Patent GB-612711-A (GB)
Title: Improvements in or relating to control mechanism for internal combustion engines
IPC: F02D9/00
Filed: 1945-02-02
Abstract: 612,711. Fluid-pressure servomotor-control systems. BENDIX AVIATION CORPORATION. Feb. 2, 1945, No. 2692. Convention date, Jan. 10, 1944. [Class 135] [Also in Groups XXVI, XXVII and XXXV] In a control mechanism for aircraft engines in which a primary supercharger is arranged between the throttle and the intake manifold and an auxiliary supercharger is arranged in the carburetter inlet portion of the induction passage on the inlet side of the throttle, variable datum means controlled by a pilot's power lever automatically to maintain a predetermined relationship of intake manifold pressure and carburetter inlet pressure for each setting of the lever. The same lever may also control the engine speed by controlling the pitch of the propeller blades, a separate overriding hand-lever being provided to adjust the pitch governor when required. The speed or pitch control may be entirely separate from the pilot's power lever in which case the pressure rise across the primary supercharger is utilized to modify the boost produced by the auxiliary supercharger so that a desired manifold pressure may be maintained despite changes in engine speed. The latter arrangement may however be incorporated in mechanism where the speed or pitch control is through the pilot's power lever. As shown in Figs. 1 and 2, an engine-driven supercharger 16, which may be of the multi-speed or multi-stage type is arranged between the throttle 22 and the intake manifold 18. A second supercharger 27 of the turbo type is arranged in the induction pipe 10 between the air inlet 11 and the throttle 22. Fuel from a carburetter 19 such as that described in Specification 551,125, [Group XXVII], is discharged through a nozzle 21. The impeller 29 of the supercharger 27 is driven by a rotor 32 impelled by the exhaust gases in a pipe 33, the speed of the rotor being controlled by a waste gate 34 under the control of a motor 40. The latter is controlled by a switch comprising contacts 121, 122, 123, 124 of which the two first are carried by an arm 120 mounted on the free end of a rod 115 connected to a bellows 112 adjust - ably anchored in a chamber 113. The bellows is subject through a pipe 114 to the pressure in the carburetter inlet portion of the induction pipe 10. The motor 40 is subject to two overriding controls: (1) a governor-operated switch 137 which operates to prevent the supercharger 27 exceeding a maximum speed and (2) a pressure-operated switch 131 which operates to prevent the carburetter inlet pressure in the induction pipe 10 falling below a certain minimum above atmospheric pressure. The throttle 22 is actuated over a certain range by the pilot's power lever 58 and thereafter through a fluid-pressure servomotor by a variable datum boost control, as described in Specifications 572,647 and 573,691. In the present case, however, the internally-toothed member 48 which is connected by an arm 60 and a link 59 to the pilot's lever 58 has in addition to the cams 61 and 62 controlling respectively the pitch governor 24a and the datum spring 71 of the boost control, an additional cam 63 which through a lever 72 adjusts the stressing of a spring 118 which tends to keep the bellows 112 from collapsing. A further lever 146 is provided which through a lost motion connection 147a and a link 26 acts on the pitch control 24a to produce speeds in excess of that set by the cam 61 when required. Thus the hand lever 58 through the cams 61, 62, 63, respectively, controls in a predetermined relation the setting of the pitch governor 24a, the datum of the manifold pressure acting on the bellows 74 and the datum of the pressure in the carburetter inlet portion of the induction pipe acting on the bellows 112. Fig. 2 shows the arrangement of the various switches with equivalent but slightly different mechanical parts of the mechanism. The motor 40 comprises an armature shaft 39 driven in opposite directions by field coils 41, 42 selectively energized by relays R1, R2 which are themselves selectively energized by the closing of contacts 122, 124 and 121, 123 respectively. The shaft 39 carries an arm 38 which operates limit switches L<1>, L<2>. A battery B supplies current to the motor coils 41, 42 and to the relay coils the former being controlled by a rheostat. The minimum pressure switch 131 comprises a bellows 131a subject internally to the carburetter inlet pressure and externally to atmospheric pressure and the pressure of a spring 131c. The bellows carries a contact 128 movable between fixed contacts 129, 130. Normally the contacts 128, 130 are in engagement, but on disengagement due to the carburetter inlet pressure falling below a certain value above atmospheric pressure, the waste gate opening circuit through the contacts 121, 123 and the relay R2 is interrupted and control by the bellows 112 ceases to be effective. On a further fall in pressure, the contacts 127, 129 engage and the waste gate opening circuit is established through the relay R1, this circuit being broken when the carburetter inlet pressure again attains such a value as to break the contacts 128, 129. The governor-operated switch 137 similarly comprises a contact 139 movable between fixed contacts 140, 141. When the contacts 139, 141 are interrupted by the supercharger 27 exceeding its maximum speed, the waste gate closing circuit through contacts 122, 124 and the relay R1 is broken and further control by the bellows 112 is pre. vented. If the supercharger speed so much exceeds the maximum value that the contacts 139, 140 engage, the waste gate opening circuit is completed through the relay R2 and the speed of the supercharger is reduced to a safe value. Fig. 5 shows a modified arrangement in which the pitch governor 24a is regulated directly by a separate hand lever 160, the boost or intake manifold pressure and the carburetter inlet pressure as before being regulated by the bellows 74<1>, 112<1> respectively, and adjusted by a hand-lever 58<1> which through a link 59<1> and cams 62<1>, 63<1> acts on the datum springs 71<1>, 1181 of the respective bellows 74<1>, 1121. To compensate for changes in engine speed, the pressure rise across the engine-driven supercharger 16<1> is applied to the opposite sides of a diaphragm 153 which divides a housing 152 into two chambers 150, 151. The diaphragm 153 is connected to the rod 115<1> which controls the contacts 121<1>, 1221, 123<1> 1241. A decrease in the pressure rise across the supercharger 16 due to a fall in speed acts in the same way as a fall in induction pipe pressure on the rod 115<1>, i.e. under the loading spring 118<1> the contacts 122<1>, 124<1> are closed and the waste gate (not shown) is closed to speed up the turbo driven supercharger so that the intake manifold pressure may be kept at its set value. An increase in engine speed acts in a contrary sense. If the effective area of the diaphragm 153 is larger than that of the bellows 112<1>, automatic closing of the throttle will be necessary to increase the throttle loss and so maintain the intake manifold pressure constant. Similarly, the throttle must be opened automatically if the bellows 112<1> is larger than the diaphragm 153 to decrease the throttle loss caused by the change in pressure rise across the turbo driven supercharger. According to the Specification as open to inspection under Sect. 91, the bellows 112 may alternatively be subject to the pressure of the exhaust gases in the pipe 33. The Specification also shows a three-position switch, whereby the turbo-supercharger 27 may be switched over from automatic control to manual control, one of the two " manual " positions corresponding to the opening of the waste gate 34 and the other to its closing. This subjectmatter does not appear in the Specification as accepted.