EP0992666B1 - Cylinder-selective regulation of the air/fuel ratio - Google Patents

Description

The invention relates to a cylinder-selective control of the air-fuel ratio in a multi-cylinder internal combustion engine and to an apparatus for carrying out such a cylinder-selective control according to the preambles of claims 1 and 7, respectively.

It is known that controlled catalyst operation is required for a high rate of conversion of the pollutants present in the exhaust gases. In this case, the exhaust gas composition is monitored by a lambda probe, and with a deviation from an air ratio λ = 1, the air-fuel composition is corrected.

The lambda probe is usually installed as a sensor in the exhaust stream in front of the catalyst and that after a merger of the exhaust pipes of the individual cylinders. Thus, the lambda probe delivers an averaged value over the individual cylinders. Mixture variations between the individual cylinders are usually not balanced and cause emission degradation for two reasons. On the one hand, the control frequency of the lambda control becomes due to mixture differences shortened. This falsifies the mean lambda set via control parameters. On the other hand, the individual cylinders usually flow to different areas of the catalyst. Due to the mixture differences, these areas do not work in the optimal lambda range.

In the EP 0 670 419 A1 and the EP 0 670 420 A1 For example, systems for estimating the air-fuel ratios in the individual cylinders of a multi-cylinder internal combustion engine are described. With this system, the mixture fluctuations between the individual cylinders should be taken into account. A mathematical model is developed to describe the system behavior as a function of an output signal of a broadband air-fuel sensor. An observation of the evolution of the state of the mathematical model gives an indication of the air-fuel ratio in the individual cylinders, whereupon a corresponding fuel-air ratio change can be made for each cylinder.

However, the method described above is relatively computationally intensive and relies on the signals from broadband lambda probes.

Furthermore, from the EP 0 408 206 A2 a generic method and a generic device for correcting the air / fuel ratio for individual cylinders of an internal combustion engine known.

The object of the invention is to provide a simple cylinder-selective control of the air-fuel ratio in a multi-cylinder internal combustion engine of the type mentioned, which is functionally reliable over a long period of operation and their development and hedging costs less. Furthermore, pay attention to a cost-effective system.

This object is achieved by the features mentioned in claims 1 and 7 procedural or device technology.

In order to minimize the mixture variations between the cylinders, the operating cycle synchronous voltage fluctuations are in the form of Jump probes selected lambda probes evaluated and assigned to the individual cylinders. In particular, the voltage deviation of the lambda probe voltage signal of a cylinder in relation to the voltage signals of the - related to the firing order - adjacent cylinder is formed. The differential value is then used to correct the injection.

According to a preferred embodiment of the invention, a correction value for the injection quantity is taken from a characteristic curve or a characteristic diagram.

In order to reduce the computational load, the cylinder-specific mixture adaptation above a fixed limit number could be switched off.

Preferably, two correction values for the injection quantity are calculated per cylinder, for example a term for long-term and a term for short-term deviations (for example tank venting).

The long-term term can form an adaptation value for the cylinder mixture adaptation upon fulfillment of predetermined conditions for a lambda adaptation and be stored non-volatile after engine shutdowns in the holding phase of the control unit.

Overall, the present invention has the advantage that it can be assumed that a long service life with high control accuracy. Furthermore, jump probes are significantly cheaper than broadband lambda probes, so that generally lower development and production costs are to be expected.

Fig. 1

einen schematischen Aufbau einer Vorrichtung zur Durchführung der erfindungsgemäßen zylinderselektiven Regelung und

Fig. 2

ein Zeitspannungsdiagramm bei einer Lambda-Sprungsonde.

The invention will be explained in more detail with reference to an embodiment and with reference to the accompanying drawings. The drawings show in

Fig. 1

a schematic structure of an apparatus for carrying out the inventive cylinder-selective control and

Fig. 2

a time-voltage diagram in a lambda jump probe.

In Fig. 1 a device for carrying out the cylinder-selective control according to the invention is shown. In this case, an engine 10 has a plurality of cylinders. In the present case, the engine 10 has four cylinders.

The engine 10 is supplied via an inlet tract 12 with air, wherein the amount of air is determined by an air flow meter 16. A corresponding signal is output to a control unit 24.

The exhaust gases of the engine are discharged via an exhaust tract 14 to the environment.

In the exhaust system, a catalyst 18 is provided for the conversion of pollutants into non-toxic substances. Between the engine 10 and the catalyst 18, a lambda probe 30 is arranged, which is designed as a jump probe. The lambda probe emits a voltage signal corresponding to the exhaust gas composition to the control unit 24. For example, for a lean mixture (λ> 1), the probe voltage is around 100 mV. In the range λ = 1, the probe voltage changes almost abruptly and reaches values of 800 mV and above for a rich mixture (λ <1). Especially the strong change of the probe voltage in the range λ = 1 makes it possible to detect even small deviations from the optimal air-fuel ratio. The present Invention is based on the fact that the jump manifests itself in a rapid increase in voltage, but not in a pure Rechteckspungcharakteristik. Moreover, it is known that jump probes are very reliable and inexpensive.

In the present case, the control unit 24 also receives temperature values T of the coolant, rotational speed values n via the rotational speed of the engine and an operating voltage U _B.

Since in the present invention, the voltage fluctuations of the lambda probes are evaluated and assigned to the individual cylinders, it is necessary to know the currently available working cycle of each cylinder. For this purpose, a crankshaft sensor 32 is used in the present signal, whose signals are also delivered to the control unit 24.

The control unit 24 calculates an injection time t _i for each cylinder on the basis of the available information and forwards it to injection valves 20. The injection valves 20 supply the fuel received from a fuel supply 22 via lines 26 corresponding to the injection time t _i to the cylinders operating in the engine 10.

The controller 24 first calculates an injection time for each cylinder based on the data available to it, such as temperature T, speed n, and air quantity signals, and generates a basic injection time ti_zyl_z, where the letter z designates a particular cylinder. At this Grundeinspritzzeit then a cylinder-specific mixture adjustment is calculated and that from the difference of two - based on the firing order - adjacent cylinder.

This will be explained below Fig. 2 explained. In Fig. 2 a probe voltage signal ULS_1_z over time S is shown. In the course of the voltage, the probe voltage is indicated for different cylinders z.

The voltage deviation of a cylinder z is now calculated on the basis of the voltage values of the cylinders adjacent to the ignition sequence. The voltage difference for the first cylinder (z = 1) ULS_1_diff_1 is calculated as follows: $$\mathrm{ULS\_}1\mathrm{\_diff\_}1=\left(\left(\mathrm{ULS\_}1\_3+\mathrm{ULS\_}1\_2\right)/2\right)-\mathrm{ULS\_}1\_1.$$

Where ULS_1_z is the probe voltage on the zth cylinder. Accordingly, the differences ULS_1_diff_z are calculated for the other cylinders.

In accordance with the determined voltage deviation, an injection correction KF_ti_zyl_z is taken from a characteristic curve. With this correction injection time, the basic injection time ti_zyl_z is corrected.

If the conditions for a lambda adaptation are met, an adaptation value of the cylinder mixture adaptation is formed and stored non-volatile.

Overall, with the present invention, a simple and cost-effective way of a cylinder-selective control is given.

Claims (7)

1. Cylinder-selective control of the air fuel ratio of a multi-cylinder internal combustion engine, wherein

   - a lambda probe (30) in an exhaust duct generates a voltage signal corresponding to an air-fuel ratio,

   - the voltage signal is supplied to a calculation unit (24) which determines the air-fuel ratio for each individual cylinder,

   - a fuel distribution unit determines an amount of injected fuel, at least in dependence on a basic fuel injection value and the measured air-fuel ratio of the individual cylinder,

   - a fuel supply unit (20) supplies the amount of injected fuel determined by the fuel distribution unit to the cylinders of the internal combustion engine (10), and

   - the calculation unit (24) determines the voltage signal in synchronism with the crank angle and allocates it to a particular cylinder,

   characterised in that

   - for each cylinder a voltage deviation is determined in relation to the voltage signals from the neighbouring cylinders, as regards the ignition sequence,and

   - the amount injected is corrected in dependence on the voltage deviation.
2. Cylinder-selective control according to claim 1, characterised in that a corrected value for the amount injected is taken from a characteristic or a performance graph.
3. Cylinder-selective control according to claim 1 or 2, characterised in that a jump or snap probe in the form of a lambda probe (30) is used.
4. Cylinder-selective control according to any of the preceding claims, characterised in that above a given limiting speed of revolution, the correction is not made.
5. Cylinder-selective control according to any of the preceding claims, characterised in that two corrected values for the amount injected are calculated for each cylinder.
6. Cylinder-selective control according to any of the preceding claims, characterised in that the corrected value is stored in a non-volatile memory.
7. A device for cylinder-selective control of the air-fuel ratio in a multi-cylinder internal combustion engine according to any of claims 1 to 6, wherein

   - a lambda probe (30) in the exhaust duct generates a voltage signal corresponding to an air-fuel ratio,

   - a determination unit (24) is supplied with the voltage signal in order to determine the air-fuel ratio for each individual cylinder, wherein the determination unit (24) is constructed in order to determine the voltage signal in synchronism with the crank angle and assign it to a particular cylinder,

   - a fuel distribution unit determines an amount of injected fuel at least in dependence on a basic fuel injection value and in dependence on the measured air-fuel ratio, and

   - a fuel supply unit (20) supplies the amount of fuel determined by the fuel distribution unit to the cylinders of the internal combustion engine (10),

   characterised in that

   - the determination unit (24) is designed to:

   - determine the voltage deviation for each cylinder in relation to the voltage signals of the neighbouring cylinders relative to the ignition sequence and

   - correct the amount injected in dependence on the voltage deviation.

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