GB1446514A - Carburettor automatic choke system - Google Patents

Abstract

1446514 Automatic choke valves FORD MOTOR CO Ltd 29 July 1974 [6 Aug 1973] 33365/74 Heading F1B An automatic choke system for use with a carburetter having an air/fuel induction passage and an unbalance mounted choke valve comprises a first temperature responsive spring means which urges the choke valve towards the closed position with a force which increases as the temperature of the spring decreases from a first predetermined temperature, power means adapted to be connected to engine manifold vacuum to move the choke valve towards an open position in opposition to the action of the first spring means and second temperature responsive spring means connected to the power means for controlling the effect of the power means on the choke valve as a function of the temperature changes of the second means from a second predetermined level. Choke valve 28 is mounted on a spindle 30 and at one end has a lever arm connected by link 52 to arm 48 on shaft 44 which carries arm 58 attached to the outer end of coiled bi-metal strip 60. When cold, strip 60 turns choke valve 28 to its closed position. Hot gas is drawn through housing 42 by manifold vacuum to heat strip 60 and turn choke valve 28 towards its open position. At the other end of spindle 30 is fixed a second lever 90 which is engaged by pin 92 carried by one arm 94 of bellcrank 96, fixed on shaft 98 which is mounted in bearings 100 in bracket 102. A second coiled bi-metal strip 122 has its inner coil fixed to the other end of shaft 98. Freely mounted on shaft 98 is a yoke 112 which carries a screw 108 which can engage the other arm 106 of bell-crank 96. Yoke 112 also carries a pin 114, which passes through the eye of a pull rod 118 and is attached to the outer end of coiled strip 122. Pull rod 118 is attached to diaphragm 128 of a vacuum operated motor. One side of diaphragm 128 is open to atmosphere through a restricted orifice 140 and a check-valve 144. Tension spring 134 connects the first diaphragm to a second diaphragm 130, one side of which is connected by passages 152, 154, 156 to the intake manifold, downstream of throttle valve 26. Operation. In cold weather, strip 60 shuts choke valve. Screw 108 is adjusted to separate lever 96 from finger 110 to unwind spring 122 by an amount sufficient to provide an initial load opposing movement of pull rod 118 so that manifold vacuum during engine cranking will not move diaphragm 130 against the force of coiled strip 60. As soon as the engine starts, the increased manifold vacuum will be sufficient to move diaphragm 130 downwardly (to the position shown in Fig. 4) and through spring 134 will pull diaphragm 128 downwardly at a rate determined by the passage of air through orifices 149 and 148, thus opening the choke valve by a small amount e.g. 6 degrees. As the engine temperature increases, the force exerted by coiled strip 60 decreases and allows the choke valve to open. When the ambient temperature is above a predetermined level, coiled strip 122 will rotate lever 106 to open the choke valve in accordance with the ambient temperature.