The drive motor generator power inverter module (PIM) assembly converts high voltage direct current (DC) electrical energy to 3 phase alternating current (AC) electrical energy. The accessory DC power converter module (APM) converts high voltage DC electric energy into low voltage (14 V) and intermediate voltage (42 V) in order to charge the vehicles accessory battery and supply electric energy to the 42 V power steering system. The APM and PIM are fastened together and are referred to as the drive motor/generator control module assembly. The engine control module (ECM) monitors a temperature sensor in the power electronics cooling system and operates the radiator fan and the power electronics coolant pump in response to power electronics cooling system temperature.

The pump system will always be activated when the vehicle is on and propulsion is available. The pump system will also be activated when the vehicle is on and propulsion is not available if the algorithms determine that cooling is needed. The HCP and ECM determine the speed/flow and control the power electronics coolant pump system. This circuit is a single driver control to a relay and both pumps are in parallel powered by a fuse in the auxiliary BEC. The power electronics coolant pump control shall be on during a key crank, after a successful key crank, during a jump assist event or after a key off when the power electronics coolant is extremely hot.

Cooling Cycle

Coolant flows from the radiator outlet through the PIM and back toward the radiator. From the PIM, the coolant flows through the air separator and through two coolant pumps before entering the radiator. Coolant also flows to and from the surge tank as the system requires.

Efficient operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components:

Coolant

The drive motor/generator control module assembly is cooled by a solution made up of a 50-50 mixture of DEX-COOL® and De-Ionized water. De-Ionized water is required to prevent corrosion from effecting heatsink performance. The coolant solution carries excess heat away from the drive motor/generator control module assembly to the radiator, where the heat is dissipated to the atmosphere. Always use pre-mixed coolant and never use tap water in the power electronics coolant system.

Radiator

The radiator is a heat exchanger. It consists of a core and two end tanks. The aluminum core is a tube and fin crossflow design that extends from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer to the atmosphere.

The inlet and outlet end tanks are a molded, high temperature, nylon reinforced plastic material. A high temperature rubber gasket seals the end tank flange edge to the aluminum core. The end tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core.

The radiator removes heat from the coolant passing through it. The fins on the core transfer heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

Pressure Cap

The pressure cap seals the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring that protects the radiator by relieving pressure that exceeds 5 psi. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator and/or coolant hoses to collapse.

The pressure cap allows cooling system pressure to build up as the temperature increases. As the pressure builds, the boiling point of the coolant increases. The hotter the coolant is, the faster the heat transfers from the radiator to the cooler, passing air.

The pressure in the cooling system can get too high. When the cooling system pressure exceeds the rating of the pressure cap, it raises the pressure valve, venting the excess pressure.

As the PIM cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the surge tank. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator and coolant hoses from collapsing.

Surge Tank

The surge tank is a plastic tank that the pressure cap mounts onto. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill point and a central air bleed location. During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.

Air Separator

The air separator is a plastic tank that aids in the removal of air from the cooling system. The air separator is located in the cavity behind the left hand headlamp. Coolant enters the air separator from an upper hose that attaches to the PIM. Coolant exits the air separator from a lower hose that attaches to the coolant pumps. A third hose, attached to the top of the air separator, allows air to escape the cooling system through the surge tank.

Coolant Pumps

There are two coolant pumps, connected in series that are located on the upper right hand area of the fan shroud. These pumps control the flow of coolant through the hybrid cooling system.