Apparatus and method for diagnosing faults of fuel vapor...

Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system

Reexamination Certificate

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Reexamination Certificate

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06321728

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to technology for diagnosing the presence of faults (fuel vapor leaks) in a fuel vapor treatment unit of an internal combustion engine, and in particular to technology for preventing erroneous diagnosis and increasing diagnosis accuracy.
2. Description of the Related Art
With conventional fuel vapor treatment units for internal combustion engines, diffusion of fuel vapor into the atmosphere is prevented by temporarily adsorbing fuel vapor generated in the fuel tank etc. into an adsorption unit (canister), and then, under predetermined engine operating conditions, de-adsorbing the adsorbed fuel vapor and mixing this with purge air, and drawing the purge mixture into an engine intake system, while controlling the flow of purge mixture with a purge control valve (refer to Japanese Unexamined Patent Publication No. 5-215020).
With the above units however, if a crack occurs along the fuel vapor piping, or a fault occurs in a seal at a fuel vapor piping connection, then the fuel vapor will diffuse into the atmosphere from the leak portion, so that the original diffusion prevention effect cannot be fully realized.
For an apparatus for diagnosing the presence of faults (fuel vapor leaks) in the fuel vapor treatment unit, the following methods have been contemplated.
That is to say, fault diagnosis of a fuel vapor treatment unit is carried out by closing a purge control valve disposed in a purge passage between a canister and an intake passage at the time of diagnosis, being after the engine has stopped or while the vehicle is travelling, then supplying air which is pressurized by a pump device provided for diagnosis, to inside a sealed fuel vapor supply system on the downstream side of the purge control valve, and making a judgement of a pressure rise of the fuel vapor supply system, or a time until a predetermined pressure is reached.
After the engine has stopped however, the quantity of vapor generated inside the fuel tank due to the heat from the engine is comparatively large, and hence this is an unsuitable condition for accurate fault diagnosis. Moreover, when the vehicle is travelling, in addition to the engine heat, there is the likelihood during fault diagnosis of influences due to changes in atmospheric pressure from travelling along roads of different altitudes. Furthermore, the liquid level inside the fuel tank also is agitated due to vibrations from the engine or the road surface, thus becoming a source of erroneous diagnosis.
The present invention takes into consideration such heretofore problems, with the object of being able to prevent erroneous diagnosis in a fuel vapor treatment unit, and thus carry out accurate diagnosis.
Furthermore, without requiring modification of the hardware for fault diagnosis itself, it is an object to improve diagnosis accuracy without increasing cost, by making the timing for executing fault diagnosis a suitable timing.
Moreover, it is an object to speed up execution of fault diagnosis and thus avoid beforehand, adverse affects on handling due to faults.
SUMMARY OF THE INVENTION
Therefore, with the present invention, with a fuel vapor treatment unit which temporarily adsorbs fuel vapor from a fuel tank of an internal combustion engine into an adsorption unit via a vapor passage, and then processes the fuel vapor by drawing this into an engine intake system from the adsorption unit under predetermined engine operating conditions, via a purge passage in which is disposed a purge control valve, the presence of a fault is diagnosed in the following manner.
A condition for close to engine start time is detected for example based on an ignition switch signal, or an engine rotation signal, and fault diagnosis of the fuel vapor treatment unit is permitted on the proviso that this condition is detected.
When the fault diagnosis is permitted, the purge control valve is closed, and air which is pressurized by a pump device, is supplied to inside the sealed fuel vapor treatment unit.
Then, when there is a fuel vapor leak (fault) in the fuel vapor treatment unit, the pressure inside the fuel vapor treatment unit is lowered in comparison with the pressure when there are no leaks. Therefore, by detecting the pressure condition, the presence of a fault can be diagnosed.
In this way, since fault diagnosis of the fuel vapor treatment unit is performed under the proviso that the engine condition is close to start time, the influence of heat from the engine after the engine has stopped, and the influence of vibration due to the road surface when the vehicle is travelling and of atmospheric pressure changes due to differences in altitude can be simultaneously avoided, so that erroneous diagnosis due to these influences can be prevented, and fault diagnosis accuracy thus improved.
Furthermore, by appropriately controlling the timing for executing fault diagnosis without requiring special modifications of the hardware for fault diagnosis, diagnosis accuracy can be improved without increasing cost.
Moreover, since diagnosis is executed when the engine condition is close to start time, adverse affects on handling due to faults can be avoided beforehand.
Furthermore, the construction may be such that a temperature condition inside the fuel vapor treatment unit is detected, and fault diagnosis of the fuel vapor treatment unit is permitted on the proviso that the interior of the fuel vapor treatment unit is detected to be a low temperature condition equal to or below a predetermined temperature.
That is to say, fault diagnosis of the fuel vapor treatment unit is permitted on the proviso that, in addition to the engine condition being close to start time, the interior of the fuel vapor treatment unit is a lower temperature condition equal to or below a predetermined temperature.
In this way, the influence of heat from the engine in the case such as at the time of high temperature restarting (hot restart time) can be avoided, and hence fault diagnosis accuracy can be further improved.
Furthermore, the construction may be such that for the temperature condition inside the fuel vapor treatment unit, at least one of fuel temperature, engine cooling water temperature, atmospheric temperature, and the temperature of the adsorbent inside the adsorption unit is detected.
In this way, by detecting for example the fuel temperature or the temperature of the adsorbent inside the adsorption unit, the temperature conditions inside the fuel vapor treatment unit can be detected in a high accuracy. Moreover, in the case where the detection value of the engine cooling water temperature, or the atmospheric temperature is used, a sensor such as the water temperature sensor or the intake air temperature sensor to be used for other control, can be appropriated, so that temperature conditions can be detected without increasing costs.
Moreover, fault diagnosis of the fuel vapor treatment unit may be permitted also on the proviso that a fuel quantity inside the fuel tank is within a predetermined range.
In this way, the volume of the air space inside the fuel vapor treatment unit at the time of fault diagnosis is limited. Therefore diagnosis time can be shortened, and erroneous judgment thus prevented.
Moreover, a time after starting power supply to a control circuit of the engine but before starting the engine, may be detected as a condition for close to engine start time.
That is to say, pre-start time after switching on the ignition switch to start power supply to the engine control circuit, and before switching on the starting switch, is detected as a condition for close to engine start time.
In this way, heating and agitation of the fuel inside the fuel tank, due to engine operation, can be prevented, so that fault diagnosis accuracy can be further improved.
Furthermore, in the case of performing diagnosis before starting the engine, fault diagnosis of the fuel vapor treatment unit may be permitted also on the proviso that there is no refueling.
In this way, erroneous judgment due to pressure changes foll

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