JP2007187143A - Leakage diagnosing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage diagnosing device capable of inexpensively and accurately detecting a leak hole. <P>SOLUTION: A first temperature sensor is arranged in a fuel tank so as to not contact fuel to detect a first temperature T1, and a second temperature sensor is arranged in a position separated more from a liquid surface than the first temperature sensor to detect a second temperature T2. After passage of a stabilization time, the first temperature T1 and the second temperature T2 are detected in a state of the fuel tank and a purge device in closed systems (S22), and a temperature difference ΔT is calculated (S23). It is judged whether or not the temperature difference ΔT is a predetermined value Tth or more (S24), and if it is the predetermined value Tth or more, it is determined that there is a leak hole (S25), and if it is smaller than the predetermined value, it is determined that there is no leak hole (S26). It will be inexpensive since an expensive device such as a pump is not used, and since two temperatures T1, T2 are compared, determination accuracy will not be deteriorated due to fluctuation of a fuel tank 12 internal pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention diagnoses whether or not a leak hole having a predetermined diameter or larger exists in a fuel tank and a purge device that purges fuel gas generated by evaporation of fuel in the fuel tank into an intake passage of an internal combustion engine. The present invention relates to a leak diagnosis apparatus.

  In order to prevent the fuel gas generated from the fuel tank from leaking into the atmosphere, the fuel gas generated from the fuel tank is adsorbed to the canister, and a purge passage that communicates the canister and the intake passage of the internal combustion engine is provided. 2. Description of the Related Art A purge device that purges fuel gas adsorbed by a canister into an intake passage by using a negative pressure in the intake passage by opening a purge control valve provided is known.

  If a hole is formed in the purge device or the fuel tank, fuel gas leaks from the hole. Therefore, various devices for diagnosing whether a leak hole has occurred in the purge device or the fuel tank are known (for example, Patent Documents 1 and 2).

The apparatus of Patent Document 1 diagnoses the presence or absence of a leak hole from the pressure in the system when the inside of the sealed system is depressurized or pressurized by a pump after the fuel tank and the purge device are in a sealed system. The device of Patent Document 2 is for diagnosing the presence or absence of a leak hole by a so-called internal pressure method, and is based on a natural change in the tank internal pressure after the fuel tank and the purge device are closed. Diagnose the presence or absence of.
JP 2004-28060 A US Pat. No. 6,321,727

  In the case of the device described in Patent Document 1, although the accuracy of detecting a leak hole is high, there is a problem that the cost is high because a pump is used. On the other hand, although the apparatus described in Patent Document 2 is low in cost, there is a problem in that erroneous determination may occur because the internal pressure of the fuel tank changes depending on the ambient temperature and whether or not the fuel tends to volatilize. When fuel that tends to volatilize is used or when the ambient temperature is high, the fuel tank internal pressure tends to increase because the amount of fuel evaporation is large. Therefore, even if there is a leak hole, the internal pressure of the fuel tank becomes relatively high, so there is a possibility of erroneous determination.

  The present invention has been made based on this situation, and an object of the present invention is to provide a leak diagnosis apparatus that can detect a leak hole with low cost and high accuracy.

  In order to achieve the object, the invention according to claim 1 is directed to a fuel tank and a purge device that purges fuel gas generated by evaporation of fuel in the fuel tank into an intake passage of the internal combustion engine. A leak diagnosis device for diagnosing whether or not a leak hole has occurred, wherein the first temperature sensor is disposed in the fuel tank so as not to come into contact with the fuel and detects a first temperature, and in the fuel tank, A second temperature sensor that is disposed at a position farther from the liquid surface than the first temperature sensor and detects the second temperature, and is detected by the first temperature sensor in a state where the fuel tank and the purge device are in a closed system. And leak hole determining means for determining the presence or absence of the leak hole based on a comparison between the first temperature and the second temperature detected by the second temperature sensor.

  In the state where the evaporated fuel is purged, the fuel tank is open to the atmosphere through the canister, so that the fuel is actively evaporated. For this reason, the temperature of the gas near the liquid surface is lowered by the heat of vaporization when the fuel evaporates, but the temperature drop due to the heat of vaporization becomes smaller as the distance from the liquid surface becomes longer. Therefore, when comparing the first temperature detected by the first temperature sensor and the second temperature detected by the second temperature sensor disposed at a position farther from the liquid surface than the first temperature sensor, Since the first temperature is more greatly affected by the heat of vaporization, it is lower than the second temperature.

  On the other hand, when the fuel tank and the purge device are in a closed system, the evaporation of fuel is suppressed, so that the temperature drop due to the heat of vaporization is reduced. Therefore, the temperature difference between the first temperature and the second temperature is reduced. However, if a leak hole is generated in the fuel tank or the purge device, the fuel gas leaks from the leak hole, so that the degree to which fuel evaporation is suppressed becomes small. For this reason, the first temperature and the second temperature The temperature difference is not as small as when there are no leaks. Therefore, in the leak hole determining means, the presence or absence of the leak hole can be determined by comparing the first temperature and the second temperature in a state where the fuel tank and the purge device are in a closed system.

  In this way, when the presence or absence of a leak hole is determined, an expensive device such as a pump is not necessary, and the cost is reduced. In addition, since the presence or absence of a leak hole is determined by comparing two temperatures in the fuel tank, the determination accuracy does not decrease even if the fuel tank internal pressure changes depending on the ease of fuel volatilization or the ambient temperature. Therefore, the leak hole can be detected with high accuracy.

  Here, it is preferable that the first temperature sensor is fixed to a float floating on the fuel liquid surface as described in claim 2.

  In this way, the first temperature is always the temperature at a position where the distance from the liquid level is constant. Therefore, when the degree of fuel evaporation is the same, the first temperature is independent of the position of the liquid level. This is because the degree of temperature decrease due to heat of vaporization is constant.

  Further, the first temperature sensor is preferably as close to the liquid surface as possible without contacting the liquid surface. Specifically, as described in claim 3, the first temperature sensor is within 5 cm from the liquid surface. Preferably it is.

  Further, as described above, the temperature difference between the first temperature and the second temperature becomes large between the case where the leak hole is generated and the case where the leak hole is not generated. Therefore, according to a fourth aspect of the present invention, after the fuel tank and the purge device are set in a closed system, the leak hole determining means determines whether the first temperature and the second temperature are satisfied after a predetermined diagnosis start condition is satisfied. If the temperature difference is smaller than a predetermined value, it can be determined that no leak hole has occurred, and if the temperature difference is not less than the predetermined value, it can be determined that a leak hole has occurred.

  In addition, as the diagnosis start condition, as described in claim 5, the elapsed time after the closed system can be used as a condition, and as described in claim 6, the temperature change rate of the first temperature is It can also be a condition that it has become smaller.

  That is, the invention according to claim 5 is the leakage diagnosis apparatus according to claim 4, wherein the diagnosis start condition is a time required for the internal pressure of the fuel tank to stabilize after the fuel tank and the purge apparatus are in a closed system. A predetermined stabilization time set as follows has elapsed.

  According to a sixth aspect of the present invention, in the leak diagnostic apparatus according to the fourth aspect, the diagnosis start condition is that the change rate of the first temperature is set in advance after the fuel tank and the purge device are in a closed system. It is characterized by being smaller than the standard change rate.

  According to the fifth and sixth aspects, since the diagnosis can be started after the fuel tank internal pressure is stabilized, that is, when the fuel evaporation is minimized, it is possible to accurately determine the presence or absence of a leak hole. it can.

  The second temperature sensor preferably detects the temperature of the space formed in the fuel tank in a state where the maximum amount of fuel is supplied into the fuel tank.

  If it does in this way, the 2nd temperature detected by the 2nd temperature sensor will show the temperature of the uppermost part in a fuel tank which is hard to receive the influence of the temperature fall by vaporization heat. Therefore, since the temperature difference between the first temperature and the second temperature when a leak hole is generated can be increased, the diagnostic accuracy of the leak hole based on the temperature difference between the first temperature and the second temperature is improved.

  Hereinafter, embodiments of a leakage diagnosis apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of a purge apparatus 10 having a function as a leakage diagnosis apparatus of the present invention. The purge device 10 includes a canister 20, a connection pipe 30, a purge pipe 32, and a purge valve 34. The connection pipe 30 connects the canister 20 and the fuel tank 12.

  The canister 20 is filled with an adsorbent 22 such as activated carbon, and the connecting pipe 30 and the purge pipe 32 penetrate the upper wall of the canister 20 and the tip is located in the canister 20.

  The other end of the connection pipe 30 is located in the fuel tank 12, and the fuel gas generated in the fuel tank 12 by the connection pipe 30 is introduced into the canister 20. The fuel gas introduced into the canister 20 is adsorbed by the adsorbent 22.

  On the lower wall of the canister 20 opposite to the side to which the purge pipe 32 is connected with respect to the adsorbent 22, an air release valve 24 constituted by an electromagnetic valve is provided.

  The purge pipe 32 connects the canister 20 and an intake pipe 36 that supplies air to an engine (not shown), and the purge valve 34 is provided in the purge pipe 32. The purge valve 34 is an electromagnetic valve whose opening degree can be adjusted. When the purge valve 34 is opened and the atmosphere release valve 24 is opened, the fuel gas is released from the adsorbent 22 by the negative pressure of the intake pipe 36 and mixed with the air introduced from the atmosphere release valve 24. Then, it is purged (released) into the intake pipe 36.

  A fuel level sensor 40 for measuring the fuel in the fuel tank 12 is provided in the fuel tank 12. The fuel level sensor 40 includes a float 42 that floats on the fuel level and a liquid level position detector 44 that detects the height position of the float 42, that is, the fuel level position. The liquid level position detected by the liquid level position detector 44 is supplied to the ECU 50.

  A first temperature sensor 46 is fixed to the upper surface of the float 42 that does not contact the fuel. The first temperature sensor 46 is fixed so as to be within 5 cm from the liquid level, and detects the gas temperature in the region closest to the liquid level. A second temperature sensor 48 is fixed to the upper wall of the fuel tank 12. The length of the second temperature sensor 48 protruding into the fuel tank 12 is a length that does not contact the fuel in a normal fuel full state, that is, a state in which the maximum amount of fuel is supplied. The gas temperature is detected. The first temperature T1 detected by the first temperature sensor 46 and the second temperature T2 detected by the second temperature sensor 48 are supplied to the ECU 50.

  The ECU 50 is a so-called computer including a CPU, a ROM, a RAM, and the like (not shown). The ECU 50 determines whether or not to perform the purge control based on the state of the ignition switch, the driving state of the engine, and the like, and opens the purge valve 34 and the atmosphere release valve 24 when performing the purge control. As a result, the fuel gas adsorbed on the adsorbent 22 of the canister 20 is purged to the intake pipe 36.

  The ECU 50 also performs leak check control for diagnosing whether or not a leak hole having a predetermined diameter or more has occurred in the fuel tank 12 and the purge device 10. This leak check control corresponds to leak hole determination means.

  FIG. 2 is a flowchart showing the contents of the leak check control. The routine shown in FIG. 2 is repeatedly executed at a predetermined short period when the ignition switch is OFF. Note that when the ignition switch is turned off, the purge valve 34 and the atmosphere release valve 24 are closed.

  First, in step S21, it is determined whether a diagnosis start condition is satisfied. That is, it is determined whether or not the elapsed time after the ignition switch is turned off has passed a preset stabilization time. This stabilization time is determined based on experiments as the time required for the internal pressure of the fuel tank 12 to stabilize, and is, for example, 3 to 5 hours. If step S21 is negative, this routine is terminated.

  On the other hand, if step S21 is affirmative, the first temperature T1 and the second temperature T2 are detected in step S22. In step S23, a temperature difference ΔT (T2−T1) is calculated.

  In subsequent step S24, it is determined whether or not the temperature difference ΔT calculated in step S23 is equal to or larger than a predetermined value Tth set in advance. If step S24 is affirmative, that is, if the temperature difference ΔT is greater than or equal to the predetermined value Tth, the process proceeds to step S25, where it is determined that there is a leak hole. On the other hand, if step S24 is negative, that is, if the temperature difference ΔT is smaller than the predetermined value Tth, the process proceeds to step S26 and it is determined that there is no leak hole.

  FIG. 3 is a diagram illustrating a change in the first temperature T1 when the leak hole is generated and when the leak hole is not generated. Before the time t0, the purge is being performed, and in this state, the atmosphere release valve 24 is in an open state, so that the fuel is actively evaporated in the fuel tank 20. Therefore, the first temperature T1, which is greatly affected by the temperature decrease due to the heat of vaporization, is lower than the second temperature T2, which is less affected by the temperature decrease due to the heat of vaporization.

  The time point t0 is a time point when the ignition switch is turned off. At this time point, the purge valve 34 and the atmosphere release valve 24 are closed. When the atmosphere release valve 24 and the purge valve 34 are closed, the fuel tank 12 and the purge device 10 become a closed system, so that the pressure gradually increases, and the evaporation of the fuel gradually decreases in the fuel tank 12 accordingly. As the evaporation of fuel decreases, the heat of vaporization also decreases, so the first temperature T1, which is greatly affected by the heat of vaporization, gradually increases. When the pressure in the fuel tank 12 is stabilized, the first temperature T1 is also substantially constant.

  A time point t1 in FIG. 3 indicates a time point when the stabilization time has elapsed from a time point t0. After the time point t1, the first temperature T1 is a substantially constant value. The first temperature T1 after the time t1 is relatively close to the second temperature T2, as indicated by a solid line, when no leak hole is generated.

  However, when a leak hole is generated, fuel gas leaks from the leak hole, and thus the evaporation of fuel continues even after the purge valve 34 and the atmosphere release valve 24 are closed. The first temperature T1 does not rise to the vicinity of the second temperature T2, and the temperature difference ΔT becomes relatively large. Therefore, the presence or absence of a leak hole can be determined based on the temperature difference ΔT.

  As described above, according to the present embodiment described above, since an expensive device such as a pump is not used, the cost is reduced. Moreover, since the presence or absence of a leak hole is determined by comparing the two temperatures T1 and T2 in the fuel tank 12, the determination accuracy is lowered even if the internal pressure of the fuel tank 12 changes depending on the ease of volatilization of the fuel or the ambient temperature. do not do. Therefore, the leak hole can be detected with high accuracy.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following embodiment is also contained in the technical scope of this invention, and also the summary other than the following is also included. Various modifications can be made without departing from the scope.

  For example, in the above-described embodiment, the presence / absence of a leak hole is determined based on the temperature difference ΔT between the first temperature T1 and the second temperature T2, but the temperature ratio between the first temperature T1 and the second temperature T2 is determined. The presence or absence of a leak hole may be determined based on this.

  In the above-described embodiment, the first temperature sensor 46 is fixed to the float 42 of the fuel level sensor 40, but may be fixed to the fuel tank 12. In addition to the float 42 of the fuel level sensor 40, a float for the first temperature sensor 46 may be provided. Further, the first temperature sensor 46 can be moved in the vertical direction in the fuel tank 12 by a motor or the like, and the position of the first temperature sensor 46 is controlled based on the liquid level position detected by the fuel level sensor 40. You may do it.

  Further, the position of the first temperature sensor 46 from the liquid surface does not need to be within 5 cm, and the position from the liquid surface may be 5 cm or more as long as it is closer to the liquid surface than the second temperature sensor 48.

  Further, in the above-described embodiment, step S22 and the subsequent steps are performed assuming that the pressure in the fuel tank 12 is stabilized when the elapsed time since the fuel tank 12 and the purge device 10 are set to the closed system has passed the stabilization time. The presence or absence of leak holes was determined. However, the temperature change rate of the first temperature T1 may be calculated sequentially, and step S22 and subsequent steps may be performed when the change rate becomes smaller than the reference change rate.

It is a schematic diagram which shows the structure of the purge apparatus 10 provided with the function as a leak diagnostic apparatus of this invention. It is a flowchart which shows the content of leak check control. It is a figure which illustrates the change of 1st temperature T1 when the case where the leak hole has arisen and the case where it does not arise.

Explanation of symbols

10: Purge device (leakage diagnostic device)
12: Fuel tank 20: Canister 42: Float 46: First temperature sensor 48: Second temperature sensor 50: ECU (leak hole determination means)

Claims (7)

A leakage diagnosis device for diagnosing whether or not a leak hole having a predetermined diameter or more is formed in a fuel tank and a purge device that purges fuel gas generated by evaporation of fuel in the fuel tank into an intake passage of an internal combustion engine There,
A first temperature sensor disposed in the fuel tank so as not to contact the fuel and detecting a first temperature;
A second temperature sensor disposed in a position farther from the liquid surface than the first temperature sensor in the fuel tank to detect a second temperature;
Based on the comparison between the first temperature detected by the first temperature sensor and the second temperature detected by the second temperature sensor in a state where the fuel tank and the purge device are in a closed system, the leakage hole A leak diagnosis apparatus comprising: a leak hole determining means for determining presence or absence.   The leak diagnosis apparatus according to claim 1, wherein the first temperature sensor is fixed to a float floating on a fuel liquid level.   The leak diagnosis apparatus according to claim 1, wherein the first temperature sensor is within 5 cm from the liquid level.   When the fuel tank and the purge device are in a closed system, and after a predetermined diagnosis start condition is satisfied, the leak hole determination unit is configured such that a temperature difference between the first temperature and the second temperature is smaller than a predetermined value. The leakage according to any one of claims 1 to 3, wherein it is determined that no leak hole has occurred, and if the temperature difference is not less than a predetermined value, it is determined that a leak hole has occurred. Diagnostic device.   The diagnosis start condition is that a predetermined stabilization time set as a time necessary for the internal pressure of the fuel tank to stabilize is passed after the fuel tank and the purge device are closed. Item 5. The leakage diagnosis device according to Item 4.   5. The diagnosis start condition is that after the fuel tank and the purge device are in a closed system, the change rate of the first temperature is smaller than a preset reference change rate. The leakage diagnosis apparatus described.   The said 2nd temperature sensor detects the temperature of the space formed in a fuel tank in the state which supplied the maximum amount of fuel in the said fuel tank, The one of Claims 1 thru | or 6 characterized by the above-mentioned. The leak diagnosis device according to 1.

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