GB1506634A - Strating facilities in internal combustion engine carburettors - Google Patents

Abstract

1506634 Automatic choke carburetters SOC INDUSTRIELLE DE BREVETS ET D'ETUDES 22 May 1975 [27 May 1974] 22357/75 Heading F1H To control the opening speed of an eccentrically mounted choke valve 7, biased against opening by an engine temperature sensitive bi-metallic spring 9 and opened by a vacuum motor 28 upon starting an engine, there is provided, between the vacuum motor 28 and an induction pipe 1, a vacuum transmitting duct 11 having a throttling restriction 38 and opening into the induction pipe 1 at a first position 37, which is always downstream of a throttle valve 2, and also at at least one other position 41a, 42a, which may or may not be upstream of the throttle valve minimum opening position depending upon the ambient temperature. The minimum opening position of the throttle valve is limited by a fast-idle cam 19 rotated by a bi-metallic strip 20. At low ambient temperatures e.g. -20‹C all the ducts 37, 41, 42 open into the induction pipe 1 below the throttle valve 2, so that a high degree of vacuum is transmitted to the motor 28 enabling the choke valve 7 to open at a speed limited by throttling restriction 38 against the bias of an engine temperature dependent spring force from the bi-metallic spring 9. At higher engine temperatures e.g. +20‹C this biasing force is smaller and thus without modulating the vacuum applied to motor 28, the choke valve 7 would open too quickly. Consequently at higher temperatures the fast-idle cam 19 limits the throttle valve minimum opening so that at least some of the ducts 41, 42 open into the induction pipe 1 upstream of the throttle valve 3 to reduce the magnitude of the vacuum acting on the motor 28. The separate ducts 41, 42 may be replaced by a single vertical slot (not shown), communicating with the vacuum transmitting duct 11 near the slot base.