Variable pitch propeller control system

Claim 1

A CONTROL SYSTEM FOR THE CONTROL OF THE PITCH ANGLE OF A VARIABLE-PITCH PROPELLER BLADE OF AN AIRCRAFT, THE SYSTEM COMPRISING A PISTON DISPLACEABLE IN A CYLINDER AND OPERATIVELY CONNECTED TO CONTROL, BY THE POSITION OF THE PISTON, THE PITCH ANGLE OF THE PROPELLER BLADE, A DECREASEPITCH LINE COMMUNICATING WITH THE CYLINDER ON ONE SIDE OF THE PISTON FOR THE SUPPLY OF WORKING LIQUID THERETO TO DISPLACE THE PISTON IN ONE DIRECTION IN THE SENSE TO DECREASE THE FORWARD PITCH ANGLE AND INCREASE THE REVERSE PITCH ANGLE OF THE PROPELLER BLADE, AN INCREASE-PITCH LINE COMMUNICATING WITH THE CYLINDER ON THE OTHER SIDE OF THE PISTON FOR THE SUPPLY OF WORKING LIQUID UNDER PRESSURE TO DISPLACE THE PISTON IN THE DIRECTION OPPOSITE TO SAID ONE DIRECTION IN THE SENSE TO DECREASE THE REVERSE PITCH AND INCREASE THE FORWARD PITCH OF THE PROPELLER BLADE, MECHANICAL STOP MEANS NORMALLY DEFINING A LIMITING DISPLACEMENT OF THE PISTON IN SAID ONE DIRECTION, SELECTING MEANS DISPLACEABLE THROUGH A SERIES OF POSITIONS TO SELECT THE DESIRED VALUES OF THE PROPELLER SPEED AND OF THE PITCH ANGLE OF THE PROPELLER BLADE, THE SELECTING MEANS HAVING TWO SUCCESSIVE RANGES OF POSITIONS THE FIRST OF WHICH CORRESPONDS TO PISTON POSITIONS DISPLACED FROM SAID LIMITING DISPLACEMENT IN THE DIRECTION OPPOSITE TO SAID ONE DIRECTION AND THE SECOND OF WHICH CORRESPONDS TO PISTON POSITIONS DISPLACED FROM SAID LIMITING DISPLACEMENT IN SAID ONE DIRECTION, A CONTROL LINE ARRANGED FOR THE SUPPLY OF OPERATING LIQUID AT A PRESSURE WHICH CAN BE VARIED, FIRST HYDRAULIC-VALVE MEANS CONTROLLED BY THE PRESSURE IN THE CONTROL LINE AND ARRANGED, WHEN THAT PRESSURE IS LESS THAN A FIRST LIMITING VALUE, TO PREVENT SAID WORKING LIQUID FROM BEING DISCHARGED FROM THE CYLINDER TO THE INCREASE-PITCH LINE, SECOND HYDRAULICI-VALVE MEANS ALSO CONTROLLED BY THE PRESSURE IN THE CONTROL LINE AND ARRANGED, WHEN THAT PRESSURE EXCEEDS A SECOND LIMITING VALUE GREATER THAN THE FIRST LIMITING VALUE, TO RENDER THE STOP MEANS INOPERATIVE, A PRESSURE-SETTING RELIEF VALVE CONNECTED TO SAID CONTROL LINE AND ARRANGED TO VARY THE PRESSURE OF THE LIQUID WITHIN THE CONTROL LINE AND TO CONTROL THAT PRESSURE TO A VALUE INTERMEDIATE SAID FIRST AND SECOND LIMITING VALUES WHEN THE SELECTING MEANS IS WITHIN SAID FIRST OF ITS TWO RANGES, MEANS OPERABLE BY THE SELECTING MEANS WHEN WITHIN SAID SECOND OF ITS TWO RANGES TO NORMALLY CAUSE THE RELIEF VALVE TO CONTROL THE PRESSURE OF THE LIQUID WITHIN THE CONTROL LINE TO A VALUE GREATER THAN BOTH SAID FIRST AND SAID SECOND LIMITING VALUES, A DIFFERENTIAL DEVICE OPERABLY CONNECTED TO SAID SELECTING MEANS AND THE PROPELLER BLADE WHEN THE SELECTING MEANS IS WITHIN SAID SECOND OF ITS TWO RANGES TO PROVIDE A MOVEMENT WHICH IS A FUNCTION OF THE PITCH ANGLE ERROR OF THE PROPELLER BLADE, A MECHANICAL LINKAGE OPERABLY CONNECTED BETWEEN SAID DIFFERENTIAL DEVICE AND SAID RELIEF VALVE TO CAUSE THAT VALVE TO CONTROL THE PRESSURE OF THE LIQUID WITHIN THE CONTROL LINE TO A VALUE LESS THAN BOTH SAID FIRST AND SECOND LIMITING VALUES WHEN THE DEPARTURE OF THE PISTON POSITION IN SAID ONE DIRECTION FROM A SELECTED POSITION EXCEEDS A PREDETERMINED VALUE, AND CLUTCH MEANS OPERATED BY THE SELECTING MEANS TO DISENGAGE THE MECHANICAL LINKAGE FROM THE RELEIF VALVE EXCEPT WHEN THE SELECTING MEANS IS WITHIN SAID SECOND OF ITS TWO RANGES.