Pneumatically operated active vibration damping device having pressure regulating device

A pneumatically operated active vibration damping device interposed between two members of a vibration system for connecting said two members in a vibration damping manner, said active vibration damping device comprising:

• a first and a second mounting member which are spaced apart from each other and are attachable to said two members of said vibration systems, respectively;
• an elastic body elastically connecting said first and second mounting members;
• a working air chamber adapted to apply an oscillating force between said first and second mounting members based on a periodic change of an air pressure in said working air chamber;
• an air piping system which is connected to said working air chamber and which is cooperate with said working air chamber to define a negative pressure applied region;
• a switch valve which is connected to said air piping system and which is operable for connecting said air chamber alternately to a vacuum source and an atmosphere for thereby causing said periodic change of said air pressure in said working air chamber;
• and
• at least one pressure-regulating valve which is connected to said negative pressure applied region and which is operable for introducing said atmosphere into said negative pressure applied region, when a level of said negative pressure in said negative pressure applied region is higher than a predetermined level of said negative pressure, for thereby adjusting said level of said negative pressure applied to said working air chamber.