Patent GB-573496-A (GB)
Title: Improvements in or relating to apparatus for the control of internal combustion engines
IPC: F02D9/00
Filed: 1941-10-13
Abstract: 573,496. Fluid - pressure servomotor - control systems. NAPIER & SON, Ltd., D., HALFORD, F. B., and WALLACE, P. J. Oct. 13, 1941, No. 13144. [Class 135] A servomotor-control system for internal combustion engines used in aircraft is controlled by a capsule subject to boost .pressure and a single main pilotoperated control lever arranged to effect relative adjustment of the accelerator pump of the carburetter, the engine throttle, the ignition timing, the datum control of the boost servomotor, the setting of the carburetter for weak mixture and the setting of the airscrew governor so as to ensure the best engine performance at all times and minimize risk of mishandling the engine. The system includes the following characteristics : (1) The datum control of the boost servomotor is effected by adjusting the seat of the boost servomotor-control valve so permitting practically the whole travel of the piston of the boost servomotor to be used for increasing the opening of the throttle with increasing altitude beyond the opening given to it by the hand lever. (2) The mechanism is provided with an " overrun " mechanism which allows the boost servomotor to open the throttle fully irrespective of the manual opening associated with the datum boost. The throttle, however does not pass beyond the position where it is parallel to the axis of the, venturi passage in which the throttle is placed. (3) The mechanism is arranged so that slow movement of the hand lever causes weak mixture and advances ignition to operate over a predetermined speed range while a rapid movement, as when accelerating for the takeoff, normal rich mixture is maintained. (4) At high altitudes weak mixture is automatically brought into operation. (5) To prevent hunting, there is a sufficient difference between the altitude, detected by the fall of boost pressure, at which high and low gears are engaged respectively while climbing and while descending. This is effected by correlating the fall of boost pressure with throttle valve opening. (6) Overriding manual control of the automatic gear change of the supercharger drive at high altitudes is only permitted when weak fuel mixture is being used above the altitude at which this override becomes operative. The pilot cannot pass from high gear in the supercharger drive at the higher boost pressures to economical cruising in low gear without first passing through the conditions of economical cruising in high gear. In this way the possibility of there being a disconcerting fall of engine power is avoided. (7) The change to high gear is prevented when the engine speed is above a predetermined speed selected by the hand lever, while the automatic change down to low gear remains unaffected and operates at all engine speeds. (8) The mechanism includes a number of " cam-gearing transmission " assemblies as described in Specification 551,760, [Group XXIV], arranged between rotating elements so that the nature of the movement transmitted can be arranged as desired. (9) All the principal parts are grouped in a single casing, the only parts external to the casing comprising the connections to the throttle valve, to the accelerator pump, the weak mixture lever on the carburetter, to the ignition unit servo, to the airscrew governor, and to the change-speed lever of the supercharger gear. The hand or pick-up lever D is mounted on a shaft D' carrying an arm E connected to the accelerator pump of the carburetter and connected by " cam-gearing " assemblies H<1> ... <6> and differentials J, K with an arm F connected to the throttle, with an arm G connected to the ignition timing mechanism, with an arm 20 connected to the air-screw governor and with the datum boost control. A member D<2>a mounted on a sleeve keyed to the shaft D <1> carries a pivot pin H'c for a two-armed lever, one arm of which carries a pin H<1>e movable in a cam slot H<1>f in a fixed member H<1>g, while the other arm carries a toothed sector H<1>d engaging a pinion K<1>. The pinion K<1> is mounted on a sleeve K<2> carrying at the other end a bevel sun-wheel K<3> coupled by planetary pinion K<6> with a bevel sun-wheel K<4> on a sleeve G<1> carrying the ignition control arm G. The member D<2>a also carries a pivot H<2>c for a two-armed lever, one arm of which carries a pin H<2>e movable in a cam-slot H<2>f in the member H<2>g, while the other arm carries a toothed sector H<2>d engaging a toothed sector J<1>. This sector is mounted on a sleeve J<2> formed with a sun bevel wheel J<3> coupled by planetary pinions J<6> with a sun bevel wheel J<4> mounted on a sleeve, on the other end of which is a two-part member J<5>, J<5>a which bridges the differential K and is supported in a bearing beyond the bevel wheel K<4>. The planet carrier J' for the differential J carries a member provided with skew teeth J<8>, and with a pivot H<3>c for a two-armed lever, one arm of which has a pin H<3>e movable in a cam-slot H<3>f in a member H<3>g, while the other end has a toothed sector H3d. The member H<3>g is suspended from an eccentrically mounted pivot 30 adapted to be rotated by helical splines R<2> on a hollow shaft movable longitudinally by a piston R<1> (Fig. 1), and is guided by a slot 31 engaging a rotatablymounted block 32. The carrier K<5> for the planetary pinions K<6> is rotatably mounted on the shaft D<1> and is formed with teeth engaging the toothed sector H<3>d. The bridging member J<5>, J<5>a carries the pivot H<4>c of a two-armed lever having a pin H<4>e engaging a cam-slot H<4>f in a fixed member H<4>g and a toothed sector H<4>d engaging a toothed sector F<2> on a sleeve F<1> carrying the throttle control arm F. The member D<2>a engages a toothed sector D<4> on a sleeve D<5> turning on a fixed part and carrying a further toothed sector D<6> engaging a toothed sector H<5>a mounted on a sleeve H<5>b. This sleeve carries the support H<6>a for the pivot H<6>c of a two-armed lever provided with a pin movable in a cam-slot and a toothed sector engaging a pinion 21 on a shaft carrying the arm 20 for controlling the air-screw governor. The member H<5>a carries the pivot pin H<5>c of a two-armed lever having a pin H<5>e engaging a cam-slot H<5>f in a fixed plate H<5>g and a toothed sector engaging a pinion L<4> formed integrally with a nut L<3> engaging a thread L<2> formed on one end of the ported tubular seat for the control valve B for the boost servomotor. This valve is actuated against the action of a spring B<1> by a capsule A anchored to a fixed part and subject to manifold pressure. The capsule and valve are coupled by a pair of racks engaging toothed sectors forming an idler. The piston C<1> of the power cylinder controlled by the valve B is loaded by a spring C<3> housed in a hollow piston-rod having a splined connection with a fixed part to prevent rotation. The rod is formed externally with a quick-pitched thread C<5> engaging the skew teeth on the planet carrier of the differential J. The piston-rod also carries an annular flange C<6> adapted when the piston-rod has moved a predetermined distance to engage an abutment L<9> on a member L<5> slidably mounted on a guide and provided with a fork engaging the nut L<3>. After this engagement the control valve seat is moved in step with the piston C<1> to give a follow-action. The change-speed gear P<1> of the supercharger drive is controlled hydraulically by a valve P actuated by a servomotor O. The weak mixture necessary for economical cruising is brought into operation over the appropriate speed range of engine speed by means of a small servomotor R, the piston-rod of which has splines R<4> engaging an arm Q coupled to the mixture control in the carburetter. Both of these servomotors are controlled by a pair of concentric and cooperating rotary valves M, N and by a valve T. The inner valve N has a tubular spindle provided with skew teeth N<2> engaging skew teeth L<13> on a shaft L<12> having a second set of skew teeth L<11> engaging skew teeth on the outside of the nut L<3>. The outer valve M has an extension formed with skew teeth M<1> engaging skew teeth C<7> on a shaft C<8> having a second set of skew teeth engaging a quick-pitched screw C on the piston-rod C<2> of the boost servomotor C. The arrangement of ports in the valves M, N is described in detail in Specification 552,679. The valve T is actuated by a toothed pinion engaging the toothed member H <5>c actuated by the hand lever D. The valves M, N and T act through relay valves S, U, V. To enable the pilot to override the automatic gear change in order to effect economical cruising at high altitude when the servomotor R is in the weak fuel mixture position, a hand-actuated valve W is provided.