Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2000-02-22
2001-08-07
Moullis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
Reexamination Certificate
active
06269803
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a vehicle fuel system having on-board diagnostics for testing the system for vapor integrity.
BACKGROUND OF THE INVENTION
Vehicle fuel systems are required to control emission of fuel vapor. This is done by collecting vapor emitted from the fuel tank in a purge canister containing carbon to absorb the vapor. The canister is purged of collected vapor when the engine is running by drawing air through the canister into the engine, relying on manifold vacuum. The system is sealed except for venting to the atmosphere via the purge canister. On-board testing is required to ensure that escape of vapor from the sealed system does not exceed prescribed limits. Typical known vapor integrity testing systems are described U.S. Pat. Nos. 5,333,590 and 5,765,121.
The latter patent describes a basic test in which the manifold vacuum is used to pump out the fuel tank and the return of tank pressure to atmospheric (“bleedup”) is monitored. If bleedup exceeds a certain threshold value R the system is determined to have an unacceptable vapor integrity. If the bleedup is less than R, it assumed that vapor integrity is acceptable. Vapor loss below a certain level cannot be reliably detected with this basic system because vapor generation from fuel in the tank can cause pressure in the evacuated system to recover more rapidly than ingress of air due where loss of vapor integrity is small.
Vapor generation depends on many factor, including ambient temperature and vapor volume, that is the volume of free space above the fuel tank and in the purge canister and connecting passages. Vapor volume is itself directly related to fuel level.
Thus, in order to improve the sensitivity of the basic bleedup test, measures must be taken to correct for different operating conditions, particularly the fuel level and the rate of vapor generation in the tank.
For example, U.S. Pat. No. 5,333,590 uses a threshold value R which is not fixed but is related to vapor volume and fuel temperature.
It is also known to improve the sensitivity of vapor integrity testing by using a two stage test. The first stage is a bleedup test in which pressure increase over a certain period (period_A) is measured. A second stage is carried out in which pressure rise of the closed system from atmospheric over a second period (period_B) is monitored. The second stage gives an indication of vapor generation in the tank under prevailing conditions. A constant scaling factor is used to deduct a proportion of pressure rise found during the second stage to provide a value which more closely represents the level of bleedup due to ingress of air into the tank during the first stage of the test.
SUMMARY OF THE INVENTION
According to the present invention a vehicle fuel system with on-board diagnostics for vapor integrity testing comprises a vehicle fuel system with on-board diagnostics for vapor integrity testing comprising: a) a fuel tank for containing fuel for delivery to an internal combustion engine; b) a purge canister connected to the space in the tank above the fuel; c) a canister vent valve (CVV) for connecting the purge canister to the atmosphere; d) a purge valve for connecting the purge canister to the engine; and e) an electronic control unit (ECU) arranged for monitoring pressure and fuel level in the tank and other engine, vehicle and ambient conditions and for controlling opening and closing of the valves; f) the CVV and the purge valve being controlled by the ECU for venting the tank to atmosphere via the purge canister (purge valve closed, CVV open), and for purging vapor from the canister by allowing air to be drawn through the canister by manifold vacuum (both valves open); g) the ECU being arranged to carry out a periodic vapor integrity test, when the engine is running, the vapor integrity test including (i) reducing the pressure in the tank, closing the system and allowing pressure in the system to recover towards atmospheric (bleedup), (ii) making a series of pressure measurements at intervals during bleedup to give a series of timed pressure values and (ii) calculation of vapor rate from values representing pressure gradient and the rate of change of pressure gradient derived from the pressure values.
The improved fuel system test contemplated by the invention is preferably implemented using the vehicle's existing electronic engine control unit and the fuel system pressure sensor which is used for other purposes. As a consequence, the benefits of the invention may be obtained at very little additional cost.
These and other features and advantages of the present invention may be better understood by considering the following detailed description of a preferred embodiment of the invention.
During the course of this description, frequent reference will be made to the attached drawings.
REFERENCES:
patent: 5460143 (1995-10-01), Narita
patent: 5463998 (1995-11-01), Denz et al.
patent: 5575265 (1996-11-01), Kurihara et al.
patent: 5765540 (1998-06-01), Ishii et al.
patent: 6016792 (2000-01-01), Kawano et al.
patent: 6105556 (2000-08-01), Takaku et al.
Drouillard Jerome R.
Jaguar Cars Limited
Moullis Thomas N.
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