Siemens Automotive SA Siemens AG
The method of W09309335 (1993) and US5487269 (1996) is applied for the layout of fig. 76 and is explained with the help of fig. 77.
Fig 76 shows an internal combustion engine equipped with an air filter, an air inlet duct and a throttle valve for regulating the inlet air flow rate, downstream of which there is an inlet pressure sensor which supplies a signal to a computer (CPU). A sensor for the speed of the engine, fixed facing a flywheel of this engine, supplied a second signal to the computer. The latter receives a third signal supplied by an oxygen probe 1 placed in the pipe of the exhaust gases of the engine, upstream of a three-way catalytic converter.
The computer comprises electronic signal processing, calculation and memory means necessary for controlling the opening time /,, or injection time, of one or more fuel injectors. The assembly constitutes a closed-loop regulation (feedback) device for this injection time, the loop being closed by the third signal supplied by the oxygen probe 1.
- Fig. 76 (from W09309335)
A second oxygen probe 2 is placed downstream of the catalytic converter. This probe is of the conventional type supplying a signal which switches between two levels when the oxygen content of the exhaust gases passes through a predetermined threshold. When such a probe is placed upstream of the catalytic converter, the threshold corresponds to a composition of exhaust gases resulting from the combustion of a strictly stoichiometric air/fuel mixture. The signal supplied by the probe 2 is used by the computer for the purposes of the present inventions. To this end, the computer is loaded with specific software suitable for executing the various stages of the methods according to the inventions.
According to the method, in a closed loop control and at a stabilized speed, the mean injection time tlm (time t, of opening of fuel injector) is measured (fig. 77b). During a first interval At/, an open loop control takes place with a forced variation of the fuel injection time lt about tm of deviation corresponding to the limits Qmm and Qmxi of the oxygen storage capacity of the catalytic converter in a non-deteriorated state. If this deviation is off-centered so that only the lower limit Qmn (fig. 77e) of the quantity of oxygen that can be stored is attained, the output signal V02 of the downstream oxygen sensor (fig. 77f) is blocked during the time interval At/ at its high level (some oxygen remains in the exhaust gases at the outlet of the catalytic converter). During a following interval At?, the injection time tii2 is modified in a direction, which tends to unblock the signal. Two different conditions can be distinguished:
a) The output signal of the downstream sensor starts oscillating (fig. 770 The two limits Qmm and Qmia are exceeded and the variation (()m„ -Qmm ), namely the current capacity of the catalytic converter is too low and the catalytic converter is deteriorated (fig. 77e)
b) The two limits Qmm and Qmxt are not attained and the output signal V(>2 of the downstream oxygen sensor remains blocked at the starting
The method of EP0626506 (1994) is applied during a specific time interval and comprises the following steps:
1) determining the number of times nR during which both the output signals of the upstream and downstream sensors indicate a rich air/fuel ratio
2) determining the number of times n, during which both the output signals of the upstream and downstream sensors indicate a lean air/fuel ratio
3) determining from both nH and n, the minimum value nmm = min(nL,nR)
4) comparing nmm to a predetermined limit value e
5) judging that the catalytic converter is deteriorated when nmm > e
The method of W09420737 (1994) presents the case of monitoring during start-up the efficiency of an electrically heated catalytic converter (EHC) placed upstream of a normal three-way catalytic converter (fig. 78).
secondary air ^Hl EHC
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