Patent GB-1466396-A (GB)
Title: Arrangement for decontaminating internal combustion engine exhaust gas
IPC: F01N3/20
Filed: 1974-01-30
Abstract: 1466396 Decontaminating IC engine exhaust gases ROBERT BOSCH GmbH 30 Jan 1974 [31 Jan 1973] 04315/74 Heading F1B [Also in Divisions B1-2 and G1] A catalytic reactor 12 for decontaminating I.C. engine exhaust gas is combined with an oxygen measuring sensor 19 having a catalytically inactive, e.g. gold, electrode 23 and arranged to measure the oxygen content of the exhaust gas after it has passed through the reactor and a switching circuit 20 responsive to the sensor's output signal and either connected to actuate a warning device 39 or connected to actuate an adjusting member 34 for inhibiting the operation of the engine or connected to actuate both device 39 and member 34. If the exhaust gas oxygen content indicates failure or malfunction of the reactor, the warning device 39 and/or member 34 operate, the member 34 being, for example a valve which opens to allow exhaust gas recirculation to cause reduction of engine power. A holding device 33 e.g. a relay, may be provided to hold the warning device 39 and/or the adjusting member in the 'on' position once actuated. A second oxygen sensor 38 may be located upstream of the catalytic reactor 12 so that the switching circuit compares the outputs of the two sensors to determine whether a malfunction has occurred. A temperature sensor 37 may be provided to compensate for temperature differences upstream and downstream of the reactor 12. A probe 13 responds to exhaust gas composition to regulate the airfuel ratio by control of a low-pressure intake pipe injection control device 14. The sensors. The sensor 19, Fig. 2, comprises an ion-conducting solid electrolyte 21 of, for example, zirconium dioxide separating coatings of catalytically active and inactive materials 22, 23 such as platinum and gold respectively. The potential difference between the coatings 22, 23 varies with the air-fuel ratio of the mixture fed to the I.C. engine and with the condition of the catalytic reactor. Instead of two sensors 19, 38 of the type just described, a single sensor 90, Fig. 4 may be used. This has two catalytically inactive electrodes 91, 92 subjected respectively to exhaust gas from upstream and downstream of the catalytic reactor by way of valves 95, 96 and lines 93, 94. The electrical signals from the electrodes 91, 92 may be fed to the switching circuit 20 or to a measuring device 97 for indicating the values. The sensor 90 is provided with a thermally insulated housing and is such that satisfactory heat conduction exists between the electrodes 91, 92 and the exhaust gas lines 93, 94. Hot wire detectors (not shown) for measuring combustible components of the exhaust gas upstream and downstream of the catalytic reactor 12 can also be arranged in the housing of the measuring sensor 90. Switching. In Fig. 5 is shown a switching arrangement for actuating the warning device 39 and adjusting member 34, Fig. 1, when the catalytic reactor 12 is impaired or destroyed. The measuring sensor 19 is connected between the inverting input of an operational amplifier 41 in the form of a threshold value switch and the non-inverting input of an operational amplifier 47, whose output is connected to a voltage divider formed by resistors 43, 44 between positive lead 45 and earth and to the non-inverting input of operational amplifier 41. The terminals of temperature sensor 37 are connected across the two inputs of the operational amplifier 47, one being by way of a potential divider formed by resistors 53, 54 connected between positive lead 45 and earth. The output of the  operational amplifier 41 and a sensing device 58, which supplies a signal only when the engine is in a desired operating state, are connected to an AND gate 57. When the output voltage of sensor 19 falls below a threshold value set by the voltage divider 43, 44, the operational amplifier 41 is switched and a signal appears at its output. If the engine is in the desired operating state, the device 58 also supplies a signal so that the AND gate 57 conducts and supplies a signal to actuate the warning device and/or adjusting member. The threshold value is influenced by the temperature sensor 37 varying by way of the operational amplifier 47 the potential at the junction of resistors 43, 44. In Fig. 6 (not shown) the switching arrangement uses two measuring sensors 19, 38 connected so that the difference between their outputs determines the output of operational amplifier 59. If the output of the amplifier 59 falls below the threshold value set by the voltage divider 43, 44 in conjunction with the temperature compensating device, the operational amplifier 41 is switched and a signal appears at one input of AND gate 57. If the engine is in a desired operating condition a signal is supplied to the other AND gate input ensuring that it conducts and that the warning device and/or the adjusting member are actuated. Engine operating conditions. Switch 67 is closed and supplies a signal in dependence upon engine temperature, switch 68 supplies a signal when butterfly valve 70, Fig. 1, is in a specific position and switch 69 supplies a signal when a specific vacuum exists in the engine induction manifold 36. When all three switches are closed, the AND gate 71 produces an output signal and signals are supplied to both inputs of an AND gate 74 whose output is fed via terminal 82 to the input of AND gate 57 Figs 5 and 6 (not shown). When one of the switches 67, 68, 69 supplies no signal, the AND gate 74 ceases to conduct and no signal is fed via the terminal 82 to the AND gate 57 so that triggering of the warning device 39 and/or the adjusting member 34 is prevented.