Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
2002-04-08
2004-05-04
Nguyen, Thu V. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
Reexamination Certificate
active
06732025
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to on board diagnostic systems for motor vehicles, and more particularly to a method for determining whether a thermostat in a motor vehicle is operating properly.
BACKGROUND OF THE INVENTION
An on board diagnostic system is an emissions diagnostic system whose purpose is to monitor all systems and components in a vehicle that can affect emissions and to inform the driver of that vehicle when an emissions-related problem has occurred. An emissions-related problem is detected when either a system or a deterioration of a system (or component thereof) causes vehicle emissions to exceed certain pre-selected thresholds. On board diagnostics are currently employed in passenger cars, light-duty trucks, and medium-duty vehicles in all 50 states and Canada and are quickly becoming used worldwide.
Generally, on board diagnostics check current operating conditions against enable conditions to determine if any monitoring program should run. If enabled, the monitoring program performs calculations based on certain sensor information and other related variables. The resulting diagnostic parameters are then checked against calibrated threshold values. These threshold values are typically correlated to emissions performance through standardized test procedures. If the resulting diagnostic parameters are less than the calibrated threshold values, then a pass status is processed. If the resulting diagnostic parameters are greater than the thresholds, then a fail status may be processed. The on board diagnostics system typically processes a failure by illuminating the “Check Engine” malfunction indicator lamp on the instrument panel and stores a fault code in the powertrain controller for later retrieval by a service technician.
Although many vehicle system components are monitored by way of conventional on board diagnostic systems, there is no diagnostic which monitors whether the thermostat of a motor vehicle is operating properly. Accordingly, it would be desirable to provide an on board diagnostic for determining whether a thermostat in a motor vehicle is operating properly.
SUMMARY OF THE INVENTION
The above and other objects are provided by a method which includes an engine warm-up model and a thermostat diagnostic. The engine warm-up model predicts an engine coolant temperature at a given time after start-up. This is based on the engine coolant temperature at start-up, ambient air temperature, and how the vehicle is driven subsequent to start-up. This predicted engine coolant temperature is compared to the actual engine coolant temperature as read by an engine coolant temperature sensor. The error between the predicted engine coolant temperature and the actual engine coolant temperature is calculated and integrated over time. The thermostat diagnostic runs at a pre-selected time after start-up when the engine coolant temperature is above a threshold temperature and compares the integrated error to a predetermined threshold value. Depending upon the results of the comparison, a pass, fail, or inconclusive condition is determined.
The predetermined threshold value is calculated to discern between a properly operating thermostat operating in a vehicle which is experiencing the maximum heat loss/minimum heat gain possible and an improperly operating thermostat operating in a vehicle which is experiencing the minimum heat loss/maximum heat gain possible. The properly operating thermostat/maximum heat loss/minimum heat gain scenario provides the slowest possible engine coolant temperature warm-up for a vehicle with a properly operating thermostat. Conversely, the improperly operating thermostat/minimum heat loss/maximum heat gain scenario provides the fastest possible engine coolant temperature warm-up for a vehicle with an improperly operating thermostat.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 6200021 (2001-03-01), Mitsutani et al.
patent: 6240774 (2001-06-01), Niki et al.
patent: 6302065 (2001-10-01), Davison
Aldridge Susan A.
Dawson Gary D.
Pallach Gary M
Ploucha David P.
Reese, II Ronald A
Bacon, Jr. Edwin W.
DaimlerChrysler Corporation
Nguyen Thu V.
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