Actuator of diaphragm type

Abstract

An actuator (1) of a diaphragm type which comprises an actuator case (2,3), a diaphragm (5) housed in the actuator case, a diaphragm plate (4) attached to the diaphragm for moving together with the diaphragm according to introduction of negative or atmospheric pressure into a negative pressure chamber (7) formed between the diaphragm and the actuator case (2) so as to actuate a device connected to the diaphragm plate. The diaphragm is formed with one or both of an annular rib (5e) having a thick-walled section and an annular expansive portion (5d) having a curved section. Therefore, the diaphragm is hard to be disengaged from the diaphragm plate even if an immoderate force is applied on the diaphragm.

What is claimed is: 
     
       1. An actuator of a diaphragm type for controlling a device mounted on an automotive vehicle, comprising: an actuator casing having first and second cup-shaped casing halves engaged with each other, the second casing half having an opening through a center part thereof;   a diaphragm disposed between said first and second casing halves of said actuator casing and forming a negative pressure chamber together with said first casing half of said actuator casing, said diaphragm having a plate fitting portion in a center part thereof, said plate fitting portion having a center aperture therethrough .[.and a annular rib surrounding the center aperture.].;   a diaphragm plate disposed in the actuator casing and secured to said plate fitting portion of said diaphragm, said diaphragm plate having a projecting portion with a cable connecting member projecting through the opening in said second casing half of said actuator casing;   a conical spring disposed between said diaphragm plate and said first casing half of said actuator casing, said conical spring urging said diaphragm plate and said plate fitting portion toward said second casing half of said actuator casing; and   said diaphragm further having an annular expansive portion having a semicircularly curved section extending toward said second casing half and located adjacent to the plate fitting portion and spaced from said diaphragm plate to form an air space with said diaphragm plate. .Iadd.2. An actuator of a diaphragm type as set forth in claim 1, wherein said diaphragm further includes an annular rib surrounding the annular expansive portion. .Iaddend.