GB742576A - A new or improved system and means for controlling the speed of internal combustion engines and turbines - Google Patents

Abstract

742,576. Fluid-pressure servomotor control systems. PLESSEY CO., Ltd. March 4, 1953 [Jan. 22, 1952], No. 2060/52. Class 135. A speed-governing system controlling the liquid fuel supply to an internal-combustion engine or a gas turbine in two stages, viz., by controlling the size of a metering orifice and the pressure drop across it, includes a centrifugally-loaded control valve driven by the engine and so proportioned as to be unaffected by variations in the density of liquid in which it rotates. As shown in Fig. 1, fuel is fed from a pump 2 to a metering orifice 4 whence it passes to a delivery conduit 5, and the pressure drop across the metering orifice is controlled by a by-pass valve 7 actuated by a servo-piston 20 controlled by a valve 17. This valve is actuated jointly by a diaphragm 23 which exerts a downward force as a function of the speed of the engine and by a diaphragm 24 which also exerts a downward force proportional to the pressure drop across the metering orifice, a spring 30 balancing these two forces. The force which is a function of speed is provided by pressure of fuel in a conduit 25 which is connected through a restriction 9 with the main fuel conduit 3 and has a tapping 10 leading to a, valve 11 having a weight 98 and rotated at engine speed whereby the pressure in the conduit 25 is limited to that required to open the valve 11. The valve 11 is unaffected by variations of density of the fuel. The lower side of the diaphragm 23 is connected by a conduit 26 to low pressure at the outlet from the valve 11. An adjustable valve 37 controls leakage through restrictions 33, 34 from the conduit 25 to vary the datum of the apparatus. The arrangement is such that when, e.g., the speed of the engine increases the valve 17 is urged downwardly, thereby reducing the inflow of fuel to the chamber at the lower side of the servo-piston 20 and causing the latter to open the by-pass valve 7. This will result in a lower fuel flow through the metering orifice and, therefore, a lower pressure drop across it. The pressure upstream of the orifice 4 is conveyed through a hollow stem to the left-hand sida of a piston 43 whilst that at the downstream side is transmitted by a conduit 28 and a restriction 44 to the right-hand side of the piston 43 upon which also acts a spring 46. A part 41 of the piston 43 acts as a valve controlling the inflow of fuel to a chamber to the left-hand side of a servopiston 40 which is spring urged to the left and actuates a tubular member which controls the size of the metering orifice. Thus, in response to a reduction of pressure drop across the metering orifice the servo-piston 40 is caused to move to the left to reduce the effective size of the metering orifice to restore the original pressure drop. The right-hand sides of the two pistons 40, 43 are subject to a common pressure. In the form shown in Fig. 2 the pressure which is a function of engine speed is applied through a conduit 83 to the space between a pair of diaphragms 82, 84 which actuate a valve 70 controlling the servo-piston 69 of a by-pass valve as in the previous example. The other side of the diaphragm 84 is subject to the pressure upstream of the metering orifice 61 conveyed through a conduit 85 and the other side of the diaphragm 82 is connected through a restriction 90 to the point downstream and also to a chamber between the servo-piston 73 which actuates a plunger 72 for varying the area of the metering orifice and a diaphragm 79 which operates a valve 75 controlling the pressure applied to the left-hand' side of the servo-piston 73. A loading spring 78 for the valve 75 is adjustable by a cam 88 to vary the governed speed.