Patent GB-1082705-A (GB)
Title: Gas turbine engine control system
IPC: F02C9/16
Filed: 1966-07-07
Abstract: 1,082,705. Controlling helicopter rotors. GENERAL MOTORS CORPORATION. July 7, 1966 [Aug. 11, 1965], No. 30470/66. Heading B7G. [Also in Division F1] A gas turbine engine comprises a turbine 7 driving the compressor 5 of the engine, and a turbine 9 driving a helicopter rotor R. The fuel supply to the combustion equipment 6 is controlled by a metering valve 18 under the control of a fuel controller 29 comprising a centrifugal governor 31 driven by the turbine 7 and acting through a lever 54 to tend to open a half-ball bleed valve 57 in a line 46 downstream of an orifice 45 connected to a pressure air manifold 40. The line 46 is connected to the space between a large bellows 47 and a small evacuated bellows 49. A further lever 59, pivoted on the same fulcrum 55 as the lever 54, controls a further halfball valve 61 in a line 43 downstream of an orifice 42 connected to the manifold 40. The line 43 is connected to the outside of bellows 47. The lever 54 is connected by a light spring 65 to an extension 63 of the lever 59 whereby an abutment 66 on the lever 54 contacts the lever 59 at speeds of the turbine 7 below a predetermined value. When the speed reaches this predetermined value, the governor 31 rocks the lever 54 against the action of the spring 65 until a second abutment 67 contacts the lever 59. This rocking motion opens the valve 57 to cause the bellows 47, 49 to open the metering valve 18, thereby increasing the fuel supply to accelerate the turbine 7. At some higher speed, a spring 73 is overcome and the lever 59 is also rocked, thereby opening the valve 61 to allow expansion of the bellows 47, 49 and thereby reduce the fuel supply. The turbine 7 is thus governed to run at this speed, which may be made variable by providing the spring 73 with a movable abutment 71 controlled manually through a lever 69 and cam 70. The manifold 40 supplying air to this governing system is connected through an orifice 39 to a line 38 conveying air from the compressor discharge. A vent valve 41 responsive to atmospheric temperature modifies the pressure in the manifold 40 in accordance with atmospheric temperature. The fuel control is therefore influenced by the compressor discharge pressure and the atmospheric temperature. For controlling the power turbine 9, a pressure regulating valve 81 connected between the line 38 and a line 82 establishes a reference pressure in the latter at a fixed level above atmospheric pressure. The pressure in a line 79 connected to the line 82 through an orifice 83 is governed in accordance with the speed of the turbine 9 by means of a half-ball bleed valve 78 actuated by a centrifugal governor 34, the force of the biasing spring 75 being adjustable by a manual speed control lever 77. An accumulator 85 retards the response to changes of speed. The lines 79, 81 are connected to opposite sides of a diaphragm 86. If the turbine 9 departs from the set speed the valve 78 varies the pressure in line 79 and the diaphragm 86 acts through a push rod 87 to adjust the valve 61 and thereby vary the fuel supply to restore the speed to the set value. When the pilot increases the collective pitch of the rotor R through a control lever 16, the resultant increase of load tends to reduce the speed of turbine 9, thereby eventually causing valve 61 to increase the fuel supply. To provide a quicker response to the need to increase the fuel supply, an anticipator A is provided. When the control lever 16 is moved to increase the collective pitch to 60% or more of the full pitch at a time when the power output is, say, approximately 5 to 10% of rated engine power, a cam 101 connected to the lever 16 compresses a spring 107 sufficiently to overcome the oil pressure exerted on a bellows 106 through a line 103 by a torque meter which measures the driving torque transmitted through a gearbox 13. A stem 111 then moves to the left, opening a valve 112 to connect the line 103 to a drain 136 to prevent subsequent increase in torque from overriding this action. The stem also acts through levers 114, 117 to open a valve 127 and close a valve 131, thereby disconnecting the diaphragm 86 from the line 82 and connecting it instead to atmosphere. This removes the bias exerted on the valve 61 by the push rod 87, and the fuel supply consequently increases. The inertia of the rotor R prevents any consequential radical overspeed of the turbine 9, and there will normally be some decrease of speed because of the time lag for accelerating the turbine 7. The resultant increase of pressure in line 79 compresses a bellows 119 which acts through a rod 118 to override the spring 107 and restore the anticipator A to its normal inoperative condition.