Patent GB-752596-A (GB)
Title: Improvements in tachometric carburettors for internal combustion engines
IPC: F02M69/00
Filed: 1954-06-21
Abstract: 752,596. Carburetters. SOC. DU CARBURATEUR ZENITH. June 21,1954 [June 25,1953], No. 18162/54. Class 7(3) A carburetter comprises a volumetric fuel pump driven at engine speed or in relation therewith and a metering device dividing into two parts the fuel flow supplied by the pump to a fuel inlet chamber, one of the parts being despatched into an injection duct through a calibrated injection passage, the injection duct being connected to an injector opening into the engine inlet manifold, while the other of the parts is despatched into return duct through a calibrated return passage, the pressure in the return duct being regulated by a valve disposed in the return duct downstream of the calibrated return passage and controlled by a pressure regulator actuated responsive to the pressure differential between the injection duct and the return duct, the ratio between the cross-sections of the calibrated injection passage and of the calibrated return passage being regulated responsive to the engine inlet pressure and a pressure responsive device responsive to the engine inlet pressure simultaneously so regulates the calibrated injection passage and the calibrated return passage as to increase the cross-section of the calibrated injection passage and to reduce the cross-section of the calibrated return passage when the inlet pressure increases and conversely. Fuel under pressure from a pump, Fig. 1 (to be described later) enters at 18, Fig. 2, and part thereof flows through an orifice 27 to a pipe 32 leading to a nozzle 118 in the induction pipe (Fig. 4) and part flows through a return orifice 26 into a passage 36 leading back to the fuel tank or the pump inlet. The orifices are controlled by a profiled valve 59 which in turn is controlled by a capsule 61 in a chamber 62 connected by a pipe 67 to the induction pipe downstream of the throttle valve and by a pipe 68 to a space 69, Fig. 4. During normal operation the pipe 68 is cut off from the intake. The valve is also controlled by a piston 72 acted on by the pressure in the chamber 62 and by the atmospheric pressure communicated through a filter 76. The valve 59 is designed so that the sum of the flow cross-section of the orifice 27 and the flow cross-section of the orifice 26 remains substantially constant. There may be as shown a by-pass 83, 84 across the orifice 26 and including an orifice 85 controlled by a valve 88 which is under the influence of a bimetallic coil 92 which operates a cam 89. Consequent on increase of manifold temperature, the suction of the orifice 85 is increased. The by-pass and thermostatic control can be deleted. A valve 37 operated by a piston 41 is fitted to maintain the pressures in the passages 31, 36 substantially equal. When the throttle is near its closed position the suction is high so that air is sucked from the air intake 100 towards the aerated fuel outlet 118 through the pipe 108. Thus air flows at great speed and ensures satisfactory fuel atomization. Tangential slots 119 are provided. The fuel flows through helical grooves in a member 113. An accelerating pump comprises a fuel chamber 120. It is actuated by a lever 122 connected by a link 123 to the throttle lever 102. Operation of the pump causes an injection of fuel through the nozzle and also produces a pressure increase which is transmitted through the pipe 32 to the injection passage 31 and to the upper face of the piston 41. As a result of this pressure increase the piston 41 closes the return pipe 36 and a greater quantity of the pump delivery is supplied to the injector. The engine can be stopped by opening a valve 47. The fuel supplied corresponds to the theoretical quantity required. As it is particularly desirable to enrich the mixture upon reaching the region of full load operation the profile of the valve 59'may be modified for this purpose. If the carburetter is to operate at ground level connection of the fuel delivery in dependence on exhaust back pressure may be omitted. Thus the cover 81, Fig. 2, containing the piston 72 and rod 74 may be omitted and replaced by a solid cover. At small throttle openings enrichment of the mixture is effected by opening the valve 127. Air from the intake is admitted into the chamber 62 containing the capsule 61 causing movement of the valve 59 in a sense to increase the fuel flow. To enrich the mixture during starting and cold running a valve 133 is opened thus placing the capsule chamber 62 in communication with the air intake 100. If the capsule 61 bursts the valves 59 is urged towards the left into a position necessary to ensure full throttle operation at ground level. The pistons illustrated may be replaced by flexible diaphragms and vice versa. The piston 72 can be omitted and replaced by a small secondary capsule disposed in the chamber 62 and interposed between the capsule 61 and the shank 63, the interior of the secondary capsule being connected to atmosphere. When the carburetter is' intended to operate at ground level it is possible for the capsule 61 to be replaced by a flexible diaphragm which closes the chamber 62. The profile of the needle 59 may be modified and can be so determined that the sum of the flow cross-section of the orifices 26, 27 is not constant. Fig. 1 shows the fuel pump comprising two gear pumps 5, 6, 15, 16 in series. The primary pump could run at half engine speed or engine speed. The secondary pump is driven for example at half engine speed. The delivery of the primary pump is greater than the delivery of the secondary pump. A bypass valve 12 assumes such a position that the pressure difference between the chamber 7 and the chamber 17 substantially balances the force of the spring 13. It is stated that the delivery pressure of the pump 16 can be less than the input pressure. There is a substantially constant pressure differential between the input chamber 9 and the delivery chamber 17 and the pump delivery is proportional to engine speed. A valve 52 enables the chamber 33 to be connected to atmosphere to enable air in the fuel pipping to be removed when the engine is started. Fuel leaks are drained off through a tube 80. The advantages of the variable discharge orifice compared to a fixed discharge orifice are explained.