Electronic control device

1. An electronic control device for controlling an electric actuator, comprising:

a casing fixable to an actuator housing of the electric actuator;

a circuit board accommodated in the casing, on which electronic parts including a heat generating part are installed;

a projecting portion projecting from an inside surface of the casing, a region of the circuit board in which the heat generating part is installed being seated on the projecting portion;

an air passage formed between the inside surface of the casing, the circuit board and an outer peripheral surface of the projecting portion;

a vent hole extending through the casing to communicate the air passage and an outside of the casing with each other; and

a communication hole extending through the casing such that when the casing is fixed to the actuator housing, an inside space of the actuator housing and the air passage are communicated with each other through the communication hole,

wherein the air passage allows air to flow between the vent hole and the communication hole when the electric actuator is driven in a state that the casing is fixed to the actuator housing.

2. The electronic control device as claimed in claim 1 , wherein the casing comprises an open ended case in which the circuit board is accommodated, and a cover that covers an open end of the case, the casing being mountable to the actuator housing in such a state that a bottom wall of the case faces to the actuator housing,

wherein the projecting portion projects from the bottom wall of the case,

wherein the communication hole extends through the bottom wall of the case, and

wherein the circuit board comprises a connecting portion that electrically connects the circuit board and the electric actuator with each other, the connecting portion projecting from the circuit board toward the bottom wall of the case and extending through the communication hole.

3. The electronic control device as claimed in claim 2 , wherein the electronic parts comprise a noise filter part that reduces noise, the noise filter part being installed on a surface of the circuit board which faces to the bottom wall of the case, the air passage being formed between the noise filter part and the outer peripheral surface of the projecting portion.

4. The electronic control device as claimed in claim 1 , wherein the heat generating part is a switching element that is operated to drive the electric actuator.

5. The electronic control device as claimed in claim 2 , wherein the communication hole is formed into a slit shape extending along a corner portion at which the outer peripheral surface of the projecting portion and the bottom wall of the case are encountered with each other.

6. The electronic control device as claimed in claim 2 , wherein the projecting portion is contacted with a side peripheral wall of the case which has a plurality of cooling fins on an outer surface thereof.

7. The electronic control device as claimed in claim 2 , wherein the bottom wall of the case is formed with a plurality of supporting portions extending from the bottom wall toward the cover, the supporting portions being exposed to the air passage between the vent hole and the communication hole.

8. The electronic control device as claimed in claim 2 , wherein the heat generating part and the projecting portion on which the heat generating part is seated are contacted with each other through a heat conductive material.