Patent GB-1458191-A (GB)
Title: Mechanical linkage
IPC: G05G11/00
Filed: 1973-05-03
Abstract: 1458191 Linkwork LUCAS INDUSTRIES Ltd 28 March 1974 [3 May 1973] 21025/73 Heading F2K [Also in Division B7] In a linkage having 1st and 2nd input levers 14, 25 and an output lever 16, all pivotally mounted on a carrier 12 which is itself pivotally mounted at 11 to a fixed support 10 with the carrier pivot 11 and 2nd input lever pivot 24 axially aligned, the output lever 16 is angularly movable about the same axis as the 1st input lever 14 and is operable alternatively by the input levers 14, 25 through an arrangement of six equal-length links 15, 17-20 and 23 such that in one position of the linkage, as determined by the position of the 1st input lever 14 relative the carrier 12, movement of the 2nd input lever 25 has no effect on the output lever 16 and the output lever 16 is moved by the 1st input lever 14 alone, while for other positions of the linkage as determined by other positions of the 1st input lever 14 relative the carrier 12, movement of the 2nd input lever 25 moves the output lever 16 by an amount dependent on the position of the linkage. As shown, the 1st input lever 14 is releasably connected by latch projections 26 to the carrier 12 such that when latched thereto to jointly pivot with the carrier 12 about fulcrum 11, the interconnecting arrangement of links 15, 17-20 and 23 are positioned so that a common pivot 21 of links 18-20 is aligned with the carrier pivot 11 and pivot 24 of the 2nd input lever 25 whereby movement of the 2nd input lever 25 has no movement effect on the position of the output lever 16. When the 1st input lever 14 is released i.e. unlatched from the carrier 12 and relatively angularly adjusted thereto, the common pivot 21 of the links 18-20 is moved offset from the aligned axis of the carrier pivot 11 and 2nd input lever 24 whereby movement of the 2nd input lever 25 moves the output lever 16 by an amount dependent on the position of the 1st input lever 14. The linkage may be included in an engine fuel control system of a helicopter, the output lever 16 being coupled via a control arm 31 to a variable metering device 30 for controlling fuel flow from a pump to an engine 35, the 1st input lever 14 forming an engine power selector lever and the 2nd input lever 25 being coupled to a collective pitch selection lever 32 for the helicopter blades whereby in normal operating conditions, changes in fuel flow in response to changes in collective pitch are effected by an electronic control device 34, the control arm 31 operating a volume control whereby the response of the metering device 30 to the control device 34 can be varied. In normal operating conditions, the 1st input lever 14 is latched to the carrier 12 so that movement of the 2nd input lever 25 by the pitch selector lever 32 has no effect on the position of the output lever 16 which, in this condition is moved by the 1st input lever 14 alone. In the event of failure of the electronic control device 34 the 1st input lever 14 is unlatched from the carrier 12 and moved clockwise to a maximum engine power position, which position also allows control of the engine fuel flow metering device 30 by the 2nd input lever 25 via the collective pitch selection lever 32.