Patent GB-1140751-A (GB)
Title: Improvements in or relating to fuel-air mixture intake systems for internal combustion engines
Inventor: O'NEILL CORMAC GARRETT
IPC: F02M7/17
Filed: 1966-08-12
Abstract: 1,140,751. Spray carburetters. ZENITH CARBURETTER CO. Ltd. Aug. 9, 1967 [Aug. 12, 1966; Oct. 3, 1966; Dec. 20, 1966; Feb. 14, 1967], Nos. 36239/66, 44083/66, 57010/66 and 7033/67. Heading F1B. In an I. C. engine fuel/air intake system including a mixture by-pass 22, Fig. 2 connecting the upstream side of a throttle valve 21 to the downstream side, the by-pass is controlled by a normally-closed obturator valve 23 which is opened in response to the depression in the downstream side when that depression exceeds the depression prevailing in the downstream side when the throttle valve is closed and the engine is running at its normal idling speed. A known air slide valve 12 co-operates with the induction passage 14 to form a throat into which a jet orifice opens, the fuel flow through the jet orifice being controlled by a profiled needle moved by the air slide. The loading of spring 28 may be adjustable. The pressure upstream of throttle valve 21 acts through metering orifice 27 on the upper side of diaphragm 25, the other side of the diaphragm being subjected to the pressure in the downstream part communicated via the by-pass 22 and conduit 31 to chamber 29. The load of spring 28 is chosen so that valve head 24 is not moved off its seat until the downstream depression exceeds a predetermined value, e. g. 15" Hg, which is greater than that prevailing during idling but less than that prevailing during overrun conditions. The slight increase in the total air flow past the air slide valve causes the latter to increase the fuel flow to maintain the correct mixture. In another embodiment a diaphragm 39, Fig. 3 is subjected to ambient pressure in a cavity 37 tending to unseat a valve 43 from its seat 35. The downstream depression acts in cavity 41 to provide a differential pressure across diaphragm 39 which is insufficent to overcome spring 45 to open the by-pass during normal engine idling. When the by-pass is closed the depression acting in bore 34 also tends to keep the valve closed. During overrun conditions the downstream depression increases sufficiently to cause opening of the bypass which in turn eliminates the depression acting in bore 34. The resultant valve opening force is increased and the by-pass remains open even if the downstream depression is slightly reduced. Similary when the by-pass is reclosed it remains closed until a substantial increase in the downstream depression again takes place. When valve plunger 42 is moved it unseats a spring-loaded poppet valve 51 thereby communicating the depression in cavity 41 to a suction-operation ignition retarder (not described). To assist the rapid return to normal ignition timing when the bypass closes the ignition retarder may be normally connected to atmosphere through a calibrated bleed orifice. Alternatively valve 51 may be replaced by an isolating valve which also controls the venting of the ignition retarder. In another embodiment an adjustably spring- loaded valve head (24a), Fig.4 (not shown) closes a passage leading to the upstream side and both the part of the diaphragm side facing the by-pass and the opposite side of the diaphragm are subject to the downstream depression. The valve heads in the embodiments of Figs.2 and 4 may have frustro-conical seats. In another embodiment the by-pass is an aperture (21<SP>b</SP>), Fig. 5 (not shown) in a throttle valve plate (21<SP>a</SP>), which is normally closed by a spring- loaded obturator valve head (24<SP>d</SP>). In a carburetter of the fixed-choke type metered additional fuel is drawn into the by-pass through a non-return valve (72), Fig. 6 (not shown) only when the by-pass passage (63), (64) is open. In another embodiment a valve 92, Fig. 7, separated from the obturator valve 88 opens and closes the connection between chamber 85 and the downstream part of the induction passage in order to reduce "hunting". Under most operating conditions the depression in chamber 103 is insufficient to create a pressure differential across diaphragm 99 sufficient to unseat valve 106 against the loading of spring 107. The ambient pressure acting in chamber 104 on diaphragm 99 is opposed also by the ambient pressure in chamber 102 acting on valve 106. Under overrun conditions the pressure in chamber 103 falls and valve 106 is unseated so that it moves to a position where projection 116 closes bleed orifice 115. The depression is communicated through chamber 102, conduit 113 to chamber 85 so that the higher pressure in the upstream part unseats valve 88 to open the by-pass. The arrangement of Fig. 7 may be used in carburetters of the fixed-choke type. The system may be applied to carburetters and intake systems having more than one induction passage or conduits.