GB1422955A - Carburetters for internal combustion engines - Google Patents

Abstract

1422955 Spray carburetters BRITISH LEYLAND UK Ltd 1 Nov 1973 [4 Nov 1972] 50912/72 Heading F1B Constant depression carburetter includes a vapour duct 4 connected to the float chamber air space, an outlet duct C connected to the constant depression region of the carburetter, and air duct D connected to a supply of air, each of the above ducts being connected to a flow control means F which includes a flow regulator to simultaneously regulate flows along the vapour and air ducts 4 and D to the outlet duct C so that the ratio of flows into duct C is maintained constant regardless of flow-rate, and a pressure sensitive element in communication with the vapour duct to adjust the flow regulator to increase flow along the vapour and air ducts with increasing pressure in the vapour duct and vice versa. The flow control means comprises housing 3 divided by diaphragm 1 into chamber 2 which is open to vapour duct 4 and chamber 17 which is open to air duct D. A second diaphragm 14 defines a third chamber 15 which communicates with chamber 17 through the bore of a tube 16 and port 20. The upper end of tube 16 is formed as a valve seating for diaphragm 1. Valve member 18a co-operates with seat 19 in tube 16 and has a stem 18 which engages diaphragm 1. Pivotally mounted on the housing is a plate valve 10 which co-operates with a valve seat 8 and a second valve seat 9. The circumference of valve seat 9 is five times that of valve seat 8, and the lift of the plate 10 on seat 9 is five times the lift on seat 8, so that the effective valve openings are in the ratio 25:1 Vapour pressure in conduit 4 moves diaphragm 1 and displaces valve member 18a and allows vapour past valve seat 8 and air past valve seat 9 to form a 12¢:1 mixture in chamber 13. As the vapour pressure in duct 4 decreases, diaphragm I rises, and atmospheric air passes seating 22 and enters chamber 15. An auxiliary valve 100 vents duct 4 to duct D when the engine is stopped. Spring 24 biases diaphragm 23 to open valve 100. To compensate for changes in atmospheric density a series orifice arrangement is provided, Fig. 4, in which duct 29 is connected to chamber 17, orifice 27 leads to duct C and the upper part of the device is connected to atmosphere and to duct D, chamber 17 being isolated from duct D. An aneroid capsule 30 controls the position of a valve 31 which determines the effective size of the orifice 26. The capsule may contain a dry inert gas so that it is responsive to a change in air temperature as well as pressure. The series orifice arrangement can result in cancellation of the enrichment for acceleration normally provided by the hydraulic piston damper, in a modification this effect is avoided by a further valve which admits atmospheric pressure to the float chamber, Fig. 5 (not shown).