Patent GB-1131840-A (GB)
Title: Gas turbine engine
Inventor: CROSS WALTER GEORGE
IPC: F02K1/15
Filed: 1966-11-16
Abstract: 1,131,840. Gas turbine jet propulsion plant. ROLLS-ROYCE Ltd. Nov. 16,1966, No. 51443/66. Heading F1J. [Also in Division G3] A gas turbine engine has a variable area propulsion nozzle, apower operated devicefor varying the area of the nozzle and a device responsive to a pressure functionally related to a pressure in the engine jet pipe, the pressure responsive device and/ or means associated therewith, on a predetermined variation in the jet pipe pressure, causing the power operated device to adjust the nozzle area to compensate for the variation at a rate which is large in comparison with the change in the jet pipe pressure, the rate at which the nozzle area is adjusted being gradually reduced with time. The nozzle area control mechanism comprises, Fig. 2, several rams 26 connected through links 31 with an axially movable sleeve (32), Fig. 1 (not shown), surrounding the jet pipe (16). The downstream end (33) of the sleeve is frusto-conical and engages rollers (36) on the nozzle flaps (34) so that axial movement of the sleeve varies the nozzle area. Each ram 26 includes a piston 30 having a highpressure side 30A supplied with actuating oil from an engine driven swash-plate pump 43. The angle of the swash-plate 44, and thus the pump output, is varied according to changes in the ratio of a pressure functionally related to the compressor outlet pressure P 3  to a pressure functionally related to the jet pipe pressure P 6  and sensed by a piston 66. An increase in the pressure P 6 , resulting for example from commencement of reheat in the jet pipe, causes piston 66 and an integral rod 65 to move to the right permitting leak off of highpressure fuel through drilling 75, 76 in the rod from side 61 of a servopiston 56 integral with a sleeve 54 slidably surrounding rod 65, and consequent movement to the right of piston 56. A vent 82 to atmosphere controlled by a very gradually tapered needle 86 of high gain forming an extension of rod 65 enables the initial movement of piston 66 to be rapid and large for small changes in the ratio P 3 /P 6 . The movement of piston 56 is communicated to the swash-plate 44 by way of links 53, 49 and 47 to thus reduce pump output and cause ram piston 30 to move downwardly to allow the nozzle to open rapidly under internal gas pressure and reduce P 6 . The fulcrum of link 49 consists of a roller 51 running in a track 50 in the link and carried by an arm 110 attached to an arm 111 of a bellows device 112. Arm 111 has at its upper end a roller 113 running in a track 114 in a housing 104 and at its lower end a beam 124 and a track 123 engaging a roller 122 forming a pivotal mount for a second beam 115. A spring 115A urges the left side of beam 115 into engagement with a bellows 116 responsive to changes in the pressure difference across a restriction 90 in the oil line 91 leading from a backing pump 92 to the low-pressure side of the swash-plate pump 43. A similar bellows 117 acts on the right side of beam 115 and is responsive to changes in the pressure difference across a restriction 94 in the oil return line 41. The arrangement is such that immediately ram piston 30 moves downwardly on in increase in P 6 , as described, there is an inflow of oil to side 30B of the piston thus decreasing the flow and pressure drop through restriction 94 and causing bellows 117 to expand and pivot beam 115 anti-clockwise. Beam 124 thus rises taking with it movable fulcrum 51 of link 49 and increasing the output of pump 43 so that the rate of movement of the ram piston 30 and the rate of opening of the nozzle are gradually reduced. Bellows 116 acts to adjust the datum position of beam 115 in response to small changes in the oil flow through restriction 90. A duct 97, communicating with oil line 41 between non-return valves 95, 96, extends to the throat of a Venturi 98 within a chamber 100 containing the oil tank 93. The throat of the Venturi 98 communicates via a duct 101 with the interior of the oil tank 93 so that whenever there is a flow of oil through the duct 97 oil and air will be drawn from the tank into the chamber 100. In a modification, Fig. 3 (not shown), linkage 47, 49, 53 is replaced by a direct connection (125) between the servopiston (56A) and the swash-plate (44A). The side of the piston (66A) subject to a function of P 3  communicates through a passage (130) with a large chamber (131) which has the effect of permitting the piston (66A) to move further and initially faster for a given change in P 6  than would have been the case without the chamber (131). A non-return valve may be provided adjacent the passage (130) to permit rapid opening of the nozzle if P 3  collapses as a result of compressor surging. In a further modification, Fig. 4, the chamber (131) is replaced by a vent passage 145 controlled by a valve 144 connected by a spring-loaded rod 143 to a dashpot cylinder 140. A piston 135 is slidably mounted in the cylinder 140 and connected by rod 134 to an arm 132 on the sleeve 54B of the servopiston 56B. Springs 140, 141 urge piston 135 to a central position. Thus, when an increase in P 6  moves piston 66B to the left, cylinder 140 also moves to the left causing vent 145 to open, initially reducing the pressure on side 71B of the piston and making the movement more rapid. Spring 146 then moves valve 144 towards the closed position to increase pressure on the side 71B so that piston 66B moves back towards the equilibrium position to increase the output of pump 43B and thus gradually reduce the rate of opening of the nozzle. In a further modification, Fig. 6 (not shown), a vent passage (162), similar to vent 145 is controlled by a valve (163) connected to a bellows (164) responsive to jet pipe pressure P 6 . In a further modification, Fig. 5, the servopiston 56C is connected by a rod 54C to a cylinder 156 of a dashpot device 157 containing a piston 155 centred by springs 160, 161. The piston 155 is connected by a link 154 to a pivoted beam 151 connected in turn to the swashplate 44C. An increase in P 6  causes movement of piston 66C to the left accompanied initially by a full corresponding movement of the swash-plate 44C against the action of spring 153 to give a rapid increase in nozzle area. Subsequently after a period determined by the dashpot 157, the spring 153 will gradually return the swash-plate 44C to reduce the rate of opening of the nozzle. In a further modification, Fig. 7 (not shown) the initial rapid rate of opening of the nozzle with subsequent gradual reduction is achieved by the vent (83E) from the P 3  chamber being controlled by a tapered needle having a cylindrical portion (174). Thus a sudden increase in P 6  causes full leftward movement of the piston (66E) with corresponding adjustment of the swash-plate (44E) to reduce the pump output. As the nozzle opens P 6  begins to fall so that the piston (66E) gradually moves back towards its equilibrium position and the rate of opening of the nozzle is reduced.