Cooling System: Description and Operation

Description

Various semiconductor devices are utilized within the HPCU (the core component for controlling the hybrid vehicle), and these devices generate unavoidable heat when in operation. These devices are directly linked to high voltage, so their heat level is higher than the electrical devices found in a conventional combustion engine vehicle. Overheating lowers the efficiency of the control devices and limits proper operation control. In addition, the semiconductor can melt in extreme high temperatures (the devices are always turned ON) and such overheating causes failure.
Therefore, it is very important to properly cool the HPCU related components. For this purpose, Hybrid vehicle has a supplementary water cooling line in addition to the existing engine cooling line. The reason the system does not share the engine cooling line is the difference in the temperatures of the two systems. For example, the engine coolant sets the overheat temperature as 100°C,but the HPCU limits the normal operating temperature at 75°C
When examining the effects of temperature on the inverter more closely, the inverter outputs about 80% of rated output at 75°C, and its output starts to be significantly limited at 90°C. When the temperature reaches 95°C, the inverter output is shut down.
LDC is even more sensitive to high temperature. It outputs 100% of the rated output up to 65°C, but it becomes limited to about 60% at 75°C, then down to 25% at 80°C. The LDC output shuts down completely at 85°C.
For more detailed information, refer to the DTC Service Data section in later in this manual.
An electric water pump is newly added to circulate the coolant. It is directly operated by the MCU. As shown in the diagram, the additional cooling line also cools the HSG. Because it is independent from the engine cooling line, a separate coolant reservoir tank is needed and the tank is mounted near the HPCU.