| 摘要 |
Electronic processing means are utilized in a composite measurement of performance of an engine cooling system thermostat, with diagnostic procedures to ensure viable measurement. The speed of the engine is initially tested to ensure the engine is at high idle speed, so that temperature in the cooling system will increase to that at which the thermostat will normally operate; and during the testing, the speed is continuously monitored to be sure it remains close to the initial test speed (near high idle) to minimize coolant pump pressure variations due to engine speed. Three temperature diagnostics are performed to ensure a viable test: first, if the temperature ever exceeds 15 DEG over the rated thermostat temperature, the test is terminated in a fault since the thermostat is presumed to be stuck in the closed position; second, if the temperature fails to increase by at least 2 DEG for each 2 minutes of operation above rated speed, the test is terminated in a fault since it is assumed that the thermostat is stuck in the open position; third, if the test is not completed within 5 minutes after the temperature reaching 5 DEG less than the rated thermostat temperature, the test is terminated in a fault since the thermostat operation is too imprecise to reliably perform the measurements of the operation (such as laggardly or stuck partially open). The actual thermostat operation measurements are the highest temperature reached before sensing either a temperature drop of 2 DEG below the highest temperature sensed theretofore, or sensing a pressure drop of 5 psi below the highest pressure sensed theretofore.
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