Patent GB-703910-A (GB)
Title: Improvements in or relating to control mechanisms for supercharged reciprocating internal combustion engines for aircraft
Inventor: WEBB RICHARD HARVEY
IPC: F02D9/00
Filed: 1950-07-06
Abstract: 703,910. Fluid-pressure servomotor-control systems. ROLLS-ROYCE, Ltd. Sept. 28, 1951 [July 6, 1950], No. 16968/50. Class 135. [Also in Group XXVII] The invention relates to automatic boost control apparatus for supercharged internal combustion engines on aircraft of the kind comprising a pressure responsive device such as the aneroid capsule 40 which actuates the control valve 43 of a servomotor having a servo-piston 45 movable between " open stop " and closed stop " positions to adjust the throttle valve 9 of the supercharger in co-operation with the pilot's engine control lever 10, which control lever is also arranged to adjust a cam 48 acting on the servo-control valve 43 to select a datum-boost. According to the invention, the linkage interconnecting the throttle valve 9, the control lever 10, and the servo-piston 45 is such that (a) with the servopiston in the " open stop " position, Fig. 1, movement of the control lever 10 over the greater part of its range of movement causes only a small angular movement of the throttle, such movement being substantially in the dead range of movement of the throttle valve, that (b) with the control lever 10 fixed, movement of the servopiston between its stops effects a large angular movement of the throttle valve, and that (c) with the control lever in the closed position (that is, its idle setting) and the servo-piston in the " closed stop" position, the throttle valve 9 is substantially closed, and also according to the invention, the datum adjusting cam 48 is so shaped that for settings of the control lever 10 on the throttle closed side of a setting selected to correspond substantially with the lower end of the cruising range, the datum boost is less than the boost obtainable with the servo-piston in the closed stop position and that for control lever settings above the selected setting, the datum boost is greater than that obtainable with the servo-piston in the closed stop position. Such an arrangement avoids to a large extent necessity of " hand feeding" of the throttle at high altitudes. The invention may be used in conjunction with an automatic ignition timing device 12 of the type comprising a mechanism operated by the pilot's control lever to set the ignition timing of the engine to a value dependent on the posiion of the lever. Usually the ignition timing is fully advanced over the cruising range but is gradually retarded to a value about halfway between the fully advanced and the fully retarded positions as the control lever moves to the maximum power setting. As " hand-feeding " of the throttle at high altitudes is largely avoided, the undesirable retardation of the ignition timing in the cruising range consequent on " hand-feeding " of the throttle is also avoided. The control lever 10 is connected to a crossshaft 25 through a link 27 and a radius arm 26. The shaft 49 of the datum adjusting cam 48 is connected to the shaft 25 through a link 51 and radius arm 50. The throttle valve 9 which may be in the inlet or the outlet of the supercharger is connected to the cross-shaft 25 through a link 54, a radius arm 55, and the differential gear 8. The servo-piston 45 which is loaded by a spring 47 is similarly connected to the shaft 25 through a link 52, a radius arm 53, and the differential gear 8. The latter comprises bevel sun gears 8a 8b the hubs of which are rigid with the arms 53, 55 respectively, and a planet gear 8c carried on an arm 56 rigid with the cross shaft 25. The full movement of the lever 10 is about 70 degrees and of the arm 26 about 12 degrees. Such movement results in a movement of the arm 55 of about 24 degrees and of the throttle valve 9 of about 14 degrees. With the control lever 10 fixed, full movement of the servo-piston 45 results in a movement of the arms 53, 55 of about 55 degrees and of the throttle valve of about 32 degrees. The throttle valve 9 and the arm 55 may be arranged to have equal angular movements. The aneroid capsule. 40 is exposed to the induction pipe pressure through a pipe 42. The cam 48 acts on the control valve 43 through a spring 43a. The automatic ignition timing device 12 comprises a shaft 13 driven from the engine crankshaft through gearing 15, 16 and splined to a hollow shaft 14 in driving connection with the magneto drive-shaft 18 through a worm 14a and a worm wheel 17. The shaft 14 is connected through a ball thrust bearing 20 to the piston rod 19b of a spring-loaded servopiston 19a operating a cylinder 19. The spaces 33, 34 on opposite sides of the piston 19a are connected through a restriction 37. Pressure fluid is supplied to the space 33 to move the servo-piston 19a in a direction to advance the ignition timing under the control of a valve comprising an inner sleeve 21 with a radial port 22 and an outer sleeve 28 with a wider port 29 the latter being connected through a casing 31 and a pipe 32 to the space 33. Pressure fluid is supplied to the interior of the sleeve 21 which is driven from the cross-shaft 25 through a bevel gear 24 and a toothed quadrant 23. In the closed position of the lever 10, the ports 22, 29 are not in communication, but on movement of the control lever to open the throttle valve, the port 21 moves into register with the port 29 so as to advance the ignition timing to the " full advance position at the same time, the servopiston 19A due to the pin-and-slot connection 30 moves the port 29 in the opposite direction to the port 22 to increase the degree of register between the two ports. On still further movement of the throttle, the port 22 is cut off from the port 29 to retard the ignition timing and the piston 19a then moves the port 29 in the same direction as the port 22 which is therefore uncovered again. In a modification, the datum varying cam 48 moves the control valve 43 positively through a push rod at very small angles of the control lever so that the servo-piston 45 then assumes the " closed stop position regardless of the capsule 40.