GB1475008A - Carburetor cranking fuel system - Google Patents

Abstract

1475008 Supplying extra fuel for starting; temperature responsive control FORD MOTOR CO Ltd 20 Dec 1974 [4 Jan 1974] 55304/74 Heading F1H A carburetter for an I.C. engine and having an engine cranking fuel supply system comprises an induction passage 10 for connection between a source of fresh air and an I.C. engine intake manifold, a fuel port opening into the passage a fuel passage 112, 114, (116), 124, 126, 128, Figs. 5, 6 7 and Fig. 8 (not shown) connected at one end to the fuel port and at its other end to a fuel source 20; a valve 120 in the fuel passage movable between flow and no-flow positions, means biasing the valve to its no-flow position, means adapted for connection in the engine starter circuit to respond to engine cranking to move the valve to a flow position permitting the induction of fuel through the fuel port and other means for modulating the rate of flow of fuel through said fuel passage as a function of an engine-related temperature. The valve 120 is closed by a spring and opened by a solenoid 122 when the ignition switch is at its start position. The flow-rate of fuel permitted through the passage controlled by valve 120 is determined by a cranking valve 100, whose position is determined by the temperature sensed by a bi-metal spring 300, Fig. 4, which responds by causing movement of levers 292 and 216 and link 174. When the engine starts, the solenoid 122 is de-energized e.g. by return of the ignition switch to the on-position or by a manifold vacuum switch. When starting from cold, lever 292, Fig. 4 which is fixed on a shaft 218, will be in its extreme clockwise position with end 297 at the upper end of a slot 304, thus rotating a lever 216 which is also fixed on shaft 218 to turn a fast idle cam 224 which is rotatable on shaft 218, clockwise to locate cam step 230 opposite the end 234 of a throttle lever 232, rotatable on throttle shaft 24 and biased clockwise by throttle return spring 242 acting via a linkage 240 fixed to the shaft 24 and a tong portion 236 of lever 232. By rotating the throttle valve in its opening direction (i.e. anticlockwise), end 234 is moved away from the fast idle cam allowing a servo spring 288, Fig. 4, acting by way of bell-crank 264 and link 262 to rotate a lever 258, which is rotatably mounted on shaft 218, so as to insert a finger portion 254 pivotally attached thereto between cam step 230 and lever 232. The throttle plates 25 are therefore at their maximum opening start position. Since the lever 216 is in its extreme clockwise position, link 174, Figs. 4 and 5, is in its lowest position, so needle 140 and valve 100 are raised and a needle valve 72 is in its lowest position. Raising of needle 140 provides maximum flow cross sectional area at a valve seat 150 above which is a chamber 152 from which fuel passes via passages 154, 158, Fig. 7, to passages 128 in parallel with the starting fuel flow via passages 112, 114 &c. Lowering of the needle valve 72 minimizes the flow cross sectional area of a port 63 from a well 62, Fig. 5, connected to the induction passage 10 to sense the Venturi vacuum therein, via passages 60, 58, 56, 54, 52, 42 and 41, see Figs. 5 and 8, to a servo chamber 30. Passage 42 is also connected via a restrictor 46 and a port 50. Fig. 10 (not shown), to a point which is below the throttle valve when in its closed position. During cranking the vacuum in chamber 30, Fig. 3, is not sufficiently large to move diaphragm 32 leftwards to move side wall 12 of Venturi 13 and needle 16 to the left, so the Venturi 13 has its minimum opening, and air-flow velocity past fuel metering jets 18 is relatively high. Once the engine has started, release of the ignition switch de-energizes solenoid 118, so blocking the passage 114, 116 &c. However, while the engine is still cold, the needle valve 72 continues to substantially block port 63 so that it is the engine manifold vacuum which acts via port 50 and passage 42 in servo chamber 30 and causes the Venturis to be opened and the needle 16 moved to the left. With the throttle plates still at the fast idle position, opening the Venturis reduces the air velocity across fuel jets 18 to reduce the fuel metering signal while simultaneously enlarging the jet orifices. Since the cross-sectional area of the fuel passages 128 is constant, the reduced air velocity reduces the fuel metering signal there and reduces fuel flow through these passages, leaving the overall mixture. When the throttle plates are opened, they traverse the port 50, so a lesser vacuum is transmitted to the servo chamber 30 causing the Venturis to move towards a more restricted position so that the mixture is made richer again, but not as rich as when cranking. Once the engine is running, manifold vacuum in servo chamber 272, Fig. 4, will suffice to withdraw finger portion 254 from between lever 232 and fast idle cam 224 so that the throttle plates may close more. As temperature rises, levers 292 and 216 and hence fast idle cam 224 rotate anti-clockwise so that the throttle plates can move to more nearly fully closed positions. Simultaneously, needle valve 140 is lowered to reduce fuel flow and needle valve 72 is raised so that it is predominately the Venturi pressure that is transmitted to the servo chamber 30. When the needle valve 72 is substantially completely removed from port 63, the movement of the Venturi walls 12 is controlled almost entirely by Venturi vacuum. The valve 140 substantially prevents additional fuel supply and the cranking valve 100 is at its minimum cross-sectional area position.