Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Reexamination Certificate
1999-09-30
2001-09-11
Warden, Sr., Robert J. (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
C204S401000, C073S001060, C073S023320, C123S688000
Reexamination Certificate
active
06287453
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for the diagnosis of a continuous-action lambda probe disposed upstream of a catalytic converter of an internal combustion engine.
For controlling the mixture in an internal combustion engine, it is known to provide in the exhaust flow upstream of the catalytic converter, serving for the conversion of harmful exhaust gas constituents, an oxygen sensor or probe, the output signal of which changes in dependence on an oxygen concentration in the exhaust gas.
In addition to so-called sudden-change probes, also referred to as binary probes, the output signal of which changes suddenly both when there is a transition from a rich mixture to a lean mixture and when there is a transition from a lean mixture to a rich mixture (sudden voltage change with the air-fuel coefficient &lgr;=1), oxygen probes with a continuous characteristic curve are also used. These have a continuous, for example linear, dependence of the output signal on the air-fuel coefficient &lgr; and, in addition, a low rise time. (SAE Paper 940149 “Automatic Control of Cylinder Air-Fuel Mixture Using a Proportional Exhaust Gas Sensor”).
Such an oxygen probe with a continuous output characteristic, referred to in the following simply as a continuous-action lambda probe, is constructed for example on the basis of strontium titanate (SrTiO
3
) by thin-film technology (VDI Berichte 939, Düsseldorf 1992, “Vergleich der Ansprechgeschwindigkeit von KFZ Abgassensoren zur schnellen Lambdamessung auf der Grundlage von ausgewählten Metalloxiddünnfilmen” [Comparison Of The Rate Of Response Of Motor Vehicle Exhaust Sensors For Rapid Lambda Measurement On The Basis Of Selected Metal-Oxide Thin Films]).
The use of a continuous-action lambda probe results in the changeover from two-point lambda control to continuous lambda control. In order not to exceed the statutory exhaust-emission limit values, the failure of exhaust-relevant components must be detected and indicated (onboard diagnostics).
It is therefore necessary to check the functioning capability of the lambda probes as well. It is known from Published European Patent Application EP 0 616 119 A1 in the case of a lambda probe disposed upstream of the catalytic converter (pre-cat probe) to measure the switching times within which the output signal of the lambda probe switches over during its sudden-changing function from the high voltage value, which indicates a rich mixture (rich voltage), to a low voltage value, which indicates a lean mixture (lean voltage). The magnitude of these switching times is a measure of the functioning capability of the lambda probe disposed upstream of the catalytic converter.
A further method for checking the dynamic functioning capability of pre-cat lambda probes is described in Published European Patent EP 0 652 358 A2. There, the holding times within which the lambda probe signal indicates a rich or lean mixture are measured. The pre-cat lambda probe is then classified as operating correctly if both the rich and the lean holding times are less than prescribed limit values assigned to the individual holding times.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for the diagnosis of a continuous-action lambda probe which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in which the functioning capability of a lambda probe having an output signal with a continuous characteristic curve and disposed upstream of a catalytic converter in the exhaust flow of an internal combustion engine can be checked in a closed control loop.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for diagnosing a lambda probe disposed upstream of a catalytic converter of an internal combustion engine, the lambda probe outputting an output signal having a continuous characteristic curve received as an input variable of a lambda control loop, the method which includes:
superposing a periodic forced stimulation at a prescribed frequency and amplitude on a required value for an air-fuel ratio;
simulating a system response of the lambda control loop with a model having a sensor delay time as a model parameter;
determining amplitude gains of the model and the lambda control loop and performing a comparison of the amplitude gains with each other;
performing a modification of the model parameter, the sensor delay time, in accordance with a result of the comparison of the amplitude gains; and classifying the lambda probe as defective if a value of the modification of the model parameter exceeds a prescribed threshold value.
For the diagnosis of the lambda probe, forced stimulations are asserted on the closed lambda control loop. A forced stimulation brings about a periodic change in the value of the air-fuel ratio &lgr; by a stoichiometric ratio &lgr;=1 and is described by applicable parameters, such as amplitude and frequency for example. To realize the prescribed situation as exactly as possible in the closed lambda control loop, a compensation of the dynamic response of the controlled system is required. This compensation of the system response can also be used to draw conclusions as to a change in the delay time of the lambda probe. The change in the dynamic response of the lambda probe is observed when there are aging effects or contamination of the probe. The compensation results can consequently be improved by an adaptation of the delay time of the lambda probe. The adaptation of the model parameters of the lambda probe allows the aging and contamination effects of the probe to be taken into account for the lambda control and for the compensation of the system response as well as the detection of a defective lambda probe, if applicable.
For the method described there has to be a continuous-action lambda probe upstream of the catalytic converter. The continuous-action lambda probe is the measuring element of the lambda control, which reduces deviations in the fuel-air ratio from a required value. The required value of the fuel-air ratio, the setpoint value of the control, is superposed with selectively periodic forced stimulations, which are prescribed for example with respect to amplitude and frequency (for example square-wave signal sequences) in such a way that the requirements of the internal combustion engine and the catalytic converter are taken into account in the best possible way. In order to realize in the best possible way the parameters, fixed by amplitude and frequency, of the forced stimulation in the closed control loop of the lambda control, a compensation of the dynamic response of the controlled system under lambda control is required. For an internal combustion engine, the system response can be characterized by the time lag between the load signal and the measured value acquisition of the lambda probe and the dynamic response of the lambda probe as a first-order time delay element. For the modeling of the time lag there are two fundamental possibilities. On the one hand, the time lag may be realized in the engine control by a shift register or the like, considerable expenditure being required for this to be realized on account of the great time lag at low engine speed and load. On the other hand, the time lag may be modeled by a finite-dimensional approximation, such as a Pad-approximation. In both cases, the parameters of the model of the time lag are adapted according to the operating point of the engine as functions of engine speed and load. Even when a low-order Pad-approximation (for example of the second order) is used, the compensation of the system response in the control loop has the effect that the forced stimulation characterized by amplitude and frequency can be realized in wide frequency ranges with minor errors.
It is also known that the dynamic response of the lambda probe changes due to aging and contaminating processes. On the one hand, these changes influence the controlling quality of the lamb
Rosel Gerd
Zhang Hong
Greenberg Laurence A.
Lerner Herbert L.
Olsen Kaj K.
Siemens Aktiengesellschaft
Stemer Werner H.
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