WO2007031365A1 - Method and device for determining the gas components in the exhaust gas of an internal combustion engine - Google Patents

Abstract

In a method for determining gas components in the exhaust gas of an internal combustion engine, the concentration of individual gas components in the exhaust gas, in particular of at least one gas component other than oxygen, is determined from the signal of a broadband probe which is arranged in the exhaust gas stream, and the signal of a jump probe which is arranged in the exhaust gas stream.

Description

Method and device for determining the gas components in the exhaust gas of an internal combustion engine

State of the art

The invention relates to a method and a device for determining gas components in the exhaust gas of an internal combustion engine according to the preamble of the independent claims.

More particularly, the invention relates to a method and apparatus for determining gas components in the exhaust gas of internal combustion engines operated with an air-fuel mixture near stoichiometric equilibrium, such as gasoline engines in vehicles. Such vehicles with internal combustion engines, which meet today's emissions regulations, especially in Europe or in the United States of America, have an exhaust system with at least one catalyst and two or more exhaust probes for determining the air-fuel ratio, or correlated with the air ratio lambda. In a typical arrangement, immediately downstream of the exhaust manifold a first exhaust gas probe, the so-called "control probe", downstream of this one (three-way) catalyst and downstream of the catalyst another exhaust gas probe, the so-called "guide probe" arranged.

On the control probe builds up a fast lambda control to compensate for large pilot error of the mixture composition. The guide probe is used for a superimposed second control loop, the so-called control loop, which tion of scattering of the control probe and the optimization of the mixture composition with a view to reducing emissions.

There are now several types of exhaust probes known. Such exhaust gas sensors are described for example in the textbook "BOSCH Rraftfahrtechnisches Taschenbuch", Vieweg Verlag, 25th edition, 2003, pages 133, 134. The lambda probes described therein provide a measure of the air ratio lambda in the exhaust gas of combustion processes. The mode of operation of the lambda probes described is based on the principle of a galvanic oxygen concentration cell with a solid electrolyte. The surfaces are provided with electrodes made of a gas-permeable platinum layer. Due to the catalytic activity of the platinum, the exhaust gas is set in equilibrium by post-combustion, so that the oxygen equilibrium partial pressure is established.

There are now essentially two types of exhaust probes, namely jump probes and broadband probes used today. The jump probe represents an oxygen concentration sensor and works on the Nernst principle. Here, the potential difference across an electrolyte is measured, which is exposed to the exhaust gas on one side and a reference gas (air) on the other side. For this purpose, electrodes are applied to the electrolyte on both sides. The potential difference is output as a probe signal. The probe characteristic, that is to say the curve of the probe signal above the air ratio lambda, drops sharply at lambda = 1. For this reason, such a probe is also referred to as a jump probe.

A broadband probe has a multilayer ceramic. It consists essentially of a combination of a Nernst probe, that is, of a concentration probe acting as a galvanic cell, as well as a limiting current or pumping cell. About the Nernst cell, also referred to as a sensor cell, as in the lambda probe, the potential difference between the exhaust gas and a reference gas is measured. To the pumping cell, which is basically of the same kind as the concentration cell known per se, a voltage is applied from the outside. This generates a current called pumping current, with which - depending on polarity - oxygen ions are transported. An electronic control circuit causes the pumping cell to always add or remove just as much oxygen from the exhaust gas volume which is in contact with the sensor cell, that in the exhaust gas volume. Lumen the state lambda = 1 sets, wherein in the lean range, that is, in excess air, oxygen is pumped, whereas in the rich range, that is, in excess fuel, oxygen is supplied. The pumping current set by the control circuit depends on the air ratio lambda in the exhaust gas. It forms the output signal of the broadband probe. The structure of the jump probe and the broadband probe and its sensor signals are from the textbook "BOSCH Automotive Paperback", Vieweg- Verlag, 25th Edition, 2003, pages 133, 134, to which reference is made here, out.

As control probe either a jump probe or a broadband probe is used. As guide probes usually jump probes are used.

Although the signal of both types of probe depends primarily on the lambda value of the exhaust gas, but it is also influenced by a different exhaust gas composition at the same lambda, this influence is different for the two types of probes. This influence is based on so-called cross sensitivity to certain exhaust gas components. The ratio between carbon monoxide (CO) and hydrogen (H ₂ ), for example, has an effect especially in the rich range. In the raw exhaust gases this ratio remains largely constant. However, downstream of a catalyst, it may vary depending on the catalyst coating, catalyst aging and operating point. This leads to an adverse effect on the lambda probe signal.

The invention is therefore based on the object of specifying a method and an apparatus for determining gas components in the exhaust gas of an internal combustion engine, which not only the detection of the air ratio lambda, but also the determination of carbon monoxide (CO) concentration and the hydrogen (H ₂₎ Allow concentration.

Advantages and illustration of the invention This object is solved by the features of the independent claims. Advantageous embodiments and further developments are the subject of the dependent claims in each case dependent claims.

The invention takes advantage of the different cross sensitivities of the two types of probes, so as to measure not only the air ratio lambda, but also the specific concentrations of oxygen (O ₂ ), carbon monoxide (CO) and hydrogen (H ₂ ) in the exhaust gas downstream of a catalyst. For this purpose, the concentration of the individual gas components of the exhaust gas is determined from the signal of a jump probe arranged downstream of the catalytic converter and from the simultaneously detected signal of a broadband probe arranged in the immediate vicinity of the jump probe in the exhaust gas.

For this purpose, the dependence of the signal of the jumping probe on the concentration of carbon monoxide (CO) and the concentration of hydrogen (H ₂ ) and on the dependence of the signal of the broadband probe on the concentration of carbon monoxide (CO) and on the concentration of hydrogen is preferred (H ₂ ) on the concentration of carbon monoxide (CO) and hydrogen (H ₂ ) closed. The knowledge of these concentrations can be used for several purposes. On the one hand, the knowledge for the compensation of the described transverse sensitivities and thus for the more accurate determination of the air ratio lambda is advantageous. This can improve the management control. In addition, from the knowledge of the concentration of the individual gas components, a determination of the aging state of the catalyst, in particular for the purpose of on-board diagnosis, take place. Finally, the knowledge of the concentration of the gas components is also advantageous for a correction of a catalyst model in a model-based mixture control known per se.

drawing

Further advantages and features of the invention are the subject of the following description and the drawings of an embodiment of the invention. In the drawing show:

Fig. 1 shows an inventive device for determining the gas components in the exhaust gas of an internal combustion engine and

Fig. 2a shows the dependence of a jump probe of the CO and H ₂ concentration

2b shows the dependence of a broadband probe on the CO and H ₂ -

Concentration.

Description of exemplary embodiments

In the exhaust gas line 105 of an internal combustion engine 100, a first exhaust gas probe 110, whose output signal is fed to a control device 200, is arranged immediately downstream of the exhaust manifold (not shown). This exhaust gas probe 110 serves as a so-called control probe. Based on its signal, a fast lambda control takes place to compensate for large pilot control errors in the mixture composition.

On the control probe 110 is followed by a (three-way) catalyst 120. Downstream of the catalyst 120, a further jump probe 130 and a broadband probe 140, which is disposed in close proximity to the other jump probe 130 in the exhaust gas is provided. The output signals of the further jump probe 130 and the broadband probe 140 are also supplied to the control device 200.

Downstream of the catalyst 120 occur in rich operation practically only reducing, in lean operation practically only oxidizing exhaust gas components, that is on the one hand oxygen (O ₂ ) (reducing exhaust gas constituent) and on the other hand carbon monoxide (CO) and hydrogen (H ₂ ) (oxidizing exhaust gas constituents). In other words, reducing and oxidizing gas components do not occur simultaneously in the exhaust gas. For this reason, in the lean region, the signal of the broadband probe 140 can be used to determine the oxygen (O ₂ ) concentration, and in this way the air ratio lambda can be determined.

In contrast, the carbon monoxide (CO) and the hydrogen (H ₂ ) concentration must be determined simultaneously in the rich range. For this purpose, those shown in Fig. 2a, 2b are shown Dependencies of the probe signals of the jump probe 130 and the broadband probe 140 on the carbon monoxide (CO) concentration and the hydrogen (H ₂ ) concentration used. The functional relationship of the probe signal of the jump probe 130 to the carbon monoxide (CO) and hydrogen (H ₂ ) concentrations is significantly different from the functional relationship of the probe signal of the broadband probe 140 to the carbon monoxide (CO) - and the hydrogen (H ₂ ) -Concentration. The functional relationships can be stored in the control device 200, for example in the form of maps. It is also possible that the functional dependence of the probe signals on the carbon monoxide (CO) and the hydrogen (H ₂ ) - concentration are approximated and the corresponding functions are stored in the control unit 200. The sought carbon monoxide (CO) - as well as the sought hydrogen (H ₂ ) concentration is now determined in the controller 200 by inversion of these functions, so that from the two probe signals and their functional dependence on the concentrations, the concentrations can be determined.

In an advantageous embodiment, the two sensors 130, 140 are integrated on a single probe in the form of a multilayer ceramic. The basis for this is the broadband probe. This is to be supplemented by a device for measuring the voltage across the pumping cell. This voltage is the sum of, on the one hand, the Nernst voltage between the outer exhaust gas and the exhaust gas volume set to lambda = 1 and, on the other hand, a voltage proportion proportional to the pumping current. In knowledge of the ohmic resistance of the pump cell, this voltage component is calculated on the pump current. By subtracting this voltage component from the total voltage results in a signal voltage having the characteristic of a jump probe except for an offset. The calculations may be performed either in the integrated circuit implementing the electronic control circuit for adjusting lambda = 1 in the exhaust gas volume, or on a separate processor such as an engine control unit.

Alternatively, an additional electrode for measuring the Nernst voltage between the outer exhaust gas and the reference gas can be arranged on a broadband probe.

Claims

R. 309207Patent claims 1. A method for determining the gas components in the exhaust gas of an internal combustion engine, characterized in that from the signal of a arranged in the exhaust stream wideband probe (140) and the signal of a arranged in the exhaust gas jump probe (130) on the concentration of individual gas components of the exhaust gas, in particular at least one of Oxygen different gas component, is closed. 2. The method according to claim 1, characterized in that the broadband probe (140) and the jump probe (130) are arranged at the same location in the exhaust system or in close proximity to each other. 3. The method according to claim 1 or 2, characterized in that it is closed to the concentrations of carbon monoxide (CO) and hydrogen (H ₂ ). 4. The method according to claim 3, characterized in that one of the dependence of the signal of the jumping probe of the concentrations of carbon monoxide (CO) and hydrogen (H ₂ ) and from the dependence of the signal of the broadband probe (140) on the concentrations of carbon monoxide (CO) and of hydrogen (H ₂ ) on the concentration of carbon monoxide (CO) and hydrogen (H ₂ ) closes. 5. A device for determining the gas components in the exhaust gas of an internal combustion engine, characterized by a arranged in the exhaust broadband probe (140), arranged in the exhaust tract jump probe (130) and a circuit unit which the signal of the broadband probe (140) and the signal of the jump probe (130 ) recorded and evaluated at the same time. 6. The device according to claim 5, characterized in that the jump probe (130) and the broadband probe (140) are part of a single multilayer ceramic. 7. The device according to claim 5, characterized in that the broadband probe (140) and the jump probe (130) are arranged in the exhaust system so that there is no catalyst between them.