Model-based diagnostic method for an engine cooling system

Internal-combustion engines – Cooling – Indicators and safety devices

Reexamination Certificate

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Details

C123S1980DA

Reexamination Certificate

active

06321695

ABSTRACT:

TECHNICAL FIELD
This invention is directed to a method for detecting improper operation of an engine cooling system through the use of an engine coolant temperature model.
BACKGROUND OF THE INVENTION
A significant aspect of state-of-the-art automotive engine control pertains to so-called on-board-diagnosis of various engine components or sensors, particularly when improper operation of such components or sensors can adversely influence the engine emission controls. In the case of an engine cooling system, the diagnosis involves determining if the engine thermostat is operating correctly, and if the engine coolant temperature sensor is providing an accurate measurement. If the diagnosis reveals faulty operation of the thermostat or engine coolant sensor, the engine controller stores the fault information and activates a “check engine” indicator to advise the driver that the vehicle should be serviced soon.
While any component or sensor could theoretically be diagnosed through the use of additional sensors, such additional sensors significantly increase the cost of implementing the diagnostic function, and raise concerns over the reliability of the additional sensors themselves. Accordingly, there is a strong desire to implement the diagnostic functions using existing sensor information only. Further, it must be recognized that engine operation varies widely depending on both the driver and the environment. In the case of the engine cooling system, for example, the thermostat operation and the measured coolant temperature are influenced by a number of factors, such as engine fueling, driving schedule, heater operation, ambient air temperature, engine speed, vehicle speed, etc. Diagnosing methods that take many of these factors into account can be very complex and are typically very difficult to calibrate properly.
Accordingly, what is needed is a method of reliably diagnosing the proper operation of an engine cooling system that does not involve the use of additional sensors and that is easy to calibrate.
SUMMARY OF THE INVENTION
The present invention is directed to an improved method of diagnosing an engine cooling system through the use of a coolant temperature model based on existing sensor information. Proper operation of the engine thermostat and coolant temperature sensor is diagnosed based on an initial comparison of coolant temperature to ambient air temperature at key-on and a later comparison of coolant temperature to a predetermined regulated temperature. According to the invention, the coolant temperature model is used to trigger the initiation of the later comparison to ensure that the diagnostic is performed when the engine is fully warmed up. Advantageously, the modeled coolant temperature may be used for control purposes in the event that the diagnostic detects faulty operation of the coolant temperature sensor.


REFERENCES:
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patent: 5153835 (1992-10-01), Hashimoto et al.
patent: 5884243 (1999-03-01), Taniguchi et al.
patent: 6128948 (2000-10-01), Shi et al.

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