DE10250219A1 - Regulator and method for regulating a NOx sensor arranged in an exhaust gas duct of an internal combustion engine - Google Patents

Abstract

The invention relates to a method and a controller for operating an exhaust gas sensor arranged in an exhaust gas duct of an internal combustion engine. DOLLAR A It is provided that the operating parameters of the exhaust gas sensor are regulated by a model-based controller and / or the exhaust gas flow-dependent pre-control of operating parameters of the exhaust gas sensor.

Description

The invention relates to a method and a controller for operating one in an exhaust gas duct of an internal combustion engine arranged exhaust gas sensor with the in the preamble of claims 1 and 19 mentioned characteristics.

It is known that, for example, NO _x sensors are usually used to determine the NO _x content in the exhaust gas of an internal combustion engine. Such NO _x sensors are known in various designs, so that a detailed description can be dispensed with here. Especially with a lean executable combustion engine, it is to comply with the NO _x limit important to the NO _x content in the exhaust system behind a NO _x trap to know in order to, for example, determine the time at which _x is a storage of NO in the NO _x storage is no longer possible, that is, the NO _x storage is filled, so that a regeneration phase is necessary.

For this purpose, there is usually a measuring device behind the catalytic converter in the exhaust tract of an at least temporarily lean-burn internal combustion engine, which is capable of measuring the NO _x concentration in the exhaust gas, for example a NO _x sensor. The measurement accuracy of exhaust gas sensors such as NO _x sensors or lambda sensors generally depends on external parameters. It is therefore important to keep these parameters in the areas that are optimal for precise control and to adjust them if necessary. In the case of NO _x sensors, for example, the temperature must be kept constant in order to ensure a high accuracy of the signal. The smaller the deviations from the target temperature of the sensor, the more accurate the sensor signal.

So far this exhaust gas sensor for the Temperature control a PI controller based on voltage without pre-control depending on the exhaust gas mass flow used, which with a resistance difference as a controller input variable and Voltage works as controller output variable. The weak point of this system is the great inaccuracy in the regulation the sensor temperature due to fluctuations in the exhaust gas mass flow due to among other things, a missing model of the route to be controlled.

The invention is therefore the object based on a regulator and a method for regulating one in one Exhaust gas duct of an internal combustion engine arranged exhaust gas sensor to create, which solve the disadvantages mentioned, and in particular a robust controller or a robust method for Provide control of an exhaust gas sensor.

This task is done by a controller and a method with the features mentioned in claims 1 and 19 solved.

A particular advantage of the process for operating an in an exhaust duct of an internal combustion engine arranged exhaust gas sensor is that the measurement accuracy of exhaust gas sensors increased is by regulating the operating parameters of the exhaust gas sensor through a model-based controller and / or an exhaust gas flow-dependent pilot control of operating parameters of the exhaust gas sensor.

For regulating operating parameters one arranged in an exhaust duct of an internal combustion engine Exhaust gas sensor is therefore used a controller, which is thereby distinguishes that the controller is designed as a model-based controller and has a structure predetermined by a model of the controlled system.

In a preferred embodiment of the method according to the invention it is provided that the operating parameter temperature is regulated and / or controlled when operating a NO _x sensor. It is advantageous if the temperature is determined by measuring an electrical resistance value. It is also advantageous if the control system evaluates the difference between the current and the target temperature of the sensor as a controller input variable and the heating power for heating the sensor varies as a controller output variable. This creates a linear relationship between controller input and output variables.

In a preferred embodiment of the method according to the invention it is provided that the exhaust gas flow-dependent precontrol is set up in this way is that the exhaust gas flow dependent Pre-control active when the exhaust gas flow decreases or increases very quickly becomes. In particular, this can be achieved in that the exhaust gas flow-dependent pilot control becomes active when the exhaust gas flow is faster than the sampling time coordinated gradient changes.

In a further preferred embodiment The invention provides that in the release condition emission current dependent Feedforward control of the current value of the measured sensor resistance and / or the current value of the measured sensor temperature is taken into account.

It proves to be an advantage if with rapidly falling exhaust gas mass flow, the pilot control with for a short time a reduced heating output and a rapidly increasing exhaust gas mass flow the pilot control reacts briefly with an increased heating output. This will be an undesirable one heating or cooling of the sensor compensated.

In a further preferred embodiment of the method according to the invention, it is provided that, when the exhaust gas sensor is precontrolled, several successive differences in the measured exhaust gas mass flow values are evaluated. You get good results, if the number of temporally successive differences in the measured exhaust gas mass flow values to be evaluated for a pilot control is determined as a function of the sampling time, with a higher number being evaluated for short sampling times and a smaller number for long sampling times.

It has also proven to be beneficial that a feedforward control tuned to a sampling time of 50 ms with a low heat output value becomes active if three in time successive differences in the measured exhaust gas mass flow values larger than are the gradient to be applied. Whereas one for a sampling time Pre-control coordinated with 50 ms with a high heating output value advantageously becomes active when four consecutive times Differences in the measured exhaust gas mass flow values are smaller than that gradient to be applied. These two approaches pose each represents a compromise between avoiding incorrect control and a short response time.

In order to prevent undesired cooling of the exhaust gas sensor, sees a preferred embodiment of the method according to the invention before that at least at the beginning of overrun phases a high heating output pilot control he follows.

It proves to be advantageous that the model-based controller using a linear continuous time Procedure is determined. It has proven to be particularly practical highlighted when the model-based controller using the LQG / LTR process (LQG / LTR = Linear Quadratic Gaussian / Loop Transfer Recovery).

A particularly robust controller can be obtained if the model of the controlled system is based on the parameters time constant T, damping d and static gain k _SR .

In a further preferred embodiment of the method according to the invention it is provided that the difference equation on which a time-discrete implementation is based hnoCy = k SR · (HNO0U · hno0u + HNO1U · hno1u + HNO2U · hnoiu) - ((–HNO1YK) · hno1y + (–HNO2YK) · hno2y) is where

hno0y the current output variable, hno1y the output variable calculated in the previous time cycle, hno2y the two output cycles previously calculated, hno0u the current input variable, hno1u the input variable measured in the previous time cycle, hno2u the input variable measured two times before, KSR the static gain and HNOij the control parameters (i = 0, 1, 2 and j = U, YK) represent.

Has proven to be particularly advantageous if the controller is designed as a linear controller. At the Using a linear controller gives good control results, if the controlled system also has a linear relationship, this means, if between controller input and controller outputs linear relationship exists.

A preferred embodiment of the controller according to the invention is characterized in that the controller has a Kalman filter and includes optimal state feedback. To avoid undesired "run-up" of the integrator it is advantageous if the controller uses an integrator windup avoiding integrator.

In a further preferred embodiment of the controller according to the invention it is provided that the controller is a means for measuring the exhaust gas mass flow value comprises, whereby an exhaust gas-dependent feedforward control is made possible.

Further preferred configurations the invention result from the remaining, mentioned in the subclaims Features.

The invention is explained in more detail below in exemplary embodiments with reference to the associated drawings. As an example, a NO _x sensor is used as the exhaust gas sensor. Show it:

1 a representation of the characteristics determined in a jump test and

2 a representation of the amplitude and phase response (Bode diagram) of the open chain consisting of the controller according to the invention and an integrator avoiding an integrator windup.

The controller according to the invention is distinguished by the fact that it is based on a new controller structure which contains a model of the controlled system. Due to this additional information about the controlled system, a higher control accuracy is achieved. In addition to the new controller, the relationship between controller input and output variables has been linearized in order to achieve better control results. The controller now varies the heating power and thus regulates the heating of the sensor to its target temperature. Controller input variable is a temperature difference that results from the current and the target temperature of the sensor. The new controller structure includes a special integrator, the advantage of which is the avoidance of an "integrator windup", that is, an undesired "run-up" of the integrator when the manipulated variable has reached the saturation value of the controlled system input. In addition, the new controller structure can be combined with a pre-control depending on the exhaust gas mass flow in order to compensate for the dead time due to the position of the NO _x sensor far behind in the exhaust tract.

An exemplary embodiment of the model-based controller was designed according to the LQG / LTR method (LQG / LTR = Linear Quadratic Gaussian / Loop Transfer Recovery). The LQG / LTR process is a linear, continuous design process. The exemplary controller designed with this consists of a Kalman filter as an observer and an optimal state feedback. The underlying difference equation for a time-discrete implementation, such as is implemented in the software of an engine control unit, is: hnoCy = k SR · (HNO0U · hno0u + HNO1U · hno1u + HNO2U · hnoiu) - ((–HNO1YK) · hno1y + (–HNO2YK) · hno2y) with the sizes defined above.

Since the order of the controlled system model specifies the order of the model-based controller, it was necessary to determine a suitable, yet simple model of the controlled system. For this purpose, jump tests were carried out on the route, with jumps in performance being made on the route in such a way that the route output size, the sensor temperature, jumps around its working point, the setpoint temperature, as would be expected in normal operation. In 1 the result of a jump test carried out is shown. The voltage jump size 10 U_sprung, is converted into a power variable via the heating resistor. The intermediate size 11 R _PVS is the internal resistance of the sensor and the desired step response 12 T_Tip, the temperature of the sensor element, are also plotted in the diagram. The measured step response was measured using a suitable aid 12 the simulated behavior of a PT ₂ element 13 T_model overlaid. As in 1 good to see, it turned out that a PT ₂ element approximates the measured behavior well. The parameters of the exemplary model are: time constant T = 4.2s, damping d = 1.2s and static gain k _SR = 17 ° C / W.

2 shows the amplitude and phase response (Bode diagram) of the open chain 20 consisting of the controller according to the invention and the special integrator described above. With a phase reserve of around 73 °, the structure is extremely robust.

mit der Temperaturerhöhung ΔT in [K] und der Masse m in [kg] des Körpers sowie der ihm zugeführten Wärmemenge Q in [Ws]. Die Umrechnung vom bisher verwendeten Innenwiderstandswert des Sensors in seine Temperatur erfolgt mit Hilfe einer vom Sensorhersteller ermittelten nichtlinearen Kennlinie.Since it is a linear controller, a linear relationship between controller input and output variable is required for a good control result. This is the reason for the change in the controller input variable from the measured sensor resistance value to a sensor temperature value and from the heating voltage value of the controller output variable to a heating output value. The linear relationship between the temperature increase of a body and the amount of heat supplied to it is:

with the temperature increase ΔT in [K] and the mass m in [kg] of the body and the amount of heat Q supplied to it in [Ws]. The conversion of the internal resistance value of the sensor used to its temperature is carried out with the help of a non-linear characteristic curve determined by the sensor manufacturer.

In order to better take fluctuations in the exhaust gas mass flow into account when regulating the temperature of the NO _x sensor, the proposed new controller structure can be combined with a pilot control dependent on the exhaust gas mass flow. The pilot control becomes active when the exhaust gas mass flow increases or decreases very quickly. The idea behind this is that the exhaust gas mass flow provides information about a provisional cooling or heating of the sensor located further back in the exhaust tract. If the mass flow changes faster than the gradients matched to the sampling time, the pilot control becomes active by either a strong heating up to anticipate the upcoming cooling down, or a lowering of the heating power to a low value due to an upcoming heating up. The current value of the measured sensor resistance is included in the enabling condition of the pilot control in order to avoid that the heating power pilot control is too low when the sensor temperature is too low and vice versa. As an alternative to the sensor resistance, the sensor temperature can also be measured, the temperature and resistance reversing into one another on the basis of the characteristic curve mentioned above be counted.

It is established through measurements that with rapidly falling exhaust gas mass flow at first an undesirable increase of the sensor temperature to which the pilot control is briefly compensating with a reduced heating output value. Conversely, with a rapidly increasing exhaust gas mass flow in the first Wait a minute of the sensor, on which the pilot control in turn is briefly with an increased Heating output reacts.

The measurement of the exhaust gas mass flow is affected by measurement noise. To get away from this To delimit measurement noise, it is usually not appropriate on every (small) change of the exhaust gas mass flow to react with an adjustment of the heating power. Instead, it will make sense depending on the sampling time a higher one or less number of successive differences of the measured exhaust gas mass flow values for feedforward control. The number of consecutive differences must be taken into account so chosen that a compromise is found between the demarcation against the measurement noise and a too long reaction time. For shorter sampling times it may be advantageous to consider the number of consecutive times increase the following differences in the measured exhaust gas mass flow values; at longer Sampling times may need to be reduced.

For a pilot control with a low heating output value and the special, exemplary sampling time of 50 ms, for example the criterion "three successive differences in the measured exhaust gas mass flow values are bigger than the gradient to be applied (corresponds to a reaction time of 3 * 50ms) "a compromise represent between avoiding an incorrect feedforward control and a short response time.

For a feedforward control with a high heating power value, the compromise can be made in a special embodiment with the sampling time 50 ms are formed, for example, by the criterion "four consecutive differences in the measured exhaust gas mass flow values are smaller than the gradient to be applied (corresponds to a reaction time of 4 * 50ms)".

At the beginning of a fuel cut-off phase cools the Sensor usually something out of. Therefore also for Overrun phases already over the pilot control can be switched to maximum heating, even before using the Control deviation and the controller itself this is the case.

The invention is not limited to the embodiments shown here. Rather, it is possible by combining and modifying the means and features mentioned further versions to realize without leaving the scope of the invention.

10

Voltage step size

11

between size

12

Step response

13

simulated behavior of a PT ₂ link

20

open Chain

Claims (24)

Method for operating an exhaust gas sensor arranged in an exhaust gas duct of an internal combustion engine, characterized in that operating parameters of the exhaust gas sensor are regulated by a model-based controller and / or pre-control of operating parameters of the exhaust gas sensor depending on the exhaust gas flow. A method according to claim 1, characterized in that the operating parameter temperature is regulated and / or controlled when operating a NO _x sensor. A method according to claim 2, characterized in that temperature by measuring an electrical resistance value is determined. A method according to claim 2, characterized in that the control is the difference between the current and the target temperature evaluates the sensor as a controller input variable and the heating power for heating the sensor as a controller output variable varies. Method according to one of the preceding claims, characterized characterized that the exhaust gas flow-dependent precontrol at very rapidly increasing or decreasing exhaust gas flow becomes active. Method according to one of the preceding claims, characterized characterized in that the exhaust gas flow-dependent precontrol becomes active, when the exhaust gas flow changes faster than gradients matched to the sampling time. Method according to one of the preceding claims, characterized characterized that in a release condition of the exhaust gas flow-dependent precontrol - the current Value of the measured sensor resistance and / or - the current Value of the measured sensor temperature is taken into account. Method according to one of the preceding claims, characterized characterized in that with rapidly falling exhaust gas mass flow Feedforward control reacts briefly with a reduced heating output. Method according to one of the preceding claims, characterized characterized in that with a rapidly increasing exhaust gas mass flow Pilot control reacts briefly with an increased heating output. Method according to one of the preceding claims, characterized characterized in that when the exhaust gas sensor is precontrolled successive differences in the measured exhaust gas mass flow values be evaluated. Method according to one of the preceding claims, characterized characterized that the number of to be evaluated for a feedforward control successive differences in the measured exhaust gas mass flow values dependent on the sampling time is determined, with a short sampling time higher number, with long sampling times, a smaller number of differences are evaluated becomes. Method according to one of the preceding claims, characterized characterized that a tuned to a sampling time of 50 ms Feedforward control with a low heating output value becomes active if three consecutive differences in the measured exhaust gas mass flow values larger than are the gradient to be applied. Method according to one of the preceding claims, characterized characterized that a tuned to a sampling time of 50 ms Feedforward control with a high heating output value becomes active if four successive differences in the measured exhaust gas mass flow values are smaller than the gradient to be applied. Method according to one of the preceding claims, characterized characterized in that at least at the beginning of overrun phases a high Heating power precontrol takes place. Method according to one of the preceding claims, characterized characterized that the model-based controller using a linear time continuous process is designed. Method according to one of the preceding claims, characterized characterized that the model-based controller using the LQG / LTR process (LQG / LTR = Linear Quadratic Gaussian / Loop Transfer Recovery) becomes. Method according to one of the preceding claims, characterized in that the model of the controlled system is based on the parameters - time constant (T), - damping (d (and - static gain (k _{S R} ). Method according to one of the preceding claims, characterized in that the difference equation on which a time-discrete implementation is based hnoCy = k _SR · (HNO0U · hno0u + HNO1U · hno1u + HNO2U · hnoiu) - ((–HNO1YK) · hno1y + (–HNO2YK) · hno2y) is where hno0y the current output variable, hno1y the output variable calculated in the previous time cycle, hno2y the two output cycles previously calculated, hno0u the current input variable, hno1u the input variable measured in the previous time cycle, hno2u the input variable measured two times before, k _SR the static gain and NNOij the control parameters (i = 0, 1, 2 and j = U, YK) represent. Regulator for regulating operating parameters of a arranged in an exhaust duct of an internal combustion engine Exhaust gas sensor, characterized in that the controller as a model-based Controller is designed and a model of the controlled system has a predetermined structure. Controller according to claim 19, characterized in that the controller is designed as a linear controller. Controller according to one of claims 19 or 20, characterized in that that between controller input and controller outputs linear relationship exists. Controller according to one of claims 19 to 21, characterized in that that the controller includes a Kalman filter and optimal state feedback. Controller according to one of claims 19 to 22, characterized in that that the controller is an integrator avoiding an integrator windup having. Controller according to one of claims 19 to 23, characterized in that that the controller is a means of measuring the exhaust gas mass flow value includes.