Patent ID: 6408739
Filing Date: 2002-06-25
Classification: F15B,F16F

Abstract:
A pneumatic cylinder with internal hydraulic dampening means, comprising:a pneumatic cylinder barrel having a head on one end thereof and a cap on the opposite end thereof forming an internal pneumatic chamber, the head having a first passage means for passing air into and out of said pneumatic chamber, and the cap having a second passage means for passing air into and out of said pneumatic chamber; a piston rod disposed in the pneumatic chamber so as to be axially movable therein, the piston rod extending outwardly of the head for receiving an impact force; a pneumatic piston mounted on the piston rod in the pneumatic chamber so as to be axially movable with the piston rod in response to air passing into said pneumatic chamber; the pneumatic piston having a cushioning structure facing at least one of the ends of the cylinder barrel; a shock piston slidably moveable on the piston rod and engageable with the cushioning structure to form a cushioning chamber; the pneumatic piston having an internal hydraulic metering passage fluidly connected to the cushioning chamber; a charge of a hydraulic fluid filling the cushioning chamber and the metering passage such that as the pneumatic piston approaches one of the ends of the cylinder barrel, the hydraulic fluid from the cushioning chamber passes through the metering passage, the metering passage being so sized as to exert a resistance to the passage of the hydraulic fluid therethrough, thereby cushioning the motion of the pneumatic piston at the end of a stroke; and the metering passage comprising the pneumatic piston having a first orifice and a second orifice, and the shock piston having a first pin of a first length aligned with the first orifice and a second pin of a second, lesser length aligned with the second orifice, the first pin being receivable in the first orifice to restrict fluid passage through the metering passage, and the second pin being receivable in the second orifice to provide a further flow restriction through the metering passage at a different location of the pneumatic piston along a stroke.