Patent ID: 8453557

Claim:
A piston actuator assembly comprising: a housing having a bore, a first and a second apply passage and a first and a second exhaust passage, wherein the bore has an inner surface, an open end and a closed end; a piston slidably disposed in the bore of the housing, wherein the piston has a head portion and a connecting rod portion, wherein the head portion has a first and a second apply surface area and the connecting rod portion extends through the open end of the bore of the housing; a piston liner slidably disposed in the bore of the housing between the housing and the head portion of the piston, wherein the piston liner has a bore, a first and a second end, an inner and an outer surface and a liner apply surface area; a seal assembly disposed in the open end of the housing bore, wherein the seal assembly includes a sealing surface, a center bore, and an annular channel, wherein the connecting rod portion is sealingly supported by the sealing surface and the annular channel is in communication with the center bore and the first exhaust passage of the housing; a first hydraulic fluid chamber, wherein the first hydraulic fluid chamber is defined by at least the inner surface of the bore of the housing and the first apply surface area of the head portion of the piston, wherein the first apply passage communicates with the first hydraulic fluid chamber; a second hydraulic fluid chamber, wherein the second hydraulic fluid chamber is defined by at least the inner surface of the bore of the housing, the liner apply surface area of the piston liner, the second apply surface area of the head portion of the piston and the sealing surface of the seal assembly, wherein the second apply passage communicates with the second hydraulic fluid chamber, and wherein the hydraulic passages are selectively pressurized to move the head of the piston into at least three positions, wherein a first position is defined by the head of the piston adjacent the closed end of the bore of the housing, a second position is defined by the head of the piston adjacent the seal assembly, and a third position is defined by the head of the piston disposed approximately midway between the closed end of the bore of the housing and the seal assembly.