the following is a list of main features of an embodiment of the invention to be described hereinbelow . feature 1 : a semiconductor device which generates heat when operating is disposed on an outside surface of a top panel of a heat exchanger body . a liquid coolant flows through the heat exchanger body . the semiconductor device is cooled with the liquid coolant . feature 2 : an upper limit of output power from the semiconductor device is set according to the detected temperature of the liquid coolant thereby preventing the overheating of the semiconductor device . if the temperature detection has low accuracy , the upper limit must be set to a lower value because a substantial margin need be allowed for the upper limit . if the temperature detection is increased in accuracy , the margin allowed for the upper limit can be reduced so that the value of the upper limit can be increased . increase in the accuracy of temperature detection leads to the expansion of operating range of the semiconductor device . feature 3 : the semiconductor device regulates electric power supplied to a traction motor . the increase in the operating range of the semiconductor device leads to improvement of the travelling performance of the vehicle . feature 4 : a wall of a casing accommodating an electronic device which generates heat when operating abuts on a bottom panel of the heat exchanger body . fig2 shows , in perspective , the vicinity of a heat carrier inflow pipe 22 of the heat exchanger body 7 . fig1 is a sectional view taken on the line i - i in fig2 . in fig1 and fig2 , a reference numeral 6 denotes a bottom panel ; a reference numeral 8 denotes a top panel ; a reference numeral 10 denotes a bracket ; a reference numeral 12 denotes a bolt ; a reference numeral 14 denotes a nut ; a reference numeral 16 denotes a temperature sensor support board ; a reference numeral 18 denotes a temperature sensor ; a reference numeral 20 denotes a cable for transmitting an output from the temperature sensor to an external device . a reference numeral 4 denotes a heat carrier passage . a reference numeral 2 denotes a casing . a semiconductor device which generates heat when operating is fixed to an unillustrated area of an outside surface of the top panel 8 via a board formed of a material which has electrical insulative properties and high heat conductivity . accommodated in the casing 2 is an electronic device which generates heat when operating . a liquid coolant flows through the heat carrier passage 4 , cooling the semiconductor device in contact with the top panel 8 as well as cooling a wall of the casing 2 in contact with the bottom panel 6 . the top panel 8 and the bottom panel 6 are formed from an aluminum alloy having high heat conductivity . in this embodiment , the heat exchanger body 7 is a cooler body , the heat carrier is the liquid coolant , and the heat carrier passage 4 is a liquid coolant passage . it is to be noted , however , that the fixing structure for the temperature sensor according to the embodiment is not only effective in cooling operation but also effective in heating operation using the heat carrier . further , the temperature sensor fixing structure of the embodiment is also effective for a case where the heat carrier is gaseous . as shown in fig1 , the top panel 8 is flat while the bottom panel 6 is curved . the heat carrier passage 4 is formed by superposing the top panel 8 on the bottom panel 6 , followed by brazing overlapped opposite ends thereof . overlapped areas of the top panel 8 and the bottom panel 6 are formed with a plurality of through - holes 24 . bolts 25 penetrating through these through - holes are screwed into the wall of the casing 2 thereby fixing the heat exchanger body 7 to the casing 2 . fixing the heat exchanger body 7 to the casing 2 brings the bottom panel 6 into intimate contact with the casing 2 . indicated at 27 in the figure is a sleeve . a bracket 10 is brazed to the outside surface of the top panel 18 in order to fix the temperature sensor 18 to the top panel 8 . the bracket 10 is formed with a stepped through - hole 10 a for receiving a head and a shank of the bolt 12 . the bolt 12 is press - inserted into the through - hole 10 a . the head of the bolt 12 is brazed to the top panel 8 in conjunction with brazing the bracket 10 to the outside surface of the top panel 8 . the shank of the bolt 12 extends upward from the bracket 10 . the temperature sensor 18 is a thermistor and is fixed to the temperature sensor support board 16 . the temperature sensor support board 16 is formed with a through - hole 16 a which allows the shank of the bolt 12 to penetrate therethrough . after the shank of the bolt 12 is inserted through the through - hole 16 a of the temperature sensor support board 16 , the nut 14 is screwed on the bolt 12 . when the nut 14 is screwed on the bolt 12 , the nut 14 presses down the temperature sensor support board 16 onto the bracket 10 , thus fixing the temperature sensor support board 16 to the top panel 8 . the bracket 10 , bolt 12 and temperature sensor support board 16 are formed from aluminum alloy having high heat conductivity . when the temperature sensor 18 is fixed to the top panel 8 via the temperature sensor support board 16 by using the bracket 10 , bolt 12 and nut 14 , the temperature sensor 18 is disposed at an area deviated from a position to face the heat carrier passage 4 via the top panel 8 . the bracket 10 and the bolt 12 fixed to the bracket 10 are disposed at positions to face the heat carrier passage 4 via the top panel 8 . as shown in fig1 , the bolt 12 is disposed at the position to face a central part of the heat carrier passage 4 via the top panel 8 . furthermore , the top panel 8 is thinner than the bottom panel 6 . the main heat transfer passage from the heat carrier in the heat carrier passage 4 to the temperature sensor 18 goes from the heat carrier in the heat carrier passage 4 → the top panel 8 → the bolt 12 → the temperature sensor support board 16 → the temperature sensor 18 . the length of the heat transfer passage from the heat carrier in the heat carrier passage 4 to the temperature sensor 18 is minimized . the position of the through - hole 16 a formed in the temperature sensor support board 16 is deviated from the fixing position of the temperature sensor 18 . hence , the temperature sensor 18 is deviated from the position to face the heat carrier passage 4 via the top panel 8 . even so , the temperature sensor 18 involves less detection error and detection delay because the main heat transfer passage is short in length . in the case shown in fig3 , the temperature sensor 18 faces the heat carrier passage 4 via the top panel 8 . at first glance , the structure of fig3 is more adapted for the exact and quick detection of the temperature of the heat carrier by means of the temperature sensor 18 . actually , however , the structure of fig1 is more adapted for the exact and quick detection of the temperature of the heat carrier . the reason is that the temperature sensor 18 of fig1 or the temperature sensor 18 of fig3 is not in intimate contact with the bracket 10 nor the top panel 8 and hence , the amount of heat transmitted to the temperature sensor 18 is low . it was found that what is important is to reduce the length of the heat transfer passage including metal - to - metal intimate contact so as to be capable of transferring a large amount of heat . in the case shown in fig1 , the heat transfer passage from the heat carrier in the heat carrier passage 4 to the temperature sensor support board 16 is minimized in the length and hence , the structure of fig1 is adapted to detect the temperature of the heat carrier more exactly and quickly than the structure of fig3 . according to the embodiment , the heat transfer passage going from the heat carrier in the heat carrier passage 4 → the top panel 8 → the bolt 12 → the temperature sensor support board 16 → the temperature sensor 18 is spaced farther away from the wall of the casing 2 than the heat transfer passage shown in fig3 . therefore , the influence that the heat of the wall of the casing 2 exerts on the temperature sensor 18 is reduced . with the additional effect of the reduced influence of the heat of the wall , the structure of the embodiment is adapted for the exact and quick detection of the temperature of the heat carrier by means of the temperature sensor 18 . in the above - described embodiment , the temperature sensor support board 16 is pressed down onto the bracket 10 by screwing the nut 14 on the bolt 12 anchored in the bracket 10 . alternatively , a screw hole may be formed in the bracket 10 and the bolt may be screwed into the screw hole so as to permit the head of the bolt to press down the temperature sensor support board 16 onto the bracket 10 . a shaft member fixed in the bracket may be the shank of the bolt 12 anchored in the bracket 10 or the shank of the bolt screwed into the bracket 10 . a pressing member for pressing down the temperature sensor support board 16 on the bracket 10 may be the nut 14 or the head of the bolt . the combination of bolt and nut may be replaced by a rivet drivenly fixed in the bracket 10 . the temperature sensor support board 16 can be pressed down onto the bracket 10 with a head of the rivet . the shaft member may be formed integrally with the bracket . although the specific examples of the invention have been described in detail , these examples are intended for purposes of illustration only and are not intended to limit the scope of the appended claims . the techniques disclosed in the scope of the claims include various modifications and changes of the above examples . further , the technical elements described in this specification or shown in the drawings deliver technical utilities as used alone or in various combinations thereof and hence , are not limited to the combinations stated in the claims of this patent application . the techniques illustrated in this specification or the drawings are intended to achieve a plurality of purposes at a time and hence , deliver the technical utility by achieving any one of these purposes .