CARBURETOR

1,218,840. Carburetters. K. LÍHNER. June 5, 1968 [June 26, 1967], No. 26732/68. Heading F1B. In a constant-suction type carburetter in which an air piston in a thoat preceding the throttle valve adopts an equilibrium position in which the action of a spring tending to move it across the throat towards a bridge is opposed by a thrust developed by a pressure difference across a pressuresensitive element, means are provided for progressively increasing the effective thrust which opposes the spring action as the throttle valve is closed, below what would be developed by the difference between atmospheric pressure and the pressure in the throat applied across the pressuresensitive element, so as to reuced the distance between the air piston and the bridge. The air piston 2, Fig. 4, is positioned by a diaphragm 23 exposed on its lower side to atmospheric pressure via a duct 3 and on its upper side to the pressure upstream of the throttle valve 20 via a duct 22, the net upward thrust on the diaphragm being opposed by a spring 24. The pressure prevailing at the upper side of the diaphragm 23 is also applied, via a duct 19, to the upper side of a hollow piston 31a sliding within a cylinder 30 and connected to the air piston 2 by a piston rod 29. The lower side of the hollow piston 31a is exposed via a duct 32 to the pressure downstream of the throttle valve 20. When the throttle valve 20 is moved towards its closed position, the resultant reduction of pressure downstream of the throttle valve acting upwardly on the hollow piston 31a causes the air piston 2 to assume a lower position than would otherwise be the case. The resultant increase in the air velocity improves the dispersal of fuel in the air stream. The inlet 21 of the duct 32 may be treated just upstream of the throttle valve 20 when the latter is fully closed. In a modification, Fig. 3 (not shown), the hollow piston 31a is replaced by a solid piston (31), and in the case a damping piston 33 is omitted. In addition, the duct 19 may be replaced by a duct (18) communicating with atmosphere. The pressure applied to the underside of the piston (31) may be modified by inserting in the duct (32) between two restrictors a control valve leading from the atmosphere or from either side of the diaphragm 23. The control valve can be controlled by the throttle valve shaft or by a diaphragm or piston subjected to the pressure downstream of the carburetter. In Fig. 5 (not shown), the hollow piston 31a is replaced by annu