JPH04262047A - Failure detecting device of evaporative fuel control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately judge the failure of a device, even if there is a dispersion in the characteristic of a fuel density sensor, by judging the presence of failure of the device by comparing the difference between the detected value of the fuel density sensor provided to an evaporative fuel supply passage or inside a canister and that of the fuel density sensor at the time before and after the command for opening a purge control valve is given with a prescribed value. CONSTITUTION:Between a canister 11 for adsorbedly collecting evaporative fuel and an intake pipe 3, a fuel density sensor 17 is provided, and a failure judging means by which the presence of failure of a device is judged by comparing the difference in the detected values of the fuel density sensor 17 at the time before and after the opening command of a purge control valve 16 for controlling the supply of evaporative fuel is given with a prescribed value.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to a failure detection device for determining the presence or absence of a failure in an engine vaporized fuel control device that controls the supply of vaporized fuel to an internal combustion engine (hereinafter abbreviated as the engine). It is related to.

0002

2. Description of the Related Art Generally, in automobile engines, measures have been taken to prevent air pollution caused by fuel evaporative gas containing mainly harmful HC components. In this system, evaporated fuel generated in a fuel tank or the like is adsorbed and collected by a canister, and is supplied to the engine's intake system through an evaporated fuel supply passage provided between the canister and the engine's intake system.

Furthermore, if this evaporated fuel is unconditionally supplied to the intake system, the air-fuel ratio of the fuel-air mixture will vary greatly, resulting in deterioration of engine operating performance. For this reason, a purge control valve is provided in the vaporized fuel supply passage, and the opening and closing of the purge control valve is controlled by a purge control command from a control device according to the operating conditions of the engine. In this case, the engine fuel vapor control device is configured to open the purge control valve and supply vaporized fuel to the intake system only under operating conditions where there is no problem with the air-fuel ratio even if vaporized fuel is supplied to the intake system. .

[0004] Furthermore, in view of the strengthening of air pollution prevention in recent years, for example, when a failure occurs in the evaporative fuel control system for an engine, such as deterioration or damage to the evaporative fuel supply passage, deterioration or damage to the canister, or failure of the purge control valve. In order to prevent evaporated fuel from leaking into the atmosphere, this fault can be detected and alerted at an early stage.
It is proposed to encourage repair of the malfunctioning part.

The above failure detection method involves detecting the fuel concentration in the vaporized fuel supply passage downstream of the purge control valve using a fuel concentration sensor, and receiving a purge control command from the control device to open the purge control valve. Under these conditions, a method is usually used in which it is determined that the fuel concentration is normal when it is above a predetermined value, and that it is determined to be malfunctioning when it is below the predetermined value.

[0006] As a fuel concentration sensor normally used in the above-mentioned failure detection device, for example, a thin film resistor is formed by dispersing conductive particles in a polymeric substance, and fuel vapor infiltrates the thin film resistor. An example of this is a fuel concentration sensor that causes a change in resistance due to the swelling effect caused by this. FIG. 3 shows the characteristics of this type of fuel concentration sensor, and the detection characteristics of each sensor vary greatly in resistance value depending on the fuel concentration.

[0007]

[Problems to be Solved by the Invention] Since the failure detection device of the conventional evaporative fuel control device for engines is as described above, the resistance value of a fuel concentration sensor having the characteristic a in FIG. As the resistance value at 0.5% fuel concentration of the fuel concentration sensor having the characteristic b in FIG. It is difficult to distinguish, for example, between 0% and 0.5% fuel concentration by comparing the output of the fuel concentration sensor and the output of the fuel concentration sensor, resulting in problems such as failure detection being impossible.

The present invention has been made to solve the above-mentioned problems, and it is possible to accurately determine the failure of an evaporative fuel control system for an engine even if there are variations in the characteristics of the fuel concentration sensor. The purpose is to obtain a detection device.

[0009]

[Means for Solving the Problems] A failure detection device for an evaporative fuel control device for an engine according to the present invention controls the supply of evaporative fuel by opening and closing an evaporative fuel supply passage connecting a canister and an intake pipe with a purge control valve. In a device that operates, the difference in detected values between a fuel concentration sensor installed in the evaporative fuel supply passage or canister and the fuel concentration sensor before and after the purge control valve is commanded to open is compared with a predetermined value to determine whether or not there is a malfunction in the device. A failure determination means is provided.

0010

[Operation] In the failure detection device for an engine evaporative fuel control device according to the present invention, the concentration change of the evaporated fuel at the detection unit before and after the command to open the purge control valve is influenced by the presence or absence of a failure in the evaporative fuel control device. Therefore, the concentration change is detected by the fuel concentration sensor, and the difference in the detected concentration value representing the concentration change is compared with a predetermined value, and the presence or absence of a failure is determined by the failure determination means.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an engine section including a failure detection device for an evaporative fuel control device for an engine according to an embodiment of the present invention. In Fig. 1, 1 is an engine, and 2 is an input interface section for inputting analog input signals and digital input signals, an arithmetic processing section, a driver section for driving various loads, etc. Ignition system (not shown)
3 is an intake pipe of the engine 1.

Reference numeral 4 denotes an air flow meter provided in the intake pipe 3 for measuring the intake air amount of the engine 1, and for example, a heat-sensitive flow meter is used. 5 is a throttle opening sensor that detects the opening of a throttle valve 51 that adjusts the opening of the intake pipe 3; 6 is an intake pipe pressure sensor that detects the pressure downstream of the throttle valve 51 in the intake pipe 3;

7 is an O2 sensor for detecting the oxygen concentration in the exhaust gas of the engine 1; 8 is a rotation sensor for detecting the rotational speed of the engine 1; 9 is a fuel injection valve for injecting fuel into the intake pipe 3. . The control unit 2 is connected to components 4 to 9, detects the operating state of the engine 1 based on detection signals from sensors 4 to 8, and optimizes the air-fuel ratio according to the operating state. The fuel injection valve 9 is then driven to control the fuel system, and the ignition system is also controlled so that the ignition timing is optimized.

10 is a fuel tank filled with fuel, and 11 is an adsorbent 1 such as activated carbon inside to adsorb and collect evaporated fuel.
2 is a filled canister. 13 is fuel tank 1
The vaporized fuel generated by vaporization inside the canister 11
This is an evaporated fuel introduction passage for introducing evaporated fuel into the canister 11, and the evaporated fuel generated inside the fuel tank 10 after the engine 1 stops operating is introduced into the canister 11 and is adsorbed and collected.

Further, the intake pipe 3 section upstream of the fuel injection valve 9 and downstream of the throttle valve 51 and the canister 11 are connected by vaporized fuel supply passages 14 and 15, and a purge control valve is connected between the fuel supply passages 14 and 15. 16 are provided. The purge control valve 16 opens and closes between the vaporized fuel supply passages 14 and 15 in response to an opening/closing command from the control unit 2.
The valve opens when the vaporized fuel can be supplied (hereinafter referred to as purge-on conditions), and the vaporized fuel adsorbed and collected in the canister 11 is supplied into the intake pipe 3 by the negative pressure in the intake pipe 3. do.

17 is a purge control valve 16 and an intake pipe 3.
A fuel concentration sensor provided in the fuel vapor supply passage 15 connecting the fuel vapor supply passage 15 detects the concentration of the fuel vapor in the fuel vapor supply passage 15, and changes the resistance value according to this concentration. This fuel concentration sensor 17 is connected to the control unit 2 and outputs a signal to the control unit 2 according to the detected fuel concentration. 18 is a one-way valve that allows evaporated fuel to pass only from the fuel tank 10 to the canister 11.

The control unit 2 is constructed so that it can simultaneously operate an engine evaporative fuel control system and a failure detection system for this system.

FIG. 2 is a flowchart showing the failure detection operation of a failure detection device for an engine evaporative fuel control system according to an embodiment of the present invention, which is stored in the control unit 2 as a control program.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2. First, in step S1, the control unit 2 detects the operating state of the engine 1 based on signals from the air flow meter 4, throttle opening sensor 5, intake pipe pressure sensor 6, O2 sensor 7, rotation sensor 8, etc., and turns on the purge. Determine whether the condition is met. If the condition is not purge-on, the control unit 2 instructs the purge control valve 16 to close in step S2.

If it is determined in step S1 that the purge-on condition is satisfied, the control unit 2 first reads and stores the detection value ROFF of the fuel concentration sensor 17 before the command to open the purge control valve 16, and then in step S3 In step S4, a command is given to open the purge control valve 16.

If the engine fuel evaporation system is normal, the purge control valve 16 opens in response to an opening command from the control valve 16 to communicate the evaporated fuel supply passages 14 and 15, and the canister 11 from the fuel tank 10 through the evaporated fuel introduction passage 13. The evaporated fuel adsorbed and collected by the adsorbent 12 in the intake pipe 3 is sufficiently sucked into the intake pipe 3 by the negative pressure of the intake pipe 3. Therefore, in this case, a predetermined amount of evaporated fuel reaches the fuel concentration sensor 17.

If the engine fuel evaporator is malfunctioning, the purge control valve 16 will not open even if the purge control valve 16 is commanded to open, or even if it opens, a predetermined amount of evaporated fuel will be removed from the canister 11 due to a malfunction elsewhere. Therefore, a predetermined amount of evaporated fuel does not reach the fuel concentration sensor 17.

After issuing a command to open the purge control valve 16, the control unit 2 reads and stores the detected value RON of the fuel concentration sensor 17 again in step S5.

Next, in step S6, the control unit 2 calculates the difference (RON-ROFF) between the detected values of the fuel concentration sensor 17 before and after the command to open the purge control valve 16, and in the next step S7, this detected value is calculated. Difference in value (RON
-ROFF) is larger than a predetermined value that is a threshold for failure determination.

[0025] This predetermined value is determined from the value at which, when the engine evaporative fuel control system is normal, the difference in the detected value of the fuel concentration sensor before and after the command to open the purge control valve is the minimum, taking into account the variation in its characteristics. It is set to a small value. Further, this predetermined value is set to be greater than or equal to the value at which the difference between the detected values of the fuel concentration sensors before and after the command to open the purge control valve is maximized when the engine evaporative fuel control device fails.

Failure of the engine evaporative fuel control device, such as damage to the evaporative fuel introduction passage 13 or evaporative fuel supply passages 14 and 15, damage to the canister 11, deterioration of the adsorbent 12, malfunction of the purge control valve 16, etc. When this occurs, the following will occur. Even though the control signal from the control unit 2 instructs the purge control valve 16 to open, a predetermined amount of evaporated fuel does not reach the fuel concentration sensor 17. Therefore, the difference (RON-ROFF) between the detected values of the fuel concentration sensor 17 before and after the command to open the purge control valve 16 does not exceed the predetermined value, and the control unit 2 makes a negative determination in step S7 and proceeds to step S8. It is determined that the device has failed.

If there is no failure in the engine evaporative fuel control device and its operation is normal, a predetermined amount of evaporated fuel reaches the fuel concentration sensor 17 after the purge control valve 16 is commanded to open. Therefore, the difference (RON-ROFF) between the detected values of the fuel concentration sensor before and after the command to open the purge control valve 16 becomes equal to or greater than the predetermined value, and the control unit 2 makes an affirmative determination in step S7, and the control unit 2 makes an affirmative determination in step S9. It is determined that there is no failure.

The series of processing ends after processing any one of steps S2, S8, and S9.

In addition to the embodiments described above, the fuel concentration sensor 17 may be disposed, for example, in the vaporized fuel supply passage 14 between the purge control valve 16 and the canister 11, or in the canister 1.
It may be arranged in the canister 11 to detect the concentration of evaporated fuel in the canister 11. In this case, if the engine evaporative fuel control device is normal, the fuel concentration in the detection section will decrease when the purge control valve 16 opens, so the difference in the detected value of the fuel concentration sensor before and after the purge control valve is opened (ROFF -RON) is determined to be normal when it is above a predetermined value, and abnormal when it is below.

[0030]

As described above, according to the present invention, the change in the detected value of the fuel concentration sensor before and after the command to open the purge control valve is determined, and compared with a predetermined threshold value for failure determination, the change in the detected value of the fuel concentration sensor is determined. Since the configuration is configured to determine whether or not there is a failure in the control device, there is an effect that failure can be determined accurately even if a type of fuel concentration sensor having a large variation in individual characteristics is used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an engine section including a failure detection device for an engine evaporative fuel control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation example of failure detection of the control unit in FIG. 1;

FIG. 3 is a characteristic diagram of a fuel concentration sensor.

[Explanation of symbols]

1 Institution 2 Control unit 3 Intake pipe 10 Fuel tank 11 Canister 12 Adsorbent 13 Evaporative fuel introduction passage 14, 15 Evaporative fuel supply passage 16 Purge control valve 17 Fuel concentration sensor

Claims (1)

[Claims] Claim 1: A canister that adsorbs and collects evaporated fuel generated in a fuel tank, etc., and a purge control valve that opens and closes an evaporated fuel supply passage that connects the canister and an intake pipe of an internal combustion engine. In the evaporated fuel control device that controls the supply of evaporated fuel from the canister to the intake pipe of the internal combustion engine by opening and closing a valve, a fuel concentration device is provided in the evaporated fuel supply passage or in the canister and detects the concentration of the evaporated fuel. and a failure determining means for determining whether or not there is a failure in the evaporated fuel control device by comparing the difference between the detected value of the sensor and the fuel concentration sensor before and after the command to open the purge control valve and a predetermined value. A failure detection device for an evaporative fuel control device for an internal combustion engine, characterized by: