Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
1998-07-13
2001-07-17
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
C073S116070, C073S117020
Reexamination Certificate
active
06260411
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for suppressing the influence of an empty fuel tank on the on-board-diagnosis for a motor vehicle driven by an internal combustion engine.
BACKGROUND OF THE INVENTION
Statutory regulations require that all exhaust-gas relevant components of a motor vehicle be diagnosed. Faults which lead to the exhaust-gas limit value to be exceeded by a factor of 1.5 must be detected in running operation of the vehicle and, for example, indicated by switching on a fault lamp. When the diagnostic lamp illuminates, the driver is instructed to immediately go to a service facility and have the fault corrected. An unnecessary visit to the service facility as a consequence of an erroneously illuminated fault lamp is to be avoided.
The statutes permit diagnostic functions to be switched off or permit a delayed entry of a fault when the environmental conditions make an erroneous fault detection probable, for example, when the air pressure is too low at high elevations.
U.S. Pat. No. 5,158,059 discloses a method in this context wherein the detection or registration of faults is suppressed when the tank is empty. This measure is supported by the possibility that, for an almost empty tank, fuel as well as air reaches the fuel supply of the engine. As a consequence, the precision of the fuel metering deteriorates. Considerable mixture leaning takes place which, in turn, can lead to a significant enrichment reaction in a closed air/fuel ratio control loop. The mixture deviations, especially the leaning of the fuel mixture, can cause combustion misfires. Depending upon the construction of the fuel tank, several kilometers can still be travelled from the first occurrence of the leaning of the fuel mixture until the vehicle comes to final standstill. This effect affects a series of diagnostic functions which react with fault announcements. These fault announcements do not result from a defective component. For this reason, the fault announcements should not lead to driving the fault lamp. The diagnostic functions which are affected are, for example, the detection of combustion misfires, the diagnosis of the fuel supply system, the diagnosis of the &lgr;-control by means of a &lgr;-probe rearward of the catalytic converter, the diagnosis of the catalytic converter and the diagnosis of the &lgr;-probe.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a method for evaluating fault announcements of on-board diagnostic functions in combination with the fill level of the fuel tank so that fault announcements, which result because of a deficiency of fuel, are not registered while, on the other hand, ensuring that proper faults, which do not result from a deficiency of fuel, are detected even when the fuel tank level is low.
The method of the invention is for diagnosing an internal combustion engine wherein a fault is detected and registered under specific conditions. The engine is supplied with fuel from a fuel tank and the method includes the steps of: determining the fill level of fuel in the fuel tank; and, when the fill level is below a lower threshold value, registering a fault only when a delay time span has elapsed since a first-time occurrence in an operating phase of the engine and when the fault still continues to occur.
The invention is based on the fact that a fault announcement, which is caused by a defect, occurs over a longer time interval than does an error caused by a deficiency of fuel. Only a limited quantity of fuel can be inducted from the first occurrence of the effects of a tank driven to empty until the engine finally comes to standstill because of a lack of fuel. The distance travelled by a motor vehicle with an empty tank is, as a rule, shorter than the distance which corresponds to the exhaust-gas test Federal Test Procedure 75 (FTP75). An essential feature of the invention is that the fault announcement is delayed for that time span in which the vehicle can be driven with an almost empty tank without retanking.
Advantageously, the delay time span is coupled to the consumption of a specific minimum quantity of fuel. A measure for this quantity can be formed from the data available in the control apparatus, such as the load signal or the injection times. Alternatively, a fixed delay time can be pregiven. The delay time can also be variable in dependence upon operating parameters such as by decrementing a pregiven value. The counter count increment increases with increasing load and/or rpm. If faults still occur after this time span, then they are not caused by a temporary deficiency of fuel; instead, they are caused by a defect and will then be registered as faults.
In the above way, an unwanted driving of the fault lamp when there is a deficiency of fuel because of an empty tank is advantageously prevented.
It is also advantageous that a proper fault is indicated in any event. Even when an empty tank is indicated continuously because of a defective level indicator or the driver drives almost exclusively with only a very low level of fuel, driving the fault lamp is not prevented for a valid fault. It has been shown that, when carrying out the method of the invention, a vehicle in the exhaust-gas test at the authority responsible for such tests does not perform significantly differently than without this fault suppression for an empty tank.
It is likewise advantageous to detect retanking and to consider the retanking because retanking changes the preconditions for the fault registration.
According to the method of the invention, only a delay occurs of the entering of a fault when a defective fuel tank level transducer is present which erroneously indicates an empty tank. However, it is ensured that after a renewed conditioning of the vehicle for a FTP75 test and the execution of this test, a proper fault is detected.
REFERENCES:
patent: 5158059 (1992-10-01), Kuroda
patent: 5275144 (1994-01-01), Gross
patent: 5723780 (1998-03-01), Miwa et al.
Esteghlal Gholamabas
Mallebrein Georg
Sorg Wilhelm
Davis Octavia
Fuller Benjamin R.
Ottesen Walter
Robert & Bosch GmbH
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