Patent GB-625652-A (GB)
Title: Improvements in and relating to power control systems for internal combustion engines for aircraft
IPC: F02D9/00
Filed: 1945-07-27
Abstract: 625,652. Fluid - pressure servomotor control systems. FISHER, A. D., and MURASZEW, A. July 27, 1945, No. 19328. [Class 135] [Also in Groups XXIV and XXVII] In a power control system for aircraft engines, the boost pressure, engine speed and supercharger speed gear are all selected by the movement of a single manual control member, the arrangement being such that the boost pressure is maintained at its selected value after the throttle is fully open by automatically increasing the engine speed above its selected value to an upper limit corresponding to the said value. This speed increase is effected by the throttle operating device of the boost control. For partial throttle openings, the setting of the manual control member alone determines the selected engine speed. The manual control member also acts directly on the throttle operating means in a direction to open the throttle but except in the idling range, such opening movement is less than that produced by the servo device of the boost control even at sea level in the same position of the manual control member, a spring lost-motion connection between the servo device and the throttle operating means being provided to allow this direct manual operation when the servo device fails in the " throttle closed " position. The gear change is arranged to be made automatically at the most advantageous altitude, i.e. for any part of the power range when the powers developed in the two gears are equal and over the " economical cruising " portion of the power range when the specific fuel consumptions in the two gears are the same. The manual control member also controls the ignition advance and a slow-running cut-out. As shown, the apparatus comprises two housing parts 31, 33, Fig. 7, the upper supporting a camshaft 39, Fig. 13, operated through a rack and pinion in a supplementary housing 32 by a manual control member (not shown). The shaft 39 carries cams 41, 76, 123, 161, 163, all of which have followers carried by rockers supported freely on or coaxial with a fixed rocker shaft 40. The cam 41, Fig. 15, through a rocker 42, carrying an adjustable stud 42a controls the datum of a capsule stack 44 exposed to the boost pressure in a chamber 45. The capsule stack is connected to a piston valve 47 controlling a double acting servopiston 58, Fig. 16, in a cylinder body 187. The rod 59 of the servopiston loosely carries a collar 61 on which is screwed a trunnion sleeve 63 with trunnions 64 engaging the forked end of a rocker 66. The collar 61 is pressed against a nut 60 by a spring 62. The rocker 66 is rigid with a short sleeve 66a, Fig. 13, coaxial with the rockershaft 40. The engine throttle (not shown) is connected to the sleeve 66a by a lever 70 and a rod 199, Fig. 7. The servopiston thus adjusts the throttle so as to maintain the boost pressure selected by the manual control member through the cam 41. A further cam 68 also fast on the shaft 39 operates on a roller 67 carried by the rocker 66 when the servopiston is near the top of its cylinder either due to the manual control member being in the idling range or to the servomotor failing in this position. The throttle movement effected by the cam 68 is limited by a shoulder 59a on the piston-rod 59. Outside, the idling range, the position of the rocker 66 called for by the cam 41 is outside the range of the cam 68. The speed-selecting cam 76, Fig. 17, acts on a double arm rocker 77, 78, loose on the shaft 40. The arm 78 is connected by an adjustable link 81 to a differential link 83, the ends of which are connected to a rocker 87 and a lever 89, the latter connection being through a link 85. The lever 89 has a fixed pivot 90 and is connected by a chain 92 and a cable 202, Fig. 7, to the speed selector lever of a conventional constant speed unit controlling the pitch of the aircraft propeller. The rocker 87 carries a roller 96 engaging a further cam 97, also fast on the shaft 39. The rocker 87 rotates with a countershaft 94 mounted in a bracket 95 and carrying a lever 104, Fig. 20, with an adjustable stop 105 movable up to a fixed stop 106. The tension of the governor spring of the constant speed unit acting through the parts 92, 89, 85, 83, 87, normally maintains the roller 96 off the cam 97 and the stop 105 against the fixed stop 106. The lever 104 is, however, connected by a link 108 with a plunger 110 itself connected through a compression spring 113 and a rod 115 with a lever 117 pivoted at 118 at the base of the cylinder body 187. A screwed rod 120 in the lever 117 is aligned with a tappet 120a in the base of the cylinder of the boost control servopiston 58, nuts 121 limiting the inward movement of this tappet. The spring 113 has little or no compression when the stops 105, 106 are in engagement and the nuts 121 engage the cylinder body 187. When the servopiston 58 approaches its lowest position corresponding to full opening of the throttle, it engages the tappet 120a and through the parts 120, 117, 115, 113, 110, 108, 104, 94 turns the rocker 87 clockwise. This turns the link 83 clockwise and so through the parts 85, 89, 92, 202 increases the speed set by the constant speed unit. so that the selected boost pressure is maintained at full throttle. The clockwise movement of the rocker 87 is, however, limited by the cam 97 which therefore imposes an upper limit to this increase of speed for each position of the manual control member. The spring 113 permits further movement of the servopiston 58 after the roller 96 engages the cam 97. In the idling range, the cam 97 does not permit any movement of the rocker 87. Modified arrangements of the speed control' are described in which the rockers 77, 87 are replaced by a single rocker adjusted by a power piston under the control of a piston valve operated by an extension of the throttle-operating rocker 66. In one of these arrangements, the single rocker has two arms each with a follower roller, one to engage the primary speed-control cam 76 and the other to engage the " modifier " cam 97. In another arrangement the single rocker has one follower roller engageable with the internal or the external surface of a single slotted speed control cam. The pivot 90 and the shaft 94 are adjustable by eccentrics. The point at which the gear change of the engine supercharger is effected depends upon the altitude and can be adjusted by the manual control member through the cam 123, Fig. 21, which engages a rocker 124. The rocker 124 carries an adjustable stud 124a adapted to vary the datum of a capsule stack 126 responsive to atmospheric or air intake pressure in a chamber 127. The capsule stack 126 operates a piston valve 129 controlling a spring-loaded double acting servopiston 138, Fig. 22, connected through a snap-acting linkage 142, 144, 149 to a relay piston valve 151 controlling the hydraulic actuating means of the supercharger change-speed gear. The said linkage comprises a rocker 144 connected with lost motion to the links 142, 149 by.means of slots 145, 146 and having a sharp-nosed cam 147 engaged by a spring pressed roller 157. The valve 151 is retained in its end positions corresponding to low and high gear by a spring-pressed detent engaging grooves 197, 198 respectively. To avoid hunting of the gear changing mechanism near the critical altitude, the lands 130, 131, Fig. 21, of the piston valve 129 are made slightly wider than, or are spaced apart either somewhat more than or less than the conduits 133, 134 they control. The ignition advance is controlled by the manual control member by the cam 161, Fig. 24, having cam profiles 161b, engaging a roller 162a on a rocker 162. The latter is rigid with a short sleeve 162b, Fig. 13, carrying a lever 69 connected through a linkage 200, 201, Fig. 7, with the ignition timing mechanism. The slow running cut-out mechanism is operated by a cam 163, Figs. 13, 25 at the low power end of the travel of the manual control member, this cam acting on said mechanism through a rocker 164, an adjustable link 166, levers 168, 170 on a countershaft 169 and a link 205, Fig. 7. The effective torque of the cams 41, 76, 123, 161, 163 for each position of the manual control member is balanced by a cam 171 with a spring-pressed follower roller. The studs 42a, 124a are eccentrically mounted in adjustable screw plugs such as 124b, Fig. 21, which can be locked in their adjusted positions. These adjustments and that of the trunnion sleeve 63, Fig. 16, are effected through inspection covers 188, 190, 192. The valves 47, 129, 151 are mounted in a common valve body 179 with common pressure and exhaust channels 50, 51, the latter also being connected through a pipe 183, Fig. 13, to the rocker shaft 40 to lubricate the same.