| 摘要 |
At the downstream side of the intake throttle valve 30 of the intake pipe is provided a valve seat 32 serving as the end of the exhaust gas recirculation passage 27. Tile valve element 29 of the EGR valve opens and closes the valve seat 32. The valve element 29 is driven by the balance between the force due to the differential pressure between the negative pressure chamber 42 and atmospheric pressure chamber 43 acting on the diaphragm 39 and the biasing force of the spring 62. Tile pressure of the negative pressure chamber 42 is controlled by a servo valve 46 which consists of a valve element 46a in a cylindrical member 45. That is, when the valve element 46a of the servo valve 46 is displaced in the vertical direction through a screw transmission device by the stepping motor 53, the pressure in the negative pressure chamber 42 changes and the diaphragm 39 displaces. The cylindrical member 45 integral with this follows the valve element 46a and moves until the balance is restored. The EGR valve can be driven by an inexpensive, compact stepping motor, which has a large size and large allowable flow rate, and has a high precision of opening and response to control. |
