ELECTRIC COOLING FAN
The radiator cooling fan is driven by a variable speed 500W electric motor. An electronic cooling fan module, located on the cooling fan motor and shroud assembly, drives the fan motor. The cooling fan module control circuit is supplied by a ignition switched, 20 amp fused power supply from powertrain relay No. 1. The battery power for the cooling fan motor is supplied by the 80 amp fuse adjacent to the front power distribution box.
When the ignition is switched to ON position II, the cooling fan module receives a Pulse Width Modulation (PWM) control signal proportional to the engine cooling requirements from the Powertrain Control Module (PCM). In response to the PCM control signal, the cooling fan module switches the fan motor on and off and varies fan speed between 300 RPM to 2900 RPM using PWM drive voltage.
After the ignition is switched off, the PCM is deactivated. However, the need for cooling fan operation can still exist. As the engine is switched off, the A/C Control Module (ACCM) notes the cylinder head temperature Standard Corporate Protocol (SCP) message and provides a control signal to the cooling fan control module for a fixed period, operating the cooling fan motor. The engine off fan operational time period is determined by the ACCM based on the SCP temperature message. The PCM calculates the engine cooling requirement from signal inputs received from the Cylinder Head Temperature (CHT) sensor, A/C pressure switch, A/C compressor status and transmission fluid temperature.
The A/C pressure switch, located in the A/C high pressure line, is a pressure transducer sensing refrigerant system high side pressure. The feedback voltage from the transducer supplies the PCM with a signal proportional to refrigerant pressure. The PCM uses the refrigerant pressure signal for coolant fan requirement and compressor clutch control.
FAIL SAFE COOLING
The 3.0L V6 PCM is programmed with a function that monitors engine temperature and performs actions that prolong safe engine operation by controlling engine temperature. This Fail Safe Cooling (FSC) strategy is fully controlled by the PCM. The FSC strategy on V6 engine is made possible by monitoring the engine temperature with a Cylinder Head Temperature (CHT) sensor (metal contact) instead of a Engine Coolant Temperature (ECT) sensor.
If the PCM detects that the engine temperature is excessively high, it switches off the fuel injector(s) of one or more cylinders. With no fuel being injected, ambient air is pumped through the cylinder cooling the engine. By switching individual injectors off for a period of time and in a sequence determined by the PCM, engine temperature can be controlled to allow the vehicle to be driven for a short distance.
The overall engine cooling strategy can be divided into 5 stages. The FSC strategy operates in the 3 top stages.
Sunday, November 8th, 2009 AT 8:18 AM