Method for operating an internal combustion engine

Abstract

Methods comprising: arranging a binary lambda sensor and a second sensor downstream of a catalytic converter; when the engine is run for the first time, using an initial lambda setpoint for closed-loop control; measuring the NH.sub.3 value in the exhaust gas; simultaneously measuring the signal from the binary lambda sensor; if the NH.sub.3 value lies above a first threshold value, reducing the lambda setpoint value of the binary lambda signal until the NH.sub.3 value lies below the first threshold value or the binary sensor signal lies below a second threshold value; recording the corresponding binary sensor signal when the NH.sub.3 value passes the first threshold value, for binary sensor signal setpoint value adaptation, as V.sub.binary-left; and calculating the real lambda setpoint value.

Claims

1. A method for operating an internal combustion engine, with a 3-way catalytic converter with closed-loop lambda control, the method comprising: arranging a binary lambda sensor and a second sensor downstream of the 3-way catalytic converter, wherein the second sensor comprises at least one of an NO.sub.x and/or a NH.sub.3 sensor; when the internal combustion engine is run for a first time, setting a lambda setpoint value for the closed-loop control using the binary lambda sensor to an initial value; during the closed-loop lambda control with the setpoint value, measuring an NH.sub.3 value in the exhaust gas downstream of the 3-way catalytic converter by means of a NO.sub.x signal or a NH.sub.3 signal from the NO.sub.x and/or NH.sub.3 sensor at a first time; measuring the signal from the binary lambda sensor at the first time; if the NH.sub.3 value lies above a first threshold value, reducing the lambda setpoint value of the binary lambda signal until the NH.sub.3 value lies below the first threshold value or the binary lambda signal lies below a second threshold value; recording the corresponding binary sensor signal when the NH.sub.3 value passes the first threshold value, for a binary sensor signal setpoint value adaptation, as V.sub.binary-left; and calculating a real lambda setpoint value for the closed-loop lambda control using:
V.sub.binary setpoint value=a×V.sub.binary-left+(1−a)×V.sub.binary-right  (1) where V.sub.binary-left=a binary sensor signal at a NH.sub.3 limit in a rich direction for setpoint value adaptation V.sub.binary-right=a binary sensor signal closer to a lambda of 1 on a rich side a=a weighting factor between 0 and 1.

2. The method as claimed in claim 1, further comprising, every time the NH.sub.3 signal passes the first NH.sub.3 threshold value during operation of the internal combustion engine, recording the corresponding binary sensor signal again and performing a new setpoint value calculation in accordance with equation (1).

3. A method for operating an internal combustion engine with a 3-way catalytic converter with closed-loop lambda control, the method comprising: arranging a linear lambda sensor and a second sensor downstream of the 3-way catalytic converter, wherein the second sensor comprises at least one of a NO.sub.x and/or a NH.sub.3 sensor; when the internal combustion engine is run for a first time, setting a lambda setpoint value for the closed-loop control using the linear lambda sensor to an initial value; during the closed-loop lambda control with the initial value, measuring a NH.sub.3 value in exhaust gas downstream of the 3-way catalytic converter using a signal from the second sensor at a first time; measuring a binary sensor signal and a linear sensor signal from the linear lambda sensor at the first time; if the NH.sub.3 value lies above a first threshold value, increasing the lambda setpoint value of the linear lambda sensor signal until the NH.sub.3 value lies below the first threshold value or the binary sensor signal lies below a second threshold value; recording a corresponding linear lambda sensor signal when the NH.sub.3 value passes the first threshold value, fora linear lambda setpoint value adaptation, as Lambda.sub.left; if, initially, the binary sensor signal lies below the second threshold value, reducing the lambda setpoint value of the linear lambda sensor signal until the binary lambda signal lies above the second threshold value or a NH.sub.3 signal lies above the first threshold value; recording the corresponding linear lambda sensor signal when the binary sensor signal passes the second threshold value, for the linear lambda setpoint value adaptation, as Lambda.sub.right; and calculating a real lambda setpoint value in accordance with the following equation:
Lambda.sub.setpoint value=a×Lambda.sub.left+(1−a)×Lambda.sub.right  (2) where Lambda.sub.left=linear lambda sensor signal at a NH.sub.3 limit in a rich direction for the setpoint value adaptation, Lambda.sub.right=linear lambda signal closer to a lambda of 1 on a rich side in a case of the binary sensor signal at the second threshold value, a=a weighting factor between 0 and 1.

4. The method as claimed in claim 3, further comprising, every time the NH.sub.3 signal passes the first threshold value during the operation of the internal combustion engine or the binary sensor signal passes the second threshold value, recording a corresponding linear lambda sensor signal as Lambda.sub.left or Lambda.sub.right and using the sensor signal as a new setpoint value calculation in accordance with equation (2).

5. The method as claimed in claim 3, wherein, for an on-board diagnosis, the NO.sub.x sensor signal at the lambda setpoint value is used for closed-loop control either with the binary sensor signal or with the linear lambda sensor signal.

6. The method as claimed in claim 5, wherein, if a value obtained in accordance with claim 5 lies above a third threshold value, the 3-way catalytic converter is classified as faulty.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The teachings herein are explained in detail below with reference to an exemplary embodiment in conjunction with the drawing. The single FIGURE shows, in a diagram, the NO.sub.x and binary and linear lambda signals from a NO.sub.x sensor with an integrated lambda probe.

DETAILED DESCRIPTION

(2) In some embodiments, there are separate sensors to be provided as the binary lambda sensor and NO.sub.x and/or NH.sub.3 sensor. Rather, use may for example also be made of a NO.sub.x or NH.sub.3 sensor with an integrated lambda probe. The weighting factor a used in equation (1) above, which lies between 0 and 1, may be selected as a function of the air mass flow. In most cases, this weighting factor is selected to be between 0.5 and 0.9. In the case of a large air mass flow, the weighting factor lies closer to 0.9 in order to prevent a NO.sub.x breakthrough.

(3) In some embodiments, the closed-loop lambda control can be performed particularly quickly and precisely. Compliance with the desired emissions limits can be ensured over the service life of the internal combustion engine under varying conditions and even with an aged 3-way catalytic converter, with particularly low outlay in terms of calibration.

(4) In some embodiments, the method according to the invention is furthermore distinguished by the fact that, every time the NH.sub.3 signal passes the NH.sub.3 threshold value (first threshold value) again during the operation of the internal combustion engine, the corresponding binary sensor signal is recorded again and used for a new setpoint value calculation in accordance with equation (1).

(5) In some embodiments, the methods can be used for the setpoint value calculation of a linear lambda sensor signal downstream of the 3-way catalytic converter. Here, in order to achieve the abovementioned object, the teachings herein provides a method for operating an internal combustion engine, in the exhaust-gas tract of which a 3-way catalytic converter with closed-loop lambda control is arranged, which method comprises the following steps: arranging a linear lambda sensor and a NO.sub.x and/or NH.sub.3 sensor downstream of the 3-way catalytic converter; when the internal combustion engine is run for the first time, setting a lambda setpoint value for the control by means of the linear lambda sensor to an initial value; during the closed-loop lambda control with this setpoint value, measuring the NH.sub.3 value in the exhaust gas downstream of the 3-way catalytic converter by means of a NO.sub.x signal or NH.sub.3 signal from the NO.sub.x and/or NH.sub.3 sensor; simultaneously measuring a binary sensor signal and a linear sensor signal from the linear lambda sensor; if the NH.sub.3 value lies above a first threshold value, increasing the lambda setpoint value of the linear lambda sensor signal until the NH.sub.3 value lies below the first threshold value or the binary sensor signal lies below a second threshold value; recording the corresponding linear lambda sensor signal when the NH.sub.3 value passes the first threshold value, for linear lambda setpoint value adaptation, as Lambda.sub.left; if, initially, the binary sensor signal lies below a second threshold value, reducing the lambda setpoint value of the linear lambda sensor signal until the binary lambda signal lies above the second threshold value or the NH.sub.3 signal lies above the first threshold value; recording the corresponding linear lambda sensor signal when the binary sensor signal passes the second threshold value, for linear lambda setpoint value adaptation, as Lambda.sub.right; and calculating the real lambda setpoint value in accordance with the following equation:
Lambda.sub.setpoint value=a×Lambda.sub.left+(1−a)×Lambda.sub.right  (2)

(6) where

(7) Lambda.sub.left=linear lambda sensor signal at the NH.sub.3 limit in the rich direction for setpoint value adaptation,

(8) Lambda.sub.right=linear lambda signal closer to lambda 1 on the rich side in the case of a binary sensor signal at the 2nd threshold value,

(9) a=weighting factor between 0 and 1.

(10) It is not necessary for separate sensors to be provided as the linear lambda sensor and NO.sub.x and/or NH.sub.3 sensor. Rather, use may for example also be made of a NO.sub.x or NH.sub.3 sensor with an integrated lambda probe. The weighting factor a specified above may be selected as a function of the air mass flow. In most cases, the weighting factor is selected to be between 0.4 and 0.8. In the case of a large air mass flow, the weighting factor lies closer to 0.8 in order to prevent a NO.sub.x breakthrough.

(11) In some embodiments, every time the NH.sub.3 signal passes the NH.sub.3 threshold value (first threshold value) during the operation of the internal combustion engine or the binary sensor signal passes the second threshold value, the corresponding linear lambda sensor signal is recorded again as Lambda.sub.left or Lambda.sub.right and used for a new setpoint value calculation in accordance with equation (2).

(12) In some embodiments, the initial value of the lambda setpoint value is preferably 750 mV. The first threshold value (NH.sub.3 value) is preferably 10 ppm, while the 2nd threshold value (binary sensor signal) is preferably 650 mV.

(13) In some embodiments, the initial value of the lambda setpoint value is preferably 0.997. The first threshold value (NH.sub.3 value) is preferably 10 ppm, while the second threshold value (binary signal) is preferably 650 mV.

(14) In some embodiments, for on-board diagnosis, the NO.sub.x sensor signal at the lambda setpoint value is used for closed-loop control either with the binary sensor signal or with the linear lambda sensor signal. Here, if the correspondingly obtained value is above a third threshold value, the 3-way catalytic converter is classified as defective.

(15) As discussed above, the teachings herein describe the adaptation of the binary sensor signal or linear lambda sensor signal downstream of the 3-way catalytic converter on the rich side (lambda<1) by means of a NO.sub.x or NH.sub.3 sensor signal of the NO.sub.x and/or NH.sub.3 sensor with subsequent determination of the lambda setpoint value either in the form of the binary sensor signal or lambda signal on the basis of the adapted signal for precise closed-loop lambda control downstream of the 3-way catalytic converter.

(16) The FIGURE shows the linear lambda sensor signal downstream of the 3-way catalytic converter on the abscissa and the NO.sub.x signal and the binary sensor signal on the ordinate. In the above-described first method variant, the lambda setpoint value for closed-loop control with the binary lambda sensor downstream of the 3-way catalytic converter is set at an initial value of 750 mV. As described above, the NH.sub.3 value downstream of the 3-way catalytic converter and the corresponding binary signal are then measured during the closed-loop lambda control with this setpoint value. If, here, the NH.sub.3 value lies above 10 ppm, the lambda setpoint value of the binary sensor signal is reduced until the NH.sub.3 value lies below 10 ppm or the binary sensor signal lies below 650 mV (second threshold value). The corresponding binary sensor signal when NH.sub.3 passes the corresponding threshold value is recorded as V.sub.binary-left.

(17) Furthermore, the value V.sub.binary-right is acquired, which corresponds to the binary sensor signal closer to lambda on the rich side and which in this case is 650 mV. Then, from the equation given above, the corresponding binary setpoint value (V.sub.binary setpoint value) is calculated with the aid of a weighting factor.

(18) In some embodiments, the lambda setpoint value for closed-loop control with a linear lambda sensor downstream of the 3-way catalytic converter is set at an initial value of 0.997. The individual method steps are then carried out in the manner described above, wherein, here, a value of 10 ppm is taken as a basis as the first threshold value (NH.sub.3 value) and a value of 650 mV is taken as a basis as the second threshold value (binary signal). The corresponding values Lambda.sub.left and Lambda.sub.right are ascertained in the manner described above. The lambda setpoint is calculated from equation (2) with the aid of the corresponding weighting factor.