Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
1999-10-08
2001-08-21
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S687000, C701S109000
Reexamination Certificate
active
06276349
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Application No. 198 46 393.6, filed Oct. 8, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a cylinder-selective control of the air-fuel ratio in the case of a multi-cylinder internal-combustion engine as well as to a system for implementing-such a cylinder-selective control.
It is known that a controlled catalyst operation is required for a high conversion rate of the pollutants present in exhaust gases. In this operation, the exhaust gas composition is monitored by a lambda probe and, in the event of a deviation from an air ratio &lgr;=1, the air-fuel composition is corrected.
The lambda probe is normally installed as a sensor in the exhaust gas flow in front of the catalyst, specifically behind a junction of the exhaust pipes from the individual cylinders. As a result, the lambda probe supplies an averaged value concerning the individual cylinders. However, as a rule, mixture fluctuations between the individual cylinders are not compensated and cause a deterioration of the emissions for two reasons. On the one hand, the control frequency of the lambda control is shortened by mixture differences. This falsifies the average lambda value set by way of control parameters. On the other hand, the flows from the individual cylinders, as a rule, flow against different areas of the catalyst. As the result of the mixture differences, these areas do not operate in the optimal lambda range.
European Patent documents EP 0 670 419 A1 and EP 0 670 420 A1 describe systems for estimating the air-fuel ratio in the individual cylinders of a multi-cylinder internal-combustion engine. By means of these systems, the mixture fluctuations between the individual cylinders are taken into account. In this case, a mathematical model is developed in order to describe the system performance as a function of an output signal of a broad-band air-fuel sensor. An observation of the development of the condition of the mathematical model supplies information on the air-fuel ratio in the individual cylinders, whereupon a corresponding adjustment of the fuel-air ratio can be performed for each cylinder.
However, the above-described process requires relatively high computing expenditures and is based on the signals of broad-band lambda probes.
It is an object of the invention to provide a simple, cylinder-selective control of the air-fuel ratio in the case of multi-cylinder internal-combustion engines of the above-mentioned type, which operates reliably for a long operating period and whose development and securing expenditures are lower. In addition, a reasonable system is to be obtained.
This object is achieved by a cylinder-selective control process of the air-fuel ratio in the case of a multi-cylinder internal-combustion engine, wherein a lambda probe arranged in the exhaust pipe system generates a voltage signal corresponding to an air-fuel ratio. The voltage signal is supplied to a computing unit which determines the air-fuel ratio for each individual cylinder. A fuel metering unit determines a fuel injection quantity at least as a function of a basic fuel injection value and the determined air-fuel ratios of the individual cylinders. A fuel supply unit supplies the fuel injection quantity determined by the fuel metering unit to the cylinders of the internal-combustion engine. The computing unit crank-angle-synchronously detects the voltage signal and assigns it to a certain cylinder. A voltage deviation is determined for each cylinder in relation to the voltage signals of the adjacent cylinders. A correction of the injection quantity is carried out as a function of the voltage deviation.
The object is further achieved by a system for implementing the cylinder-selective control of the air-fuel ratio in the case of a multi-cylinder internal-combustion engine, wherein a lambda probe is provided in the exhaust pipe system for generating a voltage signal corresponding to an air-fuel ratio, a determination unit is provided to which the voltage signal is fed in order to determine the air-fuel ratio for each individual cylinder, a fuel metering unit is provided which determines a fuel injection quantity at least as a function of a basic fuel injection value and the determined air-fuel ratios of the individual cylinders, and a fuel supply unit is provided which supplies the fuel injection quantity determined by the fuel metering unit to the cylinders of the internal-combustion engine. The determination unit is constructed for (1) detecting the voltage signal in a crank-angle-synchronous manner and assigning it to a certain cylinder, (2) determining the voltage deviation for each cylinder in relation to the voltage signals of adjacent cylinders, and for (3) carrying out a correction of the injection quantity as a function of the voltage deviation.
In order to minimize mixture fluctuations between the cylinders, working-cycle-synchronous voltage fluctuations of the lambda probes selected in the form of surge probes are analyzed and are assigned to the individual cylinders. In particular, the voltage deviation of the lambda probe voltage signal of a cylinder is formed in relation to the voltage signals of the—relative to the ignition sequence—adjacent cylinders. By means of the differential value, a correction of the injection will then be made.
According to a preferred embodiment of the invention, a correction value for the injection quantity is obtained from a characteristic curve or a characteristic diagram.
In order to reduce the computing expenditures, the cylinder-individual mixture adaptation may be switched off above a defined threshold.
Preferably, two correction values per cylinder are computed for the injection quantity, for example, one term for long-period deviations and one term for short-period deviations (such as tank ventilation).
If defined conditions are met for lambda adaptation, the long-period term can form an adaptation value for the cylinder mixture adaptation and, after the engine is switched off, can be stored in the holding phase of the control unit in a non-volatile manner.
On the whole, the present invention has the advantage that a long operating period with high control precision can be used as the basis. In addition, surge probes are clearly lower in cost than broad-band lambda probes, so that generally lower development and manufacturing costs can be expected.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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Albrecht Florian
Kofler Franz
Meder Georg
Argenbright Tony M.
Bayerische Motoren Werke Aktiengesellschaft
Crowell & Moring , L.L.P.
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