Patent GB-1486472-A (GB)
Title: Carburettors
IPC: F02M1/00
Filed: 1974-09-06
Abstract: 1486472 Carburetter automatic choke valves HONDA GIKEN KOGYO K K 6 Sept 1974 [7 Sept 1973] 39081/74 Heading F1H An I.C. engine includes a carburetter which comprises a choke valve 4, temperature sensitive means, bi-metal spring 16, for positioning the choke valve in dependence upon temperature when the engine is running, closing means, spring 30, rod 29, adapted and arranged to operate when the engine is stopped so as to move the choke valve in the closing direction from a position determined by the temperature sensitive means; and means diaphragm 27, adapted and arranged to remove the effect of the closing means when the engine reaches a state of substantially even firing after starting, whereby the choke valve can open to a position determined by the temperature sensitive means and subsequent movement of the choke valve 4 while the engine is running is independent of the closing means. The bi-metal spring 16 is connected to the choke valve to apply a closing torque thereto, which increases as temperature falls below a predetermined temperature T, see Fig. 6 (not shown), and a heater 18 is provided to heat the bi-metal spring. Before starting from cold, diaphragm 27 of actuator 25 is in its right hand position so that the closing torque applied to choke valve 4 by the bi-metal spring 16 is greatest. On cranking, the pressure in chamber 26 falls and opens the choke valve to a degree that depends upon the temperature so that the mixture strength is greater the lower the temperature. On starting, the choke valve is opened by a predetermined amount by the diaphragm 27 and the heater 18 is energized to heat the bi-metal spring 16 and open the choke valve 4 further. An electromagnetic actuator may be used in place of vacuum actuator 25. When the throttle valve 5 is opened by cable 10, a connecting rod 41 attached to driving crank 42 on the shaft 7 actuates a bell-crank 40 to engage an arm 222 of choke driving lever 22, which acts by way of bi-metal spring 16 to open the choke valve 4 if it is not already open so that sufficient air reaches the engine under full throttle conditions even when cold. A fast idling system 38 includes a lever 44 mounted on a shaft 43 and biased by a spring 52 so that a screw 46 abuts an operating rod 48 of a temperature sensor 47 responsive to engine coolant or lubricant temperature. One end of lever 44 co-operates with a boss 45a on an arm 45 to move the throttle valve 5 moderately when the coolant or lubricant temperature is low to give a fast idle. Expansion of wax 50 in a canister 49 as the temperature rises allows the throttle valve to move to its minimum opening position. A lever 57 has an arm 58 which engages in a groove 59 of the lever 44 and a hook 57a which moves to the right as shown in Fig. 1 to engage an arm 221 of lever 22 to hold the choke valve in its wide open position so that when the engine is switched off and the heater 18 thereby de-energized the choke valve does not close as the bi-metal element 16 cools but is kept open until the coolant or lubricant temperature falls enough to allow the hook 57a to disengage from the arm 22 1 . In a modification Figs. 4 and 5 (not shown), rod (129) actuated by vacuum actuator 25 engages a contact arm (24a) integral with lever 24 instead of acting though the bi-metal element 16.