Patent GB-597396-A (GB)
Title: An improved means for controlling the operation of aircraft engines
IPC: F02D9/00
Filed: 1944-08-17
Abstract: 597,396. Fluid-pressure servomotor-control systems. GENERAL MOTORS CORPORATION. Aug. 17, 1944, No. 15776. Convention date, Aug. 17, 1943. [Class 135] In a control device for the engines of aircraft, such as disclosed in Specification 594,074, in which a single main control lever is operated by the pilot to select the intake manifold pressure and also to adjust the setting of the propeller governor in accordance with a predetermined schedule of pressure and speed, means are provided whereby the normal schedule corresponding to the various positions of the control lever may be modified for conditions such as excess load without charging the setting of that lever. Means are also provided to effect a return automatically to the normal schedule should the main control lever be moved into certain positions such as " idling " or " emergency power." In Fig. 23, a hand lever 210 in the pilot's cockpit operates the main control lever 125 and shaft 20 of the control device, which shaft rotates an arm 18, Fig. 11, which carries a cranked lever 14, 28, one end 14 of which is connected by rod 12 and link 11 to the throttle valve V of the engine while the other end 28 is connected by link 30 to the piston-rod 32 of a servomotor. From the idling position of the throttle V of about 10 degrees open to approximately 50 degrees open, the servomotor does not function and the control is entirely manual, the lever 14, 28 thus pivoting about the fixed end 31 of the rod 32 to operate the valve V. The shaft 20 also carries internally of the device a cam member 141, Fig. 1, with a suitably shaped cam track 142 which acts through levers 145, 150 to adjust the setting of a propeller governor 152, Fig. 23, in accordance with the desired relation between the intake pressure and the propeller or engine speed. The shaft 20 also carries an arm 124, Fig. 11, which is connected through links 120, 117 to a shaft 110 which carries a cam 105, Fig. 5, acting on one end of a lever 83, the other end of which is connected to a valve 66 controlling a piston 34 of the servomotor. This cam 105 is so shaped that it is effective to bring the servomotor into operation only after the desired manual range of operation of valve V is passed in which the piston 34. is held to the right by the pressure fluid and a spring 38. The centre of lever 83 is pivoted on a pin 84 carried between two bellows members 88, 89, the first 88 being evacuated and enclosing springs 101, 102 so as to respond to changes of altitude and the second being connected to the engine intake manifold or supercharger scroll so as to respond to the selected intake pressure. Thus, in the automatic range from 50 degrees open to full open position of the valve V, the pressure is regulated by bellows 89 to the value selected by the control lever operated cam 105, but compensated for changes in altitude by barometric pressure acting on bellows 88. To enable a change to be effected from the normal power schedule in relation to the main control lever positions, a " modifier " lever 220, Fig. 23, is provided in the cockpit which is connected by a flexible cable 221 to a lever 114 of the control device. The lever 114 can be moved from a normal position shown in Fig. 1 to a position engaging a stop 223 which allows the movement of a second lever 112 under a spring 224. This lever 112 has a base 111 in which the shaft 110 of cam 105 is eccentrically mounted so that movement of modifier lever 220 from a position corresponding to zero excess load to a position corresponding to 3000 lbs. excess load effects a corresponding adjustment of cam 105 and thus a corresponding change in the power schedule without affecting the main control lever position. Should the main control lever 125 be returned to the idling position before the " modifier " lever is returned to normal, a cam 231 on the lever 117 secured to shaft 110 engages a fixed roller 233 to move the lever 112 back to its normal position as shown in Fig. 1 against the spring 224, the lever 114 subsequently also being returned to normal position by the return of a mixture lever 250, Fig. 23, to an idling position and engaging lever 220 through a pin-and-slot connection. The lever 112 is also returned to normal in the event of the main control lever being moved to "emergency" or full power position, the lever 117 in this event engaging a stop screw 230 on an extension of the lever 112. The casing of the control device is normally filled with oil which provides for damping the action of the bellows 88, 89 and a thermostatic valve 193, Fig. 1, is provided for byepassing cold oil around the control valve 66 until the engine has " warmed up."