Patent GB-1452979-A (GB)
Title: Carburetor having an engine idle speed control
IPC: F02D9/02
Filed: 1974-12-20
Abstract: 1452979 Extra fuel for starting FORD MOTOR CO Ltd 20 Dec 1974 [4 Jan 1974] 55301/74 Heading F1H A carburetter has a fuel enrichment system for cold starting and a fast idle cam which prevents the throttle valve closing to the normal idling position, the fast idle cam having two axially-separated stepped cam surfaces each of the steps of one cam being at a greater distance radially from the cam centre than the corresponding step of the other cam and the cam being axially movable by means responsive to the intake manifold vacuum, so that the cam is moved axially during engine cranking to bring the larger of the cams into a position with a stop means which determines the extent to which the throttle closes. The carburetter has twin barrels 10, the cross-sectional area of the Venturi in each barrel being variable by movement of a wall 12, which carries with it a fuel control needle valve 16 which co-operates with a jet 18, to which fuel is supplied from a float chamber 20. Movement of wall 12 is controlled by vacuum-operated diaphragm 32, biased by spring 39 in vacuum chamber 30 to move wall 12 towards jet 18. Chamber 30 communicates via passages 41, 42 and 44 with chamber 48, Fig. 4, which opens through port 50 into the intake passage. There is a restrictor 46 at the entrance to chamber 48. A passage 52 branches off passage 42 and through passages 54 56, 58, 60 and opening 63, Fig. 6, communicates with wall 62 which is connected with the Venturi at a point just downstream of the throat. Opening 63 is controlled by a tapered pin 72, which is moved axially, by a link 174 and a temperature responsive member. The vacuum in chamber 30 is therefore equal to the vacuum at the port 50 as modified by the vacuum in the Venturi, to an extent controlled by the pin 72. Additional fuel during cranking. At the bottom of the float chamber is a spring-opened valve 100, Fig. 6, the degree of opening being controlled by block 144, mounted on needle valve 140, the position of which is determined through lever 166 by the link 174 and the temperature responsive member. Fuel flows through passage 112 to barrels 10 only when a solenoid valve (122) Fig. 7 (not shown) is energized by turning the ignition key to the "start" position. Additional fuel immediately after starting. When the engine is running, the solenoid valve closes and fuel flows through orifice 150 and passages 154 and 156 to barrels 10 to provide the rich mixture necessary for a cold engine. The amount of fuel is determined by the position of tapered needle valve 140. At the same time, tapered pin 72 is blocking opening 63 so that the full vacuum at port 50 acts on diaphragm 32, retracts the walls 12 and withdraws needle valves 16 to provide an enriched mixture. Temperature responsive member. Figs. 10 and 12. Link 174 is pivotally connected to lever 216 fixed on spindle 218 which is free to turn in sleeve 220 and has an enlarged end 226. Lever 228 is also fixed on spindle 218 and has a leg 232 which is slotted to receive the outer end of bi-metal spring 322. The inner end of the spring is secured in spindle 326 which can be rotated to adjust the preload on the spring and is locked by a clamping plate 330 and screws. A second leg 230 of lever 228 engages between lugs 234 and 235 formed on a fast idle cam 236 which is rotatable on, but axially fixed relative to a second sleeve 238 which is slidably mounted on sleeve 220. The weight of ball 246 biases the cam to rotate anti-clockwise. Fast idle cam surfaces 250 and 252 are provided, each surface consisting of four steps at increasing radial distances from the cam centre and each of the steps of surface 252 being at a greater radius than the corresponding step of surface 250. A plunger 254 engages the fast idle cam and its end 262 engages a lever 264 carrying an adjustable screw 268 which determines the extent to which the throttle valves can close. The second sleeve 238 and cam 236 are moved axially by pivoted lever (288) which is actuated by vacuum motor 300. Before the engine is started, spring 316 moves lever (288) to dotted line position 318 and brings larger radius cam surface 252 into alignment with plunger 254. If the temperature of spring 322 is very low, the spring will turn the cam to bring the greatest radius step of the cam under plunger 254 when the mechanism is set by opening the throttle valves wide and then releasing them. When the engine starts, intake manifold vacuum, which is communicated to chamber 310 is sufficient to overcome spring and move the fast idle cam to bring surface 250 of lesser radius under plunger 254. While the engine is running air is drawn through an exhaust gas heated stove, through pipe 336 and over spring 322 so that the fast idle cam turns to bring steps of decreasing radius under plunger 254.