Patent GB-1374185-A (GB)
Title: Exhaust gas detoxification system
IPC: F01N3/26
Filed: 1972-11-23
Abstract: 1374185 Treating exhaust gas ROBERT BOSCH GmbH 23 Nov 1972 [24 Nov 1971] 54234/72 Heading F1B An exhaust gas detoxification system for mixture-compressed, separately-ignited, fuel injection I. C. engines having an exhaust pipe incorporating a thermo-reactor and a catalyst in which during warming up of the engine the amount of secondary fuel fed to the thermoreactor and, when the engine has attained its operating temperature, the amount of primary fuel injected, is regulated in response to a signal from an oxygen probe in the exhaust pipe.  The thermo-reactor 4 is used only prior to starting the engine to bring the catalytic reactor 6 up to working temperature, so that the limiting value of toxic components in the exhaust gas discharged to atmosphere is not exceeded during the time that the engine is running on a rich mixture. Air enters pipe 1, and exhaust gas leaves the cylinders of an engine 2 by exhaust pipe 3 and passes through thermo-reactor 4, prior to entering the catalytic reactor 6. Oxygen probe 5 projects into the exhaust pipe upstream of the catalytic reactor. Air is supplied to thermoreactor 4 by pump 7 and fuel is supplied through nozzle 9 at a rate controlled by a slide valve 12. Fuel is pumped to an inlet 15 and leaves by a port 14, the effective aperture of which is controlled by the valve 12. A passage 16 leads to one side of a spring-loaded flat seat diaphragm valve. The other side of which faces a chamber 19 which is filled with fuel through a passage 20. Valve 12 is biased by a spring 27 to a position in which the port 14 is closed and fuel pressure from a duct 28 acts on the opposite end of the valve. An electrical switching device 33, when energized holds the valve 12 in a position in which a weak mixture is supplied to the thermoreactor during pre-heating, so that pollutants do not appear in the exhaust gas produced during pre-heating. After pre-heating, when the catalyst has reached its operating temperature, the engine is started and the device 33 is de-energized, an amount of secondary fuel necessary to maintain a stoichiometric ratio being supplied to the thermo-reactor thereafter by controlling the pressure in the duct 28, by the oxygen probe 5 through a valve 36, which comprises a shuttle valve 39 having a fuel inlet 37, an outlet leading to the duct 28 and a further outlet through which fuel is supplied by a line 62 to a fuel metering and distribution valve 65 which supplies the engine fuel injectors. After the engine has been started and while it is warming-up the valve 39 is in the position shown in the Fig. in which fuel can pass directly from the inlet 37 to the duct 28. Fuel also passes to passage 40 from which it reaches drain passage 41 via a flat-seat diaphragm valve 42. The opening of this valve is controlled by solenoid coil 54 which pulls the valve against a spring 48, the current in the coil being regulated by the oxygen probe 5. When the engine has reached its working temperature, an electrical device 61 moves the valve 39, to interrupt the supply of fuel to the duct 28 and to permit fuel to flow to the line 62 and hence through a restrictor 63 into a chamber 64, where it acts on the end face 66 of a shuttle valve 67, in opposition to a force which is proportional to the amount of air passing into the induction pipe 1. The supply of fuel to the injectors is maintained at or near the stoichiometric amount required, during subsequent operation of the engine by the action of the oxygen probe varying the coil current and hence the position of the valve 42.