JP4703726B2 - Method and apparatus for determining gas component in exhaust gas of internal combustion engine - Google Patents

Description

  The present invention relates to a method and apparatus for determining a gas component in exhaust gas of an internal combustion engine.

  More particularly, the present invention relates to a method and apparatus for determining the gas components in an internal combustion engine, such as an in-vehicle Otto cycle engine exhaust gas, operated with an air / fuel mixture near theoretical equilibrium. Such vehicles, particularly with internal combustion engines that meet today's emission regulations in Europe or the United States, have at least one catalyst and two or more exhaust gases for determining the air / fuel ratio or the air number λ correlated therewith. -It has a sensor. In a typical apparatus, a first exhaust gas sensor, a so-called “control sensor” is arranged immediately downstream of the exhaust curved pipe, and a (three-way) catalyst is arranged behind the flow direction of the exhaust gas sensor. Other exhaust gas sensors, so-called “guide sensors” are arranged.

  Rapid λ control to compensate for large pre-control errors in the mixture composition is based on control sensors. Guide sensors are used for the upper second control loop, the so-called guide control, which compensates for variations in the control sensors and optimizes the mixture composition for emission reduction.

  Here, a plurality of exhaust gas sensor types are known. Such an exhaust gas sensor is described, for example, in the technical book “BOSCH Automotive Handbook”, published by Viewweg-Verlag, 25th edition, 2003, 133, page 134. The λ sensor described therein provides a measure for the number of air λ in the exhaust gas of an internal combustion engine. The method of operating the λ sensor is based on the principle of a galvanic oxygen concentration cell having a solid electrolyte. An electrode made of a gas permeable platinum layer is provided on the surface. Due to the catalytic activity of platinum, the exhaust gas is brought into an equilibrium state by post-combustion, thereby setting an oxygen equilibrium partial pressure.

  Here, almost two types of exhaust gas sensors are used today: jump sensors and broadband sensors. The jump sensor represents an oxygen concentration sensor and operates according to the Nernst principle. In this case, the potential difference between both sides of the electrolyte is measured, and one side of the electrolyte is exposed to the exhaust gas, and the other side is exposed to the reference gas (air). For this purpose, electrodes are mounted on both sides of the electrolyte. The potential difference is output as a sensor signal. The sensor characteristic curve, that is, the curve of the sensor signal with respect to the air number λ suddenly decreases at λ = 1. For this reason, such sensors are also called jump sensors.

  The broadband sensor has a multilayer ceramic. A broadband sensor essentially consists of a combination of a Nernst sensor, a concentration sensor operating as a galvanic cell, and a limiting current cell or pump cell. As in the lambda sensor, the potential difference between the exhaust gas and the reference gas is measured on both sides of the Nernst cell, also called the sensor cell. An external voltage is applied to a pump cell that is based on the same format as a known concentration cell. The voltage generates a current called a pump current, which transports oxygen ions as a function of polarity. The electronic control circuit always supplies and exhausts oxygen accurately to the exhaust gas volume in contact with the sensor cell so that the state λ = 1 is set in the exhaust gas volume. In this case, oxygen is exhausted in the lean range, ie, in excess of air, while oxygen is supplied in the rich range, ie, in excess of fuel. The pump current set by the control circuit is a function of the exhaust gas air number λ. The pump current forms the output signal of the broadband sensor. The structure of jump sensors and broadband sensors and their sensor signals are described in the technical book "BOSCH Automotive Handbook", Viewweg-Verlag Publishing, 25th edition, 2003, 133, 134, to which reference is made.

A jump sensor or a broadband sensor is used as the control sensor. A jump sensor is generally used as the guide sensor.
First of all, the signal for both sensor types is certainly a function of the λ value of the exhaust gas, but at the same λ, this signal is also affected by different exhaust gas compositions, in which case this effect is It is different for both sensor types. This effect is based on the so-called cross sensitivity for specific exhaust gas components. Therefore, particularly in the rich range, the ratio between carbon monoxide (CO) and hydrogen (H ₂ ) acts. In the untreated exhaust gas, this ratio remains almost constant. However, on the downstream side of the catalyst, this ratio may vary as a function of catalyst coating, catalyst degradation and operating point. This will adversely interfere with the λ sensor signal.

It is a main object of the present invention to provide a method and apparatus for determining a gas component in an exhaust gas of an internal combustion engine that enables not only the measurement of the air number λ but also the determination of carbon monoxide (CO) concentration and hydrogen (H ₂ ) concentration. It is a subject of the invention.

This problem is solved by the features of the independent claims. Advantageous forms and modifications are apparent from the respective dependent claims cited in the independent claims.
The present invention takes advantage of the different crossing sensitivities of both sensor types, whereby oxygen (O ₂ ), carbon monoxide (CO) and hydrogen (H ₂ ) in the exhaust gas downstream of the catalyst as well as the air number λ. ) Specific concentration can also be measured. For this purpose, the exhaust sensor is determined from the signal of the jump sensor arranged in the exhaust gas downstream of the catalyst and the signal simultaneously measured by the broadband sensor arranged in the exhaust gas close to the jump sensor. The concentration of the individual gas components of the gas is estimated.

To this end, from the relationship between the jump sensor signal and the carbon monoxide (CO) concentration and hydrogen (H ₂ ) concentration, the broadband sensor signal and the carbon monoxide (CO) concentration and hydrogen (H ₂ ) concentration From the relationship, it is preferable that the concentrations of carbon monoxide (CO) and hydrogen (H ₂ ) are estimated. Knowing these concentrations can be used for multiple purposes. On the other hand, knowing these concentrations is advantageous in order to compensate for the above cross sensitivity and thus for a more accurate determination of the air number λ. Thereby, guide control can be improved. By knowing the individual gas component concentrations, it is also possible to determine the deterioration state of the catalyst, especially for the purpose of on-board diagnosis. Finally, knowing the concentration of the gas component is also advantageous for the correction of the catalyst model in the mixture control with a model known per se.

  An exhaust gas sensor 110 is disposed immediately downstream of an exhaust curved pipe (not shown) in the exhaust system 105 of the internal combustion engine 100, and an output signal of the exhaust gas sensor 110 is supplied to the control device 200. This exhaust gas sensor serves as a so-called control sensor. Based on this signal, rapid λ control is performed to compensate for large pre-control errors in the mixture composition.

  The control sensor 110 is followed by a (three-way) catalyst 120. On the downstream side of the catalyst 120, another jump sensor 130 and a broadband sensor 140 disposed in the exhaust gas in the vicinity of the other jump sensor 130 are provided. The output signals of the other jump sensors 130 and the broadband sensor 140 are supplied to the control device 200 in the same manner.

On the downstream side of the catalyst 120, only the reducing exhaust gas component is actually generated in the rich operation, and only the oxidizing exhaust gas component is actually generated in the lean operation, that is, oxygen (O ₂ ) (reducing property). Exhaust gas component) and carbon monoxide (CO) and hydrogen (H ₂ ) (oxidative exhaust gas component) are generated on the other side. In other words, reducing and oxidizing gas components are not generated simultaneously in the exhaust gas. For this reason, the broadband sensor 140 signal is used to determine the oxygen (O ₂ ) concentration within the lean range, and thus the air number λ can be determined.

On the other hand, within the rich range, the carbon monoxide (CO) concentration and the hydrogen (H ₂ ) concentration must be determined simultaneously. For this purpose, the relationship between the sensor signals of the jump sensor 130 and the broadband sensor 140 and the carbon monoxide (CO) concentration and the hydrogen (H ₂ ) concentration shown in FIGS. 2a and 2b is used. The functional relationship between the sensor signal of the jump sensor 130 and the carbon monoxide (CO) concentration and hydrogen (H ₂ ) concentration is similar to the sensor signal of the broadband sensor 140, the carbon monoxide (CO) concentration, and hydrogen (H ₂ ). The functional relationship with concentration is significantly different. The functional relationship may be stored in the control device 200 in the form of a characteristic curve group, for example. The functional relationship between the sensor signal, the carbon monoxide (CO) concentration, and the hydrogen (H ₂ ) concentration may be expressed by an approximate expression, and the corresponding function may be stored in the control device 200. The resulting carbon monoxide (CO) concentration as well as the resulting hydrogen (H ₂ ) concentration is now determined in the controller 200 by a function inversion, whereby both sensor signals and these sensor signals The concentration can be determined from the functional relationship between the density and the concentration.

  In an advantageous embodiment, both sensors 130, 140 are integrated in the form of a multilayer ceramic on a single sensor. A broadband sensor is suitable as a base for this purpose. The broadband sensor is intended to supplement the voltage measurement device on both sides of the pump cell. This voltage is on the one hand the sum of the Nernst voltage between the outer exhaust gas and the exhaust gas volume set at λ = 1 and, on the other hand, the voltage portion proportional to the pump current. Knowing the ohmic resistance of the pump cell, the pump current is calculated from this voltage portion. By subtracting this voltage portion from the total voltage, a signal voltage having the characteristics of the jump sensor until the offset is obtained. This calculation may be performed in an integrated switch circuit that forms an electronic control circuit for setting λ = 1 in the exhaust gas volume, or may be performed in another processor, such as an engine controller.

  As an alternative, the broadband sensor may be provided with an additional electrode for measuring the Nernst voltage between the external exhaust gas and the reference gas.

FIG. 1 shows a determination device according to the invention for the gas components in an internal combustion engine exhaust gas. FIG. 2a shows the relationship between the jump sensor and the CO and H ₂ concentrations, and FIG. 2b shows the relationship between the broadband sensor and the CO and H ₂ concentrations.

Claims (5)

From the signal of the broadband sensor (140) located in the exhaust gas flow and the signal of the jump sensor (130) located in the exhaust gas flow, carbon monoxide (CO) and hydrogen (H ₂ ) in the rich range. ) To estimate the gas component in the exhaust gas of the internal combustion engine,
From the relationship between jump sensor signal and carbon monoxide (CO) and hydrogen (H ₂ ) concentration, and broad band sensor (140) signal and carbon monoxide (CO) and hydrogen (H ₂ ) concentration And determining the concentration of carbon monoxide (CO) and hydrogen (H ₂ ) from   The method according to claim 1, characterized in that the broadband sensor (140) and the jump sensor (130) are arranged at the same location in the exhaust system or close to each other. A broadband sensor (140) disposed in the exhaust gas, a jump sensor (130) disposed in the exhaust system, and simultaneously measuring the broadband sensor (140) signal and the jump sensor (130) signal; and An apparatus for determining the concentration of carbon monoxide (CO) and hydrogen (H ₂ ) in a rich range in an exhaust gas of an internal combustion engine characterized by a circuit unit to be evaluated,
From the relationship between the jump sensor signal and the concentrations of carbon monoxide (CO) and hydrogen (H ₂ ) and from the broadband sensor (140) signal and the concentrations of carbon monoxide (CO) and hydrogen (H ₂ ) The determination apparatus characterized by estimating the concentration of carbon monoxide (CO) and hydrogen (H ₂ ) from the relationship of   4. The determination device according to claim 3, characterized in that the jump sensor (130) and the broadband sensor (140) are part of only one multilayer ceramic.   4. The determination device according to claim 3, characterized in that the broadband sensor (140) and the jump sensor (130) are arranged in the exhaust system such that there is no catalyst between them.

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