Patent GB-572647-A (GB)
Title: Improvements in or relating to controls for internal combustion engines
IPC: F02D29/00
Filed: 1943-07-07
Abstract: 572,647. Fluid - pressure servomotor - control systems. BENDIX AVIATION CORPORATION. July 7, 1943, No. 11070. Convention date, April 27, 1942.. [Class 135] In a boost control system for an aeroplane engine, the control lever 42 is connected through a link 43 to a gear-wheel 32 of a sun-and-planet mechanism of which a pinion 31 carried by a lever 29, 30 is connected through a link 21 to the throttle 19, and gear-wheel 33 is actuated by a servomotor controlled by 'the enginecharging pressure. Variable datum means is operatively associated with the servomotor, and the datum is set by actuation of the control lever over, at least, a portion of the power regulating range. The position of the members as shown in the Figure corresponds to idling conditions under which the engine-charging pressure in conduit 64 is insufficient to collapse the evacuated bellows 60 against the action of its loading spring 57. The servomotor control valve 67 is then so positioned that pressure' fluid from a pump 80 can enter through port 75 and. flow out through port 74 and passage 83 to assist a spring 41 in keeping the servomotor pistons 35, 36 in the extreme left-hand position in which a rack 34 connecting the pistons virtually locks thewheel 33. As the lever 42 is advanced slightly towards a stop 95, wheel 32 rotates in an anti-clockwise direction and, by its engagement with pinion 31, lever 29, 30 is rotated to open the throttle slightly. During the movement of wheel 32, a roller carried by a bell-crank lever 50 starts to ride up a cam surface 47 on the wheel 32 so that fingers 53 on the lever 50 press on a collar 56 which puts further tension on the spring 57. As the engine-charging pressure is still not sufficient to collapse the bellows, the rod 55 which is connected to the bellows at one end, and is acted upon by the spring 57 at the other end, moves to the right and a pivoted lever 66, connected between the rod 55 and valve piston 67, moves the latter to the left to its neutral position where a land 69 is opposite the inlet groove 75 which it does not quite cover. The range of direct manual actuation of the throttle extends nearly up to cruising speed. Further movement of lever 42 will put further tension on spring 57 so that piston 67 is moved to the left to put passage 83 into communication with the interior of casing 27 through port 74, and to allow pressure fluid to flow from inlet 75 to port 76 and through passage 82 to act upon and press servomotor piston 35 and rack 34 to the right. This will rotate wheel 33 and, through pinion 31 and lever 29, 30, the throttle will be opened until the pressure transmitted through conduit 64 from the annular discharge ring 15 of a supercharger 14 is sufficient to collapse bellows 60, which action will move rod 55 to the left and valve piston 67 to the right to its neutral position. Changes in altitude will affect the charging pressure and by affecting the bellows 60 will correspondingly change the throttle opening.' When the throttle is near its wide open position, the servomotor can be tripped by a device comprising a spring- loaded stop 92 in line with the rod 55. When a projection 93 on lever 29, 30 contacts the stop 92, the latter will move rod 55 to the left and valve 67 will return to the right. Pressure fluid need not be supplied to chamber 38, in which case the spring 41 is relied upon to move rack 34 to the left. Wheel 32 carries a second cam surface 46 over which rides a roller carried by a pivoted lever 48, the latter being connected by a link 25 to a propeller pitch governor 23, the setting of which can thus be correlated with the position of lever 42 and the charging pressure. Hunting of the servomotor is prevented by spring-loaded rods 104, 105, the ends of which normally press against a rod 106 carried by the valve piston 67. To allow a rapid initial response of the valve to a quick movement of lever 42, the end of lever 52 is connected to a rod joining further pistons 100, 101. A sudden movement of lever 52 to (say) the right will cause piston 100 to withdraw fluid from the back of piston 102 and the latter will be withdrawn out of contact with rod 106 to allow the latter to make an initial movement. Piston 102 will be returned by its spring as fluid is drawn in through a restricted aperture 108. The compressing movement of piston 101 will force fluid out through the corresponding restricted aperture or through a non-return valve 112. Stop 95 limits the normal stroke of lever 42, but the stop is spring loaded and a slight further movement of the lever can be obtained by pressing it down on to the stop. Ports 39, 40 in the pistons 35, 36 ensure circulation of the fluid to prevent freezing. Fuel is fed to the engine through a carburetter 16 ; the supercharger may be positioned before the carburetter, or two superchargers which may be of the single or multi-speed types may be employed. The fluid-pressure servomotor may be replaced by an electric servomotor. Specification 523,895, [Group XXVII], is referred to.