shown in FIG. 1, when the fuel injection control device 76 starts the control by starting the CNG engine 2 (100), the basic injection amount is controlled by open loop control (102), and the air-fuel ratio feedback control condition It is determined whether or not is established (104). As shown in FIG. 4, the air-fuel ratio control is performed in a region set by the engine speed and the intake pipe pressure and the fully open switch 34 of the throttle valve 14 is OFF.
[0026]
If this determination (104) is NO, the processing returns to the processing (102). If this determination (104) is YES, feedback control is started and the fuel injection amount is feedback controlled by a feedback correction coefficient (106), and it is determined whether or not a learning control condition is satisfied (108).
[0027]
If this determination (108) is NO, the processing returns to (106). If this determination (108) is YES, the learning control is started with the threshold value of the learning control changed so that the base air-fuel ratio becomes the output air-fuel ratio when the feedback region is deviated (110). The learning value is learned so that the air-fuel ratio becomes an output air-fuel ratio richer than the stoichiometric air-fuel ratio, and the learning value on the rich side is held and updated (112), and whether or not the fully open switch 34 of the throttle valve 14 is ON. Is determined (114).
[0028]
The learning control satisfies, for example, all the following conditions as learning conditions, and updates the learning value M for each operation zone shown in FIG. 4 after XFLRTM [sec] has elapsed.
(1) During feedback control (2) Boost pressure (intake pipe pressure)
Pb <(TFBPRSL (Ne), Pa + TAPFB (Ne) min)
/ (TFBPRSL (Ne), Pa + TAPFB (Ne) min
-XCLHYS) [kPa]
(3) The water temperature sensor 38 is normal,
XFLRNWH [degree C]> cooling water temperature WT ≧ XFLRNW [degree C]
(4) Intake air temperature sensor 28 is normal, AT <XFLRNAH [degree C]
(5) Fuel end sensor 62 is normal (6) Acceleration is not increasing (Qacc = 0)
(7) Deceleration is not being reduced (Qdec = 0)
(8) Boost pressure (intake pipe pressure) Pb ≧ XFLPRS [kPa]
(9) Throttle sensor 30 is normal (10) O2 sensor 44 does not cross X02CHL [V] for X02TST [sec] during feedback after O2 sensor 44 crosses X02CHL [V] after elapse of t [sec] after starting Until time.
(11) The amount is not increasing immediately after starting.
(12) Cam angle sensor 40 is normal, OCV (VVT oil control valve) current is normal, VVT (variable valve timing device) advance angle control is normal.
In the learning control, the learning value Cstdy of the air-fuel ratio is learned by the following learning method as shown in FIGS.
(1) Immediately after the battery is turned off, Cstdy = 1.0.
(2) When the power is cut off (ignition switch OFF), Cstdy is stored and retained by battery backup.
(3) A learning value is calculated from the equation shown in FIG. 5 every t [sec].
(4) As shown in FIG. 6, learning values are learned using various values as data,
Restrict to XDFLLOS ≦ Cstdy ≦ XDFLUPS.
[0030]
If the determination (114) as to whether or not the fully open switch 34 is ON is NO, the process returns to the process (106). If the determination (114) as to whether or not the fully open switch 34 is ON is YES, the open loop control is performed so that the output air-fuel ratio is set to the rich learning value held (116).
[0031]
During the open loop control (116), it is determined whether or not the fully open switch 34 of the throttle valve 14 is ON (114). If this determination (114) is NO, the process returns to the process (106) to start the feedback control. If the determination (114) is YES, open loop control is performed (116) so that the output air-fuel ratio is set to the rich-side learning value held.
[0032]
As described above, the fuel injection control device 76 of the CNG engine 2 changes the learning control threshold value of the learning control means 82 so that the base air-fuel ratio becomes the output air-fuel ratio when the feedback region is deviated. ing. The fuel injection control device 76 of the CNG engine 2 uses the rich side learned value learned by the learning control means 82 so that the air-fuel ratio becomes the output air-fuel ratio when the throttle valve 14 is fully opened. Control open loop.
[0033]
That is, as shown in FIG. 7, the 13A gas which is the city gas supplied to the CNG engine 2 has a theoretical air-fuel ratio of around 16.8, an output air-fuel ratio of around 16.1, and an excess air ratio. λ is 0.96. In order to obtain an output air-fuel ratio with 13A gas, combustion is performed at a rich air-fuel ratio by a certain value (for example, 4%) from the theoretical air-fuel ratio.
[0034]
On the other hand, gasoline has a stoichiometric air-fuel ratio of around 14.7 and an output air-fuel ratio of around 12.5 (λ = 0.85). It will burn at the fuel ratio.
[0035]
Normally, an engine mounted on a vehicle feedback-controls the air-fuel ratio in the vicinity of the theoretical air-fuel ratio with a good catalyst purification rate in order to reduce harmful exhaust components. The output air-fuel ratio is controlled by open loop control without feedback control. Also, the learning control of the fuel injection amount is controlled so that the control center of the feedback control becomes (+) / minus (−) 0% so that a stable theoretical air-fuel ratio can be obtained as shown in FIG. is doing.
[0036]
As shown in FIG. 7, the fuel injection control device 76 of the CNG engine 2 uses the characteristic that the output air-fuel ratio of the CNG is very close to the theoretical air-fuel ratio, so that the base air-fuel ratio becomes the output air-fuel ratio on the rich side. Therefore, when the learning control threshold value is deviated from the feedback region, the base air-fuel ratio becomes the output air-fuel ratio as shown in FIG. 3B. This is set by shifting the value changed to (for example, -4%).
[0037]
As shown in FIG. 4, the learning control area is divided into zone 0 to zone 9 according to the engine speed and the intake pipe pressure. In each region (zone), a learning value M0 that is set by shifting by a value (for example, −4%) changed so that the base air-fuel ratio becomes the output air-fuel ratio when the threshold value deviates from the feedback region. ~ M9 is stored. In the zones 7, 8, and 9 near the throttle valve 14 being fully open, a feedback controlled region and an open loop controlled region (shaded portion) are mixed.
[0038]
In zones 7, 8, and 9, a learning value rich by a certain value (for example, + 4%) with respect to the theoretical air-fuel ratio is stored when feedback control is performed. When the open-loop control is determined by the full-open determination, the output air-fuel ratio is controlled by the learning value rich by this certain value (for example, + 4%).
[0039]
Thus, as shown in FIG. 2, the fuel injection control device 76 can always obtain a stable output air-fuel ratio by the learning value even in the open loop control near the fully open throttle valve 14.
[0040]
Further, the fuel injection control device 76 of the CNG engine 2 can cope with 13A gas and 12A gas which are gas fuels having different calorific values and gas compositions. The fuel composition that becomes the leanest with 12A gas is that in which methane is approximately 100%, and the theoretical air-fuel ratio is 17.2. Since the theoretical air-fuel ratio of 12A gas is about 2% leaner than the theoretical air-fuel ratio of 13A gas, if the learning control is performed richly by a certain value (for example, + 4%) so that the output air-fuel ratio becomes 13A gas, 13A Even if 12 gases are filled after using the gas, if the rich learning value is used as it is, it becomes 2% rich, so that the O2 sensor can be activated reliably and the air-fuel ratio can be normally feedback controlled. it can.
[0041]
As described above, the fuel injection control device 76 of the CNG engine 2 changes the learning control threshold value of the learning control means 82 so that the base air-fuel ratio becomes the output air-fuel ratio when the feedback region is deviated. Therefore, even when gas fuel is supplied that has a calorific value and gas composition different from the set gas fuel and the air-fuel ratio tends to be on the lean side, the learning value is learned on the rich side, The air-fuel ratio sensor can be activated by preventing leaning of the air-fuel ratio, and the fuel injection control device has a control specification dedicated to each gas fuel in order to handle two types of gas fuel with different calorific values and gas compositions There is no need to do.
[0042]
For this reason, the fuel injection control device 76 of the CNG engine 2 can also perform O2 even when gas fuel is supplied that has a calorific value and a gas composition different from the set gas fuel and the air-fuel ratio tends to be on the lean side. The inconvenience that the feedback control is not normally performed without the sensor 44 being activated can be avoided, and each gas fuel is supplied to the fuel injection control device in order to cope with two types of gas fuels having different calorific values and gas compositions. Since it is not necessary to prepare a dedicated control specification, it is possible to contribute to a reduction in design man-hours and to reduce costs.
[0043]
Further, the fuel injection control device 76 of the CNG engine 2 is configured so that the air-fuel ratio obtained from the detection signal of the O2 sensor 44 becomes the output air-fuel ratio when the fully-open condition in which the throttle valve 14 of the CNG engine 2 is fully opened is satisfied. Output air-fuel ratio control means 86 for performing open-loop control of the fuel injection amount based on the learning value learned by the learning control means 82 is provided.
[0044]
For this reason, the fuel injection control device 76 of the CNG engine 2 uses the rich learning value stored by the learning control means 82 to perform an open loop control so that an appropriate output air-fuel ratio is obtained when the throttle valve 14 is fully opened. This eliminates the need for a dedicated correction coefficient.
[0045]
In the above embodiment, the learning value is controlled by learning by shifting the value on the rich side so that the base air-fuel ratio becomes the output air-fuel ratio, but the output air-fuel ratio of CNG and the stoichiometric air-fuel ratio are very close. (For example, 4%), so that the base air-fuel ratio becomes an intermediate air-fuel ratio between the output air-fuel ratio and the stoichiometric air-fuel ratio. ) And the learning value is learned and controlled from the output air-fuel ratio to the lean side by a half value (for example, -2%), and the learning value is used as it is for feedback control and open loop control. As long as the control does not adversely affect the control, the output air-fuel ratio can be easily and stably controlled by the open loop during full-open running.
[0046]
【The invention's effect】
As described above, the fuel injection control device for the CNG engine according to the present invention also learns when gas fuel is supplied that has a calorific value and a gas composition that are different from the set gas fuel and the air-fuel ratio tends to be on the lean side. Since the value is learned to the rich side, the air-fuel ratio sensor can be prevented from being leaned and the air-fuel ratio sensor can be activated, and fuel injection control is performed to cope with two types of gas fuels with different calorific values and gas compositions There is no need to prepare control specifications for each gas fuel in the equipment.
[0047]
For this reason, the fuel injection control device of this CNG engine is an air-fuel ratio sensor even when gas fuel is supplied that has a calorific value and gas composition different from the set gas fuel and the air-fuel ratio tends to be on the lean side. Is not activated and the feedback control is not normally performed, and in order to cope with two types of gas fuels having different calorific values and gas compositions, the fuel injection control device is dedicated to each gas fuel. There is no need to prepare a control specification, which can contribute to a reduction in design man-hours and can reduce costs.
[Brief description of the drawings]
FIG. 1 is a flowchart of a fuel injection control apparatus showing an embodiment of the present invention.
FIG. 2 is a time chart of the fuel injection control device.
3A is a diagram showing a normal feedback correction coefficient, and FIG. 3B is a diagram showing a feedback correction coefficient according to the present invention.
FIG. 4 is a diagram illustrating a learning region classification based on an engine speed and an intake pipe pressure.
FIG. 5 is a diagram illustrating calculation of a learning value.
FIG. 6 is a diagram illustrating learning value data.
FIG. 7 is a diagram showing the relationship between air-fuel ratio and torque.
FIG. 8 is a schematic configuration diagram of a fuel injection control device of a CNG engine.
[Explanation of symbols]
2 CNG engine 12 Intake passage 14 Throttle valve 16 Injector 24 Exhaust passage 26 Three-way catalyst 30 Throttle sensor 34 Fully open switch 42 Rotation speed sensor 44 O2 sensor 46 Gas fuel container 50 Fuel supply pipe 60 Fuel pressure sensor 62 Fuel temperature sensor 68 Fuel filling Pipe 70 Filling port 76 Fuel injection control device 78 Control unit 80 Air-fuel ratio control means 82 Learning control means 84 Fuel supply control means 86 Output air-fuel ratio control means

Claims (1)

An air-fuel ratio sensor is provided in the exhaust passage of a CNG engine that can supply both of two types of gas fuels with different calorific values and gas compositions by an injector,
Air-fuel ratio control means for feedback-controlling the fuel injection amount with a feedback correction coefficient so that the air-fuel ratio obtained from the detection signal of the air-fuel ratio sensor when the feedback control condition is satisfied becomes the target air-fuel ratio;
Stores the value corresponding to the difference between the air-fuel ratio and the target air-fuel ratio obtained from the detection signal of the air-fuel ratio sensor during establishment of the learning condition as a learning value, the learning control for learning control to update the learning value the storage Providing means,
Fuel injection of a CNG engine provided with fuel supply control means for controlling the operation of an injector so as to inject and supply gas fuel to the CNG engine based on a value obtained by correcting the basic fuel injection amount by the feedback correction coefficient and the learning value In the control device,
The fuel injection control device for a CNG engine, wherein the learning control means performs learning control so that the base air-fuel ratio is always an output air-fuel ratio having a richer value than the stoichiometric air-fuel ratio .

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