Patent GB-631752-A (GB)
Title: Improved boost control mechanism for supercharged internal combustion engines
IPC: F02D9/00
Filed: 1947-03-27
Abstract: 631,752. Fluid-pressure servomotor control systems. GENERAL MOTORS CORPORATION. March 27, 1947, No. 8286. Convention date, May 4, 1946. [Class 135] In a boost control mechanism for a supercharged internal combustion engine, for use in aircraft, the manually-operable cam for selecting a desired, automatically maintained engine intake pressure is rotatable about an offset pivot additionally to its normal rotational selective movement so that it is effective for a normal or a modified series of pressure selections. Actuation of the pilot's control rotates a shaft 36, Fig. 8, and this movement is communicated to the throttle to open the latter through a lever 57, floating lever 51, link 49, lever 44 and shaft 41. Screw stops 58 limit the range of movement of lever 57 and a further screw stop 46 prevents the throttle from moving past the full open position. The movement given by the pilot to shaft 36 also selects a datum boost pressure, this movement causing a servopiston 61 to act on floating lever 51 and so open the throttle by an amount additional to the direct manual actuating movement. The boost pressure selected is maintained by means of interconnected bellows 101, 111, Fig. 7, the former being evacuated and the latter subject internally to engine intake pressure, and the bellows, through a floating lever 97, actuate a valve 92 which controls the connection of pressure fluid or exhaust to the servo-piston 61. Bellows 111 is loaded by an internal spring, and bellows 101 is loaded internally by two springs and is carried by a screw means 105 by which it can be adjusted initially in position. As the throttle reaches wide open position, arm 44 engages a lug 150 on a lever 148 which is swung round to engage and re-centre valve 93 so that the servo-piston becomes hydraulically locked and there is no tendency to move the throttle past wide open position. The pressure selection device comprises a cam 130 pivoted to an arm 132 carried by shaft 36 and acting on a cam follower roller 136 carried by one arm of a three-armed lever 138 of which a second arm 144 is connected by a link 145 to the floating lever 97. Cam 130 is normally spring- held against an abutment 133 on arm 132, but it can be swung outwards by a roller 160 to an alternative position in which a fresh series of pressure relationships is obtained. Roller 160 is eccentrically mounted on a shaft which can be actuated manually or through a servomotor when the gear drive to the blower is changed. When the blower is shifted into high gear, a valve is opened and pressure liquid flows to and lifts a valve 193, Fig. 17, to shut off the flow of pressure liquid through a pipe 191 to the servomotor and, at the same time, connects the servomotor to exhaust through passages 201 and 204. The resultant movement of the servomotor swings cam 130 to its alternative position. In normal operation, the highest pressures selected cannot be obtained due to an abutment 210, Fig. 24, which prevents the roller 136 from following the cam 130. Abutment 210 is carried on a lever 212 and the latter is swung away to allow the roller to follow the cam and so give the upper range of pressure selections when a diaphragm connected by links and levers to lever 212 is subject on one side to the pressure of an anti-detonant liquid injected into the engine. The diaphragm is subjected on its other side to ram pressure. An abutment 189 carried by a lever in the chain connecting the blower gear shift servomotor with the roller 160 also acts on lever 212. Specifications 597,396 and 600,963 are referred to.