BYPASS VALVE WITH CONSTANT FORCE-VERSUS-POSITION ACTUATOR

摘要

A control arrangement for a fuel system having a fuel pump (13) for supplying fuel through a variable orifice flow metering valve (15) to an engine main fuel control (45), the control (45) controlling the fuel pressure differential across the orifice of the metering valve (15). A head sensor includes a movable diaphragm (51), a bypass valve (47) for diverting fuel from the fuel pump away from the metering valve (15), and a coupling between the diaphragm (51) and the bypass valve (47) whereby the bypass valve (47) opens and closes in response to diaphragm (51) motion. The metering valve orifice fuel pressure differential is applied across the diaphragm (51) so that a valve spool (55) may open and close to maintain the pressure differential across the metering valve (15) substantially constant. A bias spring (54) normally biases the spool (55) closed. An electrically variable bias force may be applied to the diaphragm (51) to selectively increase or decrease the normally maintained pressure differential across the metering valve (15) and, therefore, also selectively increase or decrease the fuel flow to the engine. The electrically variable bias force is applied by a linear actuator (50, 80) which includes a helical actuating coil (61, 77), a rod (63; 79a, b, c) extending through the helical coil (61, 77) and a permanent magnet (59; 73, 75) fixed to the rod (63; 79a, b, c) and spaced axially from the coil (61, 77). When an energizing current is supplied to the coil (61, 77), force is applied to the magnet (59; 73, 75) which is generally proportional to the distance between the coil (61, 77) and the magnet (59; 73, 75). A second force is also applied to the rod (63; 79a, b, c) and is generally proportional to rod position. The resultant of the two forces is substantially independent of the spacing between the coil (61, 77) and the permanent magnet (59; 73, 75). When two magnets (73, 75) are used, the sum of the two distances from the coil (77) to the magnets (73, 75) is maintained constant.