| 摘要 |
1,237,680. Gas turbine engine fuel systems. BENDIX CORP. Dec. 12, 1969 [Dec. 20, 1968], No. 60755/69. Heading F1G. A gas turbine engine fuel system comprises a by-pass valve 78 for maintaining a constant pressure drop across the fuel metering valve 72, and a dashpot connecting the by-pass valve to the operating spindle 58 of the metering valve to temporarily restrict movement of the by-pass valve in response to its actuating piston 80 whereby when the metering valve moves in response to a variation in a control signal, the by-pass valve initially moves in unison with it and the actuating piston subsequently resumes control of the by-pass valve. The dashpot comprises a piston 90 co-operating with chambers 92, 94, interchange of fuel between the chambers taking place through restrictors 96, 98 communicating via a duct 100 and a line 30 with the low-pressure side of the fuel pump 24. The metering valve 72 is actuated by a piston 102 subjected to a variable pressure difference between its opposite faces produced by the flow through a restrictor 114 controlled by a variable leak-off valve 116 carried by a beam 118 pivotally connected to a manual control 32 and to a senser 36 which senses an engine operating condition dependent on fuel flow, such as engine speed or an engine-generated temperature or pressure. If the metering valve 72 is being carried in, say, an upward direction to decrease the fuel flow, the by-pass valve 78 is initially carried upwards with it by virtue of the dashpot action, thereby increasing the by-pass flow to reinforce the action of the metering valve in reducing the fuel flow to the engine. The decrease in the pressure drop across the metering valve 72 caused by the opening movement of the by-pass valve 78 is greater than the increase caused by the closing movement of the metering valve, the net decrease allowing a spring 74 to move the metering valve relative to the spindle 58 to reduce the opening of a leak-off valve 68 which controls the flow through a restrictor 82. The resultant increase in the pressure above the piston 80 allows the piston to gradually overcome the resistance of the dashpot and move the by-pass valve 78 in a closing direction, thereby increasing the pressure drop across the metering valve 72. This increases the opening of the leak-off valve 68, which in turn decreases the pressure above the piston 80. This, in conjunction with the negative feedback to the beam 118 produced by the response of the sensor 36 to the reduction of fuel flow, stabilizes the system at the required fuel flow rate. |
