Gas turbine engine control using plural servomotors

Claim 1

A FLUID-OPERATED SERVOMECHANISM COMPRISING A CASING HAVING SEPARATE COAXIAL MASTER AND SLAVE CYLINDERS, MASTER AND SLAVE PISTONS AXIALLY SLIDABLY MOUNTED IN SAID MASTER AND SLAVE CYLINDERS RESPECTIVELY, EACH PISTON BEING CONNECTED TO A RESPECTIVE SHAFT AND DIVIDING ITS RESPECTIVE CYLINDER INTO TWO CHAMBERS, THE SHAFT OF THE SLAVE PISTON HAVING A BORE IN WHICH THE SHAFT OF THE MASTER PISTON IS SLIDABLY LOCATED, MEANS FOR ROTATING THE SHAFT OF THE MASTER PISTON, A SLAVE MOTIVE FLUID SOURCE AND FIRST AND SECOND CONTROL PRESSURE FLUID SOURCES, FIRST AND SECOND RESTRICTED ORIFICES MEANS PROVIDING IN SAID CASING, SAID SLAVE PISTON MOTIVE FLUID SOURCE BEING CONNECTED TO EACH OF THE TWO CHAMBERS SEPARATED BY THE SLAVE PISTON VIA SAID FIRST RESTRICTED ORIFICE MEANS, AND SAID FIRST CONTROL PRESSURE FLUID SOURCE BEING CONNECTED TO ONE OF THE TWO CHAMBERS SEPARATED BY THE MASTER PISTON VIA SAID SECOND RESTRICTED ORIFICE MEANS, SAID CASING FURTHER HAVING APERTURE MEANS WHEREBY SAID SECOND CONTROL PRESSURE FLUID SOURCE IS CONNECTED TO THE OTHER OF THE TWO CHAMBERS SEPARATED BY THE MASTER PISTON, SAID ONE CHAMBER HAVING BLEED VALVE MEANS CONTROLLED BY THE RELATIVE POSITION OF THE MASTER PISTON IN ITS CYLINDER FOR BLEEDING FROM SAID ONE CHAMBER PRESSURE FLUID ORIGINATING FROM SAID FIRST CONTROL PRESSURE FLUID SOURCE, WHEREBY THE PRESSURE IN SAID ONE CHAMBER IS REDUCED BELOW THE PRESSURE OF SAID FIRST CONTROL PRESSURE FLUID SOURCE, AND THE MASTER PISTON IS ADJUSTED IN ITS CYLINDER TO A RELATIVE POSITION DEPENDING UNIQUELY ON THE RELATIVE PRESSURES OF SAID FIRST AND SECOND CONTROL PRESSURE FLUID SOURCES, THE MASTER AND SLAVE CYLINDERS BEING AXIALLY SEPARATED BY AN EXHAUST CHAMBER CONNECTED TO EXHAUST, SAID SLAVE PISTON AND SHAFT THEREOF HAVING PASSAGEWAYS CONNECTED EACH CHAMBER SEPARATED BY THE SLAVE PISTON TO THE BORE OF THAT SHAFT, THE SHAFT OF THE MASTER PISTON LOCATED IN SAID BORE HAVING MEANS FOR SELECTIVELY CONNECTING ONE OF SAID PASSAGEWAYS TO THE EXHAUST CHAMBER, DEPENDING ON THE DIRECTION IN WHICH THE MASTER PISTON IS ADJUSTED IN ITS CYLINDER, SUCH THAT THE SLAVE PISTON IS ADJUSTED IN THE SAME DIRECTION AS THE MASTER PISTON AS A RESULT OF THE PRESSURES ON OPPOSITE SIDES OF THE SLAVE PISTON BECOMING UNEQUAL DUE TO THE DISCHARGE OF SLAVE PISTON MOTIVE FLUID TO EXHAUST VIA THE SELECTED ONE OF SAID PASSAGEWAYS.