Drive device

1. A drive unit, comprising:

an electric motor;

a drive unit casing accommodating therein the electric motor;

an inverter that controls the electric motor; and

a flow passage in which a refrigerant passes therein in order to cool the inverter, wherein

the inverter is mounted on the drive unit casing such that a heat sink, united with a substrate of the inverter, defines a space that is in communication with the flow passage on a portion thereof opposed to the drive unit casing,

the space is compartmented by a separator into a first chamber facing the heat sink and a second chamber facing the drive unit casing, and

the heat sink comprises heat-sink side fins extending into the first chamber and apart from the separator.

2. The drive unit according to claim 1 , wherein the drive unit casing comprises drive-unit-side fins extending into the second chamber.

3. The drive unit according to claim 2 , wherein the drive-unit-side fins are apart from the separator.

4. The drive unit according to claim 3 , wherein the separator comprises a low thermal conductive member made of a material of low thermal conductivity.

5. The drive unit according to claim 3 , wherein the separator comprises a separation member and a low thermal conductive member provided along the separation member and made of a material of low thermal conductivity.

6. The drive unit according to claim 3 , wherein the separator comprises separation members with a low thermal conductive portion therebetween.

7. The drive unit according to claim 2 , wherein the separator comprises a low thermal conductive member made of a material of low thermal conductivity.

8. The drive unit according to claim 2 , wherein the separator comprises a separation member and a low thermal conductive member provided along the separation member and made of a material of low thermal conductivity.

9. The drive unit according to claim 2 , wherein the separator comprises separation members with a low thermal conductive portion therebetween.

10. The drive unit according to claim 1 , wherein the separator comprises a low thermal conductive member made of a material of low thermal conductivity.

11. The drive unit according to claim 1 , wherein the separator comprises a separation member and a low thermal conductive member provided along the separation member and made of a material of low thermal conductivity.

12. The drive unit according to claim 1 , wherein the separator comprises separation members with a low thermal conductive portion there between.

13. The drive unit according to claim 1 , wherein the heat-sink side fins have a column shape and are arranged lengthwise and crosswise at a predetermined pitch.

14. The drive unit according to claim 1 , wherein the heat-sink side fins are rib shaped fins which are arranged parallel with the flow passage in which the refrigerant passes.

15. The drive unit according to claim 2 , wherein the heat-sink side fins have a column shape and are arranged lengthwise and crosswise at a predetermined pitch and the drive-unit-side fins are rib shaped fins which are arranged parallel with the flow passage in which the refrigerant passes.

16. The drive unit according to claim 15 , wherein the first chamber and the second chamber are in parallel communication with the flow passage.

17. The drive unit according to claim 1 , wherein the first chamber and the second chamber are in parallel communication with the flow passage.

18. The drive unit according to claim 1 , wherein the first chamber and the second chamber are in serial communication with the flow passage.

19. The drive unit according to claim 2 , wherein the heat-sink side fins and the drive-unit-side fins are rib shaped fins which are arranged parallel with the flow passage in which the refrigerant passes with the heat-sink side fins arranged at smaller intervals.

20. The drive unit according to claim 2 , wherein the drive-unit-side fins contact the separator.