Patent GB-620052-A (GB)
Title: Improvements in or relating to apparatus for metering the fuel supplied to a prime mover
IPC: G01F9/00
Filed: 1946-06-03
Abstract: 620,052. Fluid-pressure servomotor-control systems; valves. NAPIER & SON, Ltd., D., CHAMBERLIN, R. H. D., WYNNE, C. H. L., and SKELLERN, J. June 3,1946, No. 16828. [Class 135] [Also in Group XXVI] In a fuel metering device for a prime mover of the type in which a compressor delivers air to fuel combustion chambers and the products of combustion drive a turbine coupled to the compressor, the device comprises a metering orifice, the dimensions of which in two directions at right-angles are determined by two relatively movable members H<SP>1</SP>, F, a variable delivery pump B which delivers fuel to the metering orifice and is driven by the prime mover, means for moving the member F in accordance with the temperature of the air at the intake to, or at a point in, the compressor, a servomotor P for moving member H<SP>1</SP> and being controlled in accordance with the fuel pump (and prime mover) speed in association with the pump inlet pressure, a second servomotor T<SP>1</SP> controlled by air pressure at the intake of, or at a point in, the compressor and operating to vary a spring C<SP>5</SP>, loading a capsule C, subjected to the differential pressure across the metering orifice, and means by which the movement of this capsule determines the setting of the stroke of pump B. The latter is of the variable swash-plate type and delivers fuel which it receives from a tank A via a filter A<SP>2</SP> through a line D to the metering orifice, the outlet from the orifice being through a groove El, past a non-return valve E<SP>5</SP> and a manually-actuated shut-off valve W to a line E<SP>6</SP> leading to the combustion chambers. Fuel is also delivered by the pump to a chamber B<SP>13</SP> and, due to the centrifugal action of the pump, the pressure of this fuel is proportional to the speed of the prime mover. This pressure is applied to the upper side of a diaphragm B<SP>8</SP> and, through a line R<SP>5</SP>, to the inside of a capsule R<SP>2</SP>, and the pressure of the fuel at the inlet to the pump is applied to the underside of the diaphragm and to the outside of the capsule. The diaphragm actuates a hinged valve B' controlling a leak orifice leading from one side of a servomotor piston B<SP>4</SP>, the output pressure of the pump being applied to the other side of piston B'. The two sides of the piston are interconnected by a restricted passage, and the position taken up by the swash-plate of the pump, and hence the output of the pump, is thus determined by the speed of the prime mover in association with the pump inlet pressure. These two factors also determine the position of the ported sliding member H<SP>1</SP> of the metering orifice through the action of capsule R<SP>2</SP>. The latter actuates a piston valve R which controls servo-piston P, there being a repeat-back connection from the servo-piston through an eccentrically-pivoted lever Q on to a moving cylindrical seat Q<SP>3</SP> for the valve R. The second member F of the metering orifice is constituted by an unported cylinder sliding over member H<SP>1</SP>, and its position is controlled by a thermometer bulb situated at the intake &c. of the compressor, the thermometer bulb being connected to a Bourdon tube O which is connected to member F through the medium of an eccentrically pivoted lever O<SP>1</SP>. A cylinder E<SP>2</SP> constitutes a third member of the metering orifice, and whilst member E<SP>2</SP> normally occupies a fixed position, it may be adjustable. The pressures of the fuel on the inlet and outlet of the metering orifice are applied, respectively, to the inside and outside of capsule C, and the latter, through the agency of a lever K, actuates a hinged leak valve L<SP>2</SP> which acts in parallel with leak valve B<SP>7</SP> and so helps to control the stroke and the output of pump B. When the above system is applied to a prime mover for an aeroplane, the ram pressure, i.e. at the intake of the compressor, is applied to the outside of an evacuated capsule S which actuates a piston valve S<SP>6</SP> controlling servo-piston T<SP>1</SP>. The latter has a repeat-back connection with valve S<SP>6</SP>, through an eccentrically-pivoted lever V and a moving seat sleeve V<SP>3</SP>. A roller on servopiston T<SP>1</SP> engages in a cam slot in a lever N, and movement of the latter will' vary the rate of spring C‹ which constitutes a loading spring for capsule C. The port H in the member H<SP>1</SP> may be replaced by two separate ports produced by dividing the present port by a vertical medial line. Specifications 577,016 and 683,487 are referred to.