Internal-combustion engines – Cooling – Indicators and safety devices
Reexamination Certificate
2000-03-15
2001-10-16
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Cooling
Indicators and safety devices
C073S198000
Reexamination Certificate
active
06302065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to systems for estimating engine coolant temperature in a vehicle equipped with an internal combustion engine, and more particularly, to using this information to determine whether the performance of the cooling system is degraded.
BACKGROUND OF THE INVENTION
Vehicle cooling systems typically have a coolant temperature sensor for providing coolant temperature information to the electronic engine controller and a thermostat for providing constant coolant temperature control. Coolant temperature is a very important parameter in several engine control strategies, and in particular in an electronically controlled fuel supply system. If the coolant temperature sensor is degraded, fuel consumption and emission strategy may be degraded. For example, if the coolant temperature sensor is indicating that the engine is cold, rather than warmed up, a rich fuel-air mixture may be supplied longer than necessary, thus potentially degrading emissions and fuel efficiency.
One method of diagnosing the engine coolant temperature sensor is described in U.S. Pat. No. 4,274,381. Engine coolant temperature is inferred from another temperature sensor such as the temperature sensor of the catalytic converter. This inferred value is compared to the value read by the coolant temperature sensor. If the two values are not the same, degradation is indicated. Then, a signal corresponding to the output of the engine coolant temperature sensor under normal engine operating conditions replaces the output of the degraded coolant temperature sensor.
The inventor herein has recognized a disadvantage with this approach. In particular, there is not a way to determine which one of the above mentioned sensors is degraded. Also, providing a predetermined signal to replace the degraded sensor information is not an accurate representation of the actual operating conditions, especially at high/low ambient temperatures, or at engine start-up.
Another disadvantage is that this method does not diagnose the cooling system thermostat. If the thermostat performance is degraded, efficient temperature levels will not be maintained under all operating conditions, and thus, vehicle performance, fuel efficiency and emission control may be degraded. Further, the prior art does not take into account the state of the thermostat (open or closed) when estimating coolant temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for diagnosing a cooling system in an internal combustion engine, and in particular to diagnosing the engine coolant temperature sensor and the thermostat.
The above object is achieved and disadvantages of prior approaches overcome by a method for diagnosing a cooling system having an engine coolant temperature sensor and a thermostat in an internal combustion engine, the method comprising: estimating an engine coolant temperature based on an operating condition and a characteristic of the thermostat; reading the engine coolant temperature sensor; comparing said estimate with said reading; and determining operability of the system based on said comparison.
An advantage of the above object of the invention is that a more precise method of diagnosing the engine coolant temperature sensor is developed. By taking into account a characteristic of the thermostat, it is possible to more accurately estimate coolant temperature since the cooling system performs differently depending on the operation of the thermostat. The electronic engine controller can use a more accurate estimate of the coolant temperature in case the coolant temperature sensor performance is degraded.
In another aspect of the present invention, a method for estimating an engine coolant temperature and diagnosing a coolant temperature sensor and a thermostat is developed. This method comprises determining a first estimate of heat added to the coolant based on an engine operating condition; determining a second estimate of coolant temperature based on said first estimate; reading the coolant temperature sensor; comparing said estimate with said reading; determining whether the coolant temperature sensor is functioning properly based on said comparing; and determining whether the thermostat is functioning properly based on said comparing. By using heat added to estimate coolant temperature, an accurate model is obtained to improve estimation. This ability contributes to improved vehicle performance, fuel efficiency and emissions control.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Ford Global Technologies Inc.
Harris Katrina B.
Voutyras Julia
Wolfe Willis R.
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