vehicle is in heavy traffic and then moves (i.e., vehicle speed increases above zero or a low threshold) or the operator presses on the accelerator to increase engine speed. In the case of a temporary override, the system will return to monitoring the idle shutdown prerequisites 10. An override may also be instituted by the operator manuallyentering an override command 18,forexample, by a key press entry.In this case,the system will wait for a reset. 

10 15 20 25 [0028] Absent an override, idle shutdown procedure control passes to temperature monitoring 20. The ISD continually monitors the engine coolant temperature 20 and comparesthe temperature tofirstandsecondthresh- old temperatures. The threshold temperatures define three temperature zones, Zone 1 at or below the first threshold temperature, Zone 2 above the first threshold temperature and at or below the second threshold tem- perature, and Zone 3 above the second threshold tem- perature.The zones identify temperature rangesrelating to the risk of damage to the engine if shutdown in that zone. Zone 1 represents a temperature range in which shutdown is not likely result in engine damage, that is, the normal shutdown range. Zone 2 represents a tem- perature range where a shutdown has a moderate risk of engine damage and some cooling is required prior to shutdown.Zone 3 representsa temperature range where there is a high risk of engine damage on if shutdown occurs and more vigorous cooling measures are re- quired. 

[0029] The actual threshold temperatures will be de- termined using factors for the specific engine, duty cycle of the vehicle, and the ability to dissipate heat in the op- erating environment. For example, on a 16 liter engine in an over-the-highway truck, which runs for much of its duty cycle at steady state high revolutions, a first thresh- old temperature may be 187°F. (approximately 86 °C), which isapproximately theopen thermostattemperature. Continuing the example, the second threshold tempera- ture may be 200° F. (approximately 93 °C), above which approaches the boiling point of water. For vocational trucks and trucks with power takeoff equipment, which operate cyclically, the threshold temperatures may be different. Those skilled in the art will appreciate how to setthe thresholdstoprotectanenginefromheatdamage. For operating environments of extremely high ambient temperatures, the threshold temperatures may be ad- justed downward by the ISD to compensate for the di- minished ability of the engine to cool. 

[0030] Each of the zones is associated with specific measuresthe ISD willtake if the engine-associated tem- perature is found to be in that zone. If the engine-asso- ciated temperature is below the first threshold tempera- ture, which is the generally safe shutdown zone, the en- gine cooling fan isturned offorremains off22.Ifanover- ride is then found to be active 24, the ISD reverts to Step 14 and the countdown is suspended. If the override is notactive,the idlecountdown continues,untilexpiration, at which time the engine is shutdown 26. 

[0031] If the ISD detects the engine-associated tem- perature above the first threshold temperature but at or below thesecond threshold temperature, thatis,in Zone 2,the engine cooling fan isturnedon 28tocoolthe engine to below the first threshold temperature. Temperature monitoring 20 continues, and once the engine-associat- ed temperature is determined to be in Zone 1, the ISD institutes Step 22, and the engine cooling fan is turned off. If the override is not active, the idle count down con- tinues to expiration 26, and the engine is shutdown. 

[0032] If the engine-associated temperature is above the second threshold temperature, that is, the tempera- ture is determined to be in Zone 3, the cooling fan is activated and the engine speed is raised above idle 30 to increase the cooling fan speed for more rapid cooling of the engine. The controller monitors the engine-asso- ciated temperature 20 to ensure that the engine temper- ature is decreasing and will adjust the engine speed ac- cordingly.Oncethe coolanttemperature drops below the secondthreshold temperature,thatis,decreasestoZone 2, the ISD method institutes Step 28, engine speed is returned to normal idle speed, and the fan operates at a speed reduced from that of the Zone 3 controlled speed. The methodcontinues fromStep 28 as describedabove. 

[0033] As described, Step 30 is appropriate for a cool- ing fan that is directly driven by the engine, where fan speed is related to engine speed, as recited in the an- nexed independent claims. 

[0034] In addition, the vehicle may be equipped with a variable speed coolant pump, which may be operated similar to the fan to increase engine cooling when need- ed. Controlling the coolant pump may be used when the engine-associated temperature is in Zone 3. In addition to increasing the fan speed, the coolant pump flow rate may be increased to increase the cooling effect on the engine until the temperature is in Zone 2. 

[0035] The engine-associated temperature may be de- termined from the engine coolant temperature, the en- gine oil temperature, transmission fluid temperature, and/or other parameters measured by the VECU or en- gine management system (EMS). One or a combination of these temperature measurements can be used by the ISD to determine which temperature zone the engine is in, that is, whether it is safe for the engine and its related components to be shut down by the ISD. 

[0036] As mentioned, the ISD function can be control- led by a vehicle electronic control unit (VECU), which typically monitors and controls the vehicle’s various sys- tems. Alternatively, the ISD can be located within the engine management system (EMS). The ISD function operates the engine cooling fan, control engine speed, as well as control other related systems that have an effect on the operating temperature. 

[0037] The ISD includes a threshold limit incorporated into the cooling fan engagement instruction. For exam- ple,when the engine-associatedtemperature falls tojust slightlyabove the thermostatopening temperature orfirst threshold temperature, the cooling fan disengages. 

