Patent GB-1529632-A (GB)
Title: Internal combustion engine
IPC: F02M7/24
Filed: 1976-02-19
Abstract: 1529632 Spray carburetters NISSAN MOTOR CO Ltd 19 Feb 1976 [6 March 1975 8 March 1975 11 March 1975] 06543/76 Headings F1B and F1H I.C. engine 10, 12 has a mixture supply system 16 and an exhaust pipe 20 leading to a three-way catalytic reactor 22, which requires the air/fuel ratio of the mixture fed to the cylinders to be kept close to 14À8:1. To control the air/fuel ratio a sensor 24, sensitive to e.g. the concentration of oxygen in the exhaust gases, is provided. The electrical signal from the sensor is compared with a signal representing a ratio of 14À8:1 and a control signal is produced by circuit 26 which operates extra air and/or fuel valve 28. The control signal is a train of pulses which cause the valve to open and close at a frequency and for durations which will provide the desired ratio, the basic mixture supplied being richer than stoichiometric. Fig. 5 shows a carburetter in which the main nozzle 74 and the slow-running nozzle 86 are fed from float chamber 56. A solenoid-operated valve 28a admits air through an inlet 98a and an outlet 100a to emulsion tube 66. A similar valve 28b admits air to tube 80 of the slow-running circuit. The valves are opened by pulses from control circuit 5c. In a modification the valves are designed to linearly vary the rates at which air enters the main and slowrunning systems, and the control circuit is modified to produce an analogue signal representative of the signal produced by the sensor 24. In a further modification, Figs. 10 and 11 (not shown) the air admission valves are actuated by the vacuum in the intake manifold and the solenoid valves are controlled by circuit 5c to determine the degree to which the air admission valves are actuated by the vacuum. Alternatively the valves may control the fuel flows in the main and slow-running circuits, in which case they operate to reduce the amount of fuel supplied, or they may control both the fuel and the air supplies. Since the amount of any one constituent of the exhaust gases downstream of the reactor is proportional to the amount upstream of the reactor, the sensor may be located downstream of the reactor. In a further modification, air is admitted to the exhaust pipe, upstream of sensor 24, by providing an opening into the exhaust pipe which is controlled by an automatic reed valve, which allows atmospheric air to enter the exhaust pipe during the regular periods when sub-atmospheric pressure exists in the pipe, Fig. 8, (not shown). In a further modification, Fig. 9, the control circuit 5c is used to actuate valve 140 which admits air into the exhaust pipe at a rate dependent on the signal emanating from sensor 24. To reduce the proportion of oxides of nitrogen in the exhaust gas, recirculation of exhaust gas is provided for by passage 108 containing flow control valve 110 which is responsive to the load on the engine, Figs. 2 and 7, and allows maximum flow when the engine is accelerating at full throttle. Fig. 7 also shows a pump 112, able to supply air via flow control valve 118 and check-valve 120, to exhaust pipe 20. Flow control valve 118 is responsive to intake manifold vacuum, or throttle valve angle, or the signal from sensor 24. To prevent a temporary increase in unburnt hydrocarbons and carbon monoxide during deceleration, air is taken from pump 112 through branch line 122 which includes valve 124, biased to the closed condition and arranged to open only at an incipient stage of deceleration. Alternatively the line 122 may have an inlet end open to atmosphere so that fresh air is sucked into the manifold under decelerating condition of the engine.