JP2884463B2 - Fault diagnosis device for compressed natural gas engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine using compressed natural gas (compressed natural gas (hereinafter abbreviated as CNG)) as a fuel, and more particularly to an air-fuel ratio sensor provided in an air-fuel ratio control device. The present invention relates to a device for diagnosing a failure.

[0002]

2. Description of the Related Art Generally, as one of the methods for judging an abnormality of an analog input signal of a control device, a method of judging an abnormality when an input voltage falls below or above a physical detection range is adopted.

[0003]

Conventionally, when this method is employed to diagnose a failure of an air-fuel ratio sensor provided in an air-fuel ratio control device of an engine using CNG as fuel, There is a problem as follows. That is,
The failure diagnostic device employed in the CNG engine includes an upper limit determining unit that determines whether a voltage signal output from the air-fuel ratio sensor has exceeded an upper limit of a predetermined range, and a lower limit that determines whether a voltage signal has fallen below a lower limit of the predetermined range. A determination means and an abnormality determination means for determining that the air-fuel ratio sensor is abnormal when it is determined that the voltage signal has exceeded the upper limit of the predetermined range or when it has been determined that the voltage signal has fallen below the lower limit.

The CNG engine has a structure in which a mixer as a fuel supply means and a throttle valve are connected from a gas cylinder as a fuel supply source via a fuel cut valve (see Japanese Utility Model Application No. 4-57564). In a CNG engine, when the fuel cut valve is operated to perform a fuel cut, the air-fuel ratio sensor detects pure air, and is output from the air-fuel ratio sensor by the configuration of the failure diagnosis device described above. Since the voltage signal exceeds the upper limit of the predetermined range, it is erroneously diagnosed that the air-fuel ratio sensor is abnormal.

In view of the above problems, the present invention has been made to avoid unnecessary failure diagnosis in a device for diagnosing a failure of an air-fuel ratio sensor provided in an air-fuel ratio control device of a CNG engine. With the goal.

[0006]

Therefore, as shown in FIG. 1, the present invention provides a voltage signal output from an air-fuel ratio sensor provided in an air-fuel ratio control device of an engine using compressed natural gas as fuel. Upper limit determining means for determining whether or not exceeds the upper limit of the predetermined range, lower limit determining means for determining whether or not below the lower limit of the predetermined range, and when it is determined that the voltage signal has exceeded the upper limit of the predetermined range or When it is determined that the lower limit is less than the lower limit, abnormality determination means for determining that the air-fuel ratio sensor is abnormal,
Means for detecting a fuel cut operation of a fuel cut valve provided between the fuel supply source and the fuel supply means, and prohibition means for prohibiting the determination by the upper limit determination means when the fuel cut operation is detected by the means. Is provided.

[0007]

In this configuration, when the fuel cut operation of the fuel cut valve is detected, the determination by the upper limit determining means is prohibited, so that the voltage signal output from the air-fuel ratio sensor is reduced by the fuel cut operation to the upper limit of the predetermined range. When the value exceeds the limit, it is not possible to erroneously determine that the air-fuel ratio sensor is abnormal, and unnecessary trouble diagnosis can be avoided.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. 2, an exhaust manifold 2 is attached to an engine 1. An exhaust pipe 6 is provided on the exhaust manifold through an air-fuel ratio sensor 3, an exhaust shutter 4, and a muffler 5 provided in an air-fuel ratio control device of the engine. Is provided. The exhaust shutter 4 is driven by an air cylinder device 7, and an air reservoir (not shown) is connected to the air cylinder device 7 via an exhaust brake valve 8. A main throttle valve 10 interlocked with an accelerator pedal is provided on an intake manifold 9 forming an intake air-fuel mixture passage.
And a sub-throttle valve 12 and a mixer 13 which are interposed in series with the main throttle valve 10 and driven independently of the main throttle valve 10 by a motor 11 as driving means. An intake pipe 14 constituting a passage is provided, and an air duct 15 is attached to the intake pipe 14, and an air cleaner 16 is attached to the air duct 15.
Is attached. A bypass passage 17 that bypasses the main throttle valve 10 is provided in the intake pipe 14, and an idle speed control valve 18 is interposed in the bypass passage 17. Intake pipe 14 and air duct 1 between intake manifold 9 and main throttle valve 10
5, an intake bypass pipe 19 is provided, and an intake control valve 20 is interposed in the intake bypass pipe 19. The mixer 13 is provided with a venturi 21 provided in the intake pipe 14, an electronic fuel control valve 22 whose driving is controlled by a duty-controlled feedback solenoid, a fuel cut valve 23, and an orifice 24 for adjusting the flow rate of the introduced fuel. Have been. A fuel supply pipe 26 from a regulator 25 connected to a CNG cylinder (not shown) is branched into two, and one branch pipe 26A is connected to the fuel cut valve 2.
3 and the other branch pipe 26 </ b> B is connected to the electronic fuel control valve 22.

The intake control valve 20 and the fuel cut valve 23 are driven by vacuum air, respectively.
0 and the vacuum air pipe 27A to the fuel cut valve 23,
27B are respectively connected. This vacuum pipe 27A,
Solenoids 28A and 28B for opening and closing the respective vacuum pipes 27A and 27B are interposed in 27B. on the other hand,
The main throttle valve 10 is provided with an idle switch 29 that is turned on when the main throttle valve 10 is fully closed.

[0010] A crank angle sensor 30 is provided as engine speed detecting means. Next, detection signals output from the air-fuel ratio sensor 3, the crank angle sensor 30, and the idle switch 29 are input to the control unit 31. Also, from the control unit 31, the exhaust brake valve 8, the motor 11,
Control signals are output to the solenoids 28A and 28B, the electronic fuel control valve 22, and the idle speed control valve 18.

As shown in FIG. 3, the output signal from the air-fuel ratio sensor 3 is input to an air-fuel ratio-oxygen concentration conversion amplifier 32 in a control unit 31, and the output signal from the conversion amplifier 32 is A / D converter 33. Here, the control unit 31 is equipped with air-fuel ratio feedback control means for controlling the electronic fuel control valve 22 based on the air-fuel ratio detected by the air-fuel ratio sensor 3 to perform air-fuel ratio feedback control in software. .

The control unit 31 receives detection signals output from a crank angle sensor 30, an idle switch 29, a shift position detection sensor for a transmission (not shown), and an exhaust brake switch (not shown) for operating the exhaust brake valve 8. Fuel cut valve 2
The fuel cut valve control means for controlling the operation of No. 3 is provided by software.

Further, the control unit 31 has an upper limit determining means for determining whether the voltage signal output from the air-fuel ratio sensor 3 has exceeded the upper limit of the predetermined range, and a determination whether or not the voltage signal has fallen below the lower limit of the predetermined range. An abnormality determining means for determining that the air-fuel ratio sensor 3 is abnormal when it is determined that the voltage signal has exceeded the upper limit of the predetermined range or when it has been determined that the voltage signal has fallen below the lower limit. Open-loop control means for stopping the air-fuel ratio feedback control by the air-fuel ratio sensor 3 and controlling the electronic fuel control valve 22 at a constant duty ratio (open-loop control) when it is determined to be abnormal; Means for detecting the fuel cut operation of the fuel cut valve 23, and prohibiting means for prohibiting the determination by the upper limit determining means when the fuel cut operation is detected by the means. There has been equipped software.

The control contents of the control unit 31 will be described with reference to the flowcharts of FIGS. FIG. 4 is a flowchart for explaining the control contents of the fuel cut valve 23. In step 1 (abbreviated as S1 in the figure, the same applies hereinafter), it is determined whether or not the engine speed N has exceeded the maximum speed _NMAX. It is determined, and if it exceeds, the routine proceeds to step 2 where the fuel cut valve 23 is operated to execute the fuel cut. If not, go to step 3. In step 3, it is determined whether or not the shift position of the transmission is neutral. If the shift position is neutral, the process proceeds to step 4, in which the operation of the fuel cut valve 23 is stopped to stop fuel cut. If it is not neutral, the process proceeds to step 5 to determine whether or not the idle switch 29 is ON. If it is ON, the process proceeds to step 6; Stop cutting. In step 6, it is determined whether the engine rotational speed N exceeds the first predetermined rotational speed N _1, exceeds it, the process proceeds to Step 2, to perform a fuel cut as described above. If not, go to step 7. In step 7, it is determined whether the engine rotational speed N exceeds a second predetermined rotational speed N _2, exceeds it,
Proceed to step 8; if not, proceed to step 4 to stop fuel cut as described above. In step 8, it is determined whether or not the exhaust brake switch is ON. If the switch is ON, the process proceeds to step 2 and the fuel cut is executed. I do.

According to the flowchart, the fuel cut is performed under the following conditions (1) to (3). (1) When the engine speed exceeds the maximum speed _NMAX . (2) the engine rotational speed is the first predetermined rotational speed N ₁ or less, and the idle switch 29 is in ON, when the transmission is not in neutral.

[0016] (3) the engine rotational speed is the second predetermined rotational speed N ₂ or less, and the idle switch 29 is in ON, the transmission is not neutral, when the exhaust brake switch is ON. Note that the relationship between the maximum rotation speed N _MAX , the first predetermined rotation speed N _1, and the second predetermined rotation speed N ₂ is N ₂ <N ₁ <N _MAX . Further, while the fuel cut is being performed, the electronic fuel control valve 22 that performs the air-fuel ratio feedback control based on the air-fuel ratio detected by the air-fuel ratio sensor 3 necessarily supplies zero fuel.

FIG. 5 is a flow chart for explaining the control for determining the abnormality of the air-fuel ratio sensor 3. In step 11, it is determined whether or not the fuel cut valve 23 is operating. If the operation is not being performed (the fuel cut is released), the process proceeds to step 13. In this step 13, it is determined whether or not a fixed time has elapsed after the fuel cut is released, and if the fixed time has elapsed, the process proceeds to step 14. If the fixed time has not elapsed, the process proceeds to step 12. In step 14, the air-fuel ratio sensor 3
, That is, the voltage signal output from the air-fuel ratio sensor 3 exceeds the upper limit of the predetermined range (control range) shown in FIG. When it is determined that the voltage signal has exceeded the upper limit of the predetermined range, the process proceeds to step 15, where it is determined that the air-fuel ratio sensor 3 is abnormal, and the process proceeds to step 12. When it is determined that the voltage signal does not exceed the upper limit of the predetermined range, the process proceeds to step 12. In step 12, the voltage signal output from the air-fuel ratio sensor 3 is changed to a predetermined range (control range) shown in FIG.
It is determined whether the value is below the lower limit. If it is determined that the voltage signal has fallen below the lower limit of the predetermined range, step 1
Proceeding to 6, it is determined that the air-fuel ratio sensor 3 is abnormal. The process ends when it is determined that the voltage signal does not fall below the lower limit of the predetermined range.

FIG. 6 is a flowchart for explaining the details of the air-fuel ratio control when the air-fuel ratio sensor 3 is determined to be abnormal. In step 21, it is determined whether the air-fuel ratio sensor 3 is abnormal. Then, the air-fuel ratio feedback control by the air-fuel ratio sensor 3 is executed. If there is an abnormality, the process proceeds to step 23, where the air-fuel ratio feedback control by the air-fuel ratio sensor 3 is stopped, and
2 is controlled at a constant duty ratio (open loop control).

According to this configuration, when the fuel cut operation of the fuel cut valve 23 is detected, the determination by the upper limit determining means is prohibited, so that the voltage signal output from the air-fuel ratio sensor 3 is determined by the fuel cut operation. When the upper limit of the range is exceeded, it is not possible to erroneously determine that the air-fuel ratio sensor 3 is abnormal, thereby avoiding unnecessary failure diagnosis. As described above, the present invention has been described with reference to the specific embodiments. However, the present invention is not limited to these embodiments. It should be noted that various changes and modifications can be made without departing from the scope.

[0020]

As described above, according to the failure diagnosis apparatus for a compressed natural gas engine of the present invention, when it is determined that the voltage signal output from the air-fuel ratio sensor has exceeded the upper limit of the predetermined range or has fallen below the lower limit. When it is determined that the air-fuel ratio sensor is abnormal, the configuration is such that the determination by the upper limit determining means is prohibited when the fuel cut operation of the fuel cut valve is detected. When the fuel cut is performed, the air-fuel ratio sensor detects pure air, so that there is no erroneous diagnosis that the air-fuel ratio sensor is abnormal, and the usefulness of avoiding unnecessary failure diagnosis increases. Things.

[Brief description of the drawings]

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a system diagram showing an embodiment of a failure diagnosis device for a compressed natural gas engine according to the present invention.

FIG. 3 is a diagram showing an output structure of an air-fuel ratio sensor in the embodiment.

FIG. 4 is a flowchart illustrating control contents of the embodiment.

FIG. 5 is a flowchart illustrating control contents of the embodiment.

FIG. 6 is a flowchart illustrating control contents of the embodiment.

FIG. 7 is a diagram for explaining a control range of the air-fuel ratio sensor in the embodiment.

[Explanation of symbols]

 Reference Signs List 1 engine 3 air-fuel ratio sensor 23 fuel cut valve 31 control unit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Takada 1-chome, 1-chome, Ageo-shi, Saitama Nissan Diesel Industry Co., Ltd. (72) Inventor Nobuo Hamasaki 1-1-chome, 1-chome, Ageo-shi, Saitama Nissan Diesel (56) References JP-A-4-69565 (JP, A) JP-A-3-88933 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02M 21/02 F02D 41/14

Claims (1)

(57) [Claims] An upper limit determining means for determining whether a voltage signal output from an air / fuel ratio sensor provided in an air / fuel ratio control device of an engine using compressed natural gas as fuel has exceeded an upper limit of a predetermined range; A lower limit determining means for determining whether or not a lower limit of a predetermined range is exceeded; and determining that the air-fuel ratio sensor is abnormal when it is determined that the voltage signal has exceeded the upper limit of the predetermined range or has been determined to be lower than the lower limit. An abnormality determining means, comprising: a means for detecting a fuel cut operation of a fuel cut valve provided between the fuel supply source and the fuel supply means; and a fuel cut operation performed by the means. A failure diagnosis device for a compressed natural gas engine, further comprising: a prohibition unit that prohibits the determination by the upper limit determination unit when detected.