The Prius That Shook.. - VFAQ Prius Site

Many departments were complaining that the inverter
would stop immediately after it was put to tests inside the
hot tunnel. Since it was in winter, the car had no problem
running outside. In the hot environment, the IGBT itself
became hot, and the sensor to protect the IGBT from
overheating kicked in and stopped the car. This was
Yasuho's first concern when he started designing the IGBT.
The cause seemed to be the heat sink. Its heat
conductivity was half what it should be and the loss was 20%
more than the estimate. In addition, Yasuho did not have
enough time to tune it. This time, his group had to work
on heat and loss. It was another case of double torture.
At the start, copper was used for the heat sink because of
its high heat conductivity. Since copper has low heat
resistance, it cools quite effectively but it also deteriorates
quickly. Yasuho estimated, based on his past research and
experience, that copper would deteriorate and fail to
deliver the initial performance level in just two to three
years. After receiving approval from Uchiyamada to make a
change, he had used a new material for the heat sink. This
material could maintain cooling capability but had low
initial cooling capacity. It would not cool quickly so that
the IGBT continually became hot.
"The copper won't last, and there are no alternatives.
There is no time, either."
After thinking through the problem, Yasuho revisited
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