KR102100836B1 - Method and device for regulating a system variable - Google Patents

Abstract

The present invention relates to a method for controlling system variables of a control system, wherein the control system is operated in one or more first and second operating states when the values of the system variables are different, and the system variables are used as sensors as actual values. It is detected, its dynamics change in a constant or unpredictable manner, and the control deviation is determined and provided to the controller of the control system based on the actual value and the target value of the system variable, and the controller outputs the control variable according to the control deviation . At this time, when the operating state for the preset time period is changed, the control variable is more strongly limited than after the time period has elapsed.
The invention also relates to an apparatus for carrying out the method.
When the sensor is at least temporarily slowed, overshooting of the control circuit is suppressed by the above method and apparatus.

Description

Method and device for controlling system variables {METHOD AND DEVICE FOR REGULATING A SYSTEM VARIABLE}

The present invention relates to a method for controlling system variables of a control system, wherein the control system is operated in one or more first operating states and second operating states when the values of the system variables are different, wherein the system variables are sensors as actual values. Is detected, its dynamics are changed in a constant or unpredictable manner, and control deviation is determined based on the actual and target values of these system variables and provided to the controller of the control system. Output.

Further, the present invention relates to an apparatus for controlling a system variable of a control system, wherein the control system includes one or more first operating states and second operating states in which values of the system variables are different, and the control system is an actual system variable. And a sensor for determining the value and a controller for the output of the control variable 34.

In a vehicle internal combustion engine, particularly in a diesel engine, a NO _x storage catalytic converter (NSC) is used for the purpose of reducing nitrogen oxide emissions. While this catalytic converter stores nitrogen oxides, the engine operates with excess air (lean). To maintain the storage capacity of the NO _x storage catalytic converter, nitrogen oxides that have already been stored must be removed frequently. To effect such regeneration of a NO _x storage catalytic converter, it is known to adjust the reduced exhaust gas atmosphere that converts stored nitrogen oxides to nitrogen. To this end, the internal combustion engine operates in rich mode, i.e. with a low stoichiometric air-fuel ratio of lambda <1.

Diesel engines are generally designed for continuous lean mode. As a result, special regeneration steps are provided to regenerate the provided NO _x storage catalytic converter to operate the diesel engine in rich mode. During this regeneration phase, the lambda is controlled by the lambda control circuit. At this time, the lambda before the NO _x storage catalytic converter is a control variable. The output signal of the lambda sensor placed upstream of the NO _x storage catalytic converter is the actual value and is usually provided to the lambda controller integrated in the engine control unit.

To effect regeneration of the NO _x storage catalytic converter, instead of lambda, other exhaust gas components or exhaust gas characteristics characteristic for the regeneration or for the flow of the regeneration are also measured and appropriately controlled by the corresponding exhaust gas sensor. Can be controlled by circuit.

Exhaust gas sensors provided as measurement elements, such as lambda sensors used in lambda control circuits, can be contaminated by soot particles that move together in the exhaust gas. Therefore, the response time of the exhaust gas sensor is extended. If the exhaust gas sensor slows down beyond a certain scale, this results in a significant shortage to the desired lambda value when switching on the lambda control at the beginning of regeneration. A controller designed for higher signal dynamics of the exhaust gas sensor attempts to control the target value by raising the control variable. However, the reason for this control deviation is the delayed response of the exhaust gas sensor. The controller is over-controlled so that the actual lambda of the exhaust gas is significantly below the target value. This can lead to a significant deterioration of exhaust gas emissions to the middle of individual cylinders.

Pollution of the exhaust gas sensor due to soot particles is not necessarily persistent. It can be reduced or completely eliminated by mechanical influences, such as by vibration or by thermal influences.

In order to prevent excessive control of the controller, it is known that the control deviation input into the controller continuously rises from zero to the set value at the beginning of reproduction by the ramp function.

It is also known to initialize the target value of control at the beginning of reproduction with the actual value, and then derive it to the unique target value by appropriate filtering or ramping.

In addition, various forms of restrictions are used, such as control deviation.

If the controller has an integrator, it is known to reduce the amplification of the integrator according to the control deviation.

In the above-mentioned measures to avoid undershooting of the control circuit, even if there is no sooting in the exhaust gas sensor, these measures have the disadvantage that they affect the switching-on behavior of the control and then the behavior.

The regenerative duration of the NO _x storage catalytic converter as the operating state to be adjusted is in the range of several seconds. Therefore, methods for deriving the control deviation or the target value to the target value by one ramp can only be used limitedly, otherwise the desired target value will be maintained for too long. Therefore, in this way, the failure to reach the target value cannot be sufficiently suppressed in the early stage of regeneration.

As a disadvantage when correcting the integrator amplification according to the control deviation, control is slowed whenever the prescribed control deviation threshold is exceeded, which delays re-control to the target value. Further, this method is limited to a controller having an integral behavior represented by an integrator capable of receiving data separately and independently. Therefore, if this integration behavior occurs by interacting with other transmission members of the control system, it is inappropriate.

An object of the present invention is to provide a method for suppressing overshooting of a control circuit when a sensor for determining an actual value is slowed. Further, an object of the present invention is to provide a corresponding device.

In order to solve the problem of the present invention related to the above method, when changing the operating state for the preset time period, the control variable is more strongly limited than after the passage of the time period. Significant deviation between the set target and actual values due to a sensor with small dynamics when changing the operating state, for example in the early stages of control to regenerate a NO _x storage catalytic converter including a lambda sensor for determining exhaust gas lambda as a system variable The furnace control circuit is over-controlled. Limiting the control variable can suppress such overcontrol. After a change in the operating state, since a significant limit of the control variable is made only for a preset time period, and then a full range or a less strongly limited range of the control variable is provided again, the faulty control system can also be controlled to the desired target value. In order to ensure sufficient control parameters and bandwidth for subsequent control. The method can be particularly advantageously applied if the sensor used to measure the actual value can have at least often variable, undiagnosable dynamic deterioration over its lifetime. This is also suitable for control structures that do not include a transmission member in the form of an independent integrator.

Preferably, the preset time period for stronger limitation of the control variable may be preset according to the duration of the overshooting characteristic of the control system. Therefore, the initial overreaction of the control system is suppressed, and the possibility of fixing error correction is not continuously limited.

In addition, a preset time period for stronger limiting of control parameters may be preset according to the duration of each operating state. To this end, for example, the time at which the controller is active after the change of the operating state is measured and the control variable limit after the preset time period can be removed.

Depending on the application of the method, the system variable can be open-loop controlled in the first operating state and closed-loop controlled in the second operating state, and the control variable is more strongly limited when changing from the first operating state to the second operating state. do.

Corresponding to preferred variants of the invention, the control variable is limited to a fixed first limit value within a preset time period or the control variable is limited to a first limit value determined based on the characteristic map or characteristic curve. Pre-setting of the control variables by the characteristic map or characteristic curve enables optimum adaptation to the system behavior of the control system.

Corresponding to another variant of the invention, the upper and / or lower limits for stronger limits of the control parameters are multiplied by a fixed first coefficient or the upper and / or lower limits are first coefficients determined based on the characteristic map or characteristic curve. Can be multiplied with. In this case advantageously this restriction can always be selected as a continuous function and the jumps of the controller's control variables can be suppressed, but no additional ramp is used.

If the slowness of the sensor causes overshooting of the control circuit in only one control direction, this control variable 34 is more strongly limited to only one control direction of the control variable 34. In that case, control deviations in the opposite direction can be controlled in the overall control variable.

To enable fast control over the entire control range again after the initial overreaction of the control circuit, the control variable may be limited to the second limit value after a preset time period or the control variable may be multiplied by the second coefficient. At this time, the second limit value or the second coefficient is designed to be a larger control variable than the first limit value or the first coefficient.

Corresponding to a variant of the invention, the limit value can be changed along the ramp upon transition from the first limit value to the second limit value. At this time, the lamp may have a constant slope or a variable slope.

The above measures can be combined with one or more reset-windup-prevention measures, so that overshooting of the control circuit can be reduced.

In order to solve the problem of the present invention with respect to the above device, the control system includes a limiter for stronger limiting of control variables during a preset time period after a change in operating state. These limiters reduce the adjustable control variable after a change in operating state for a preset time period and after a large jump from the target value of the control variable, resulting in over-reaction of the control circuit based on the delayed dynamics of the sensor measuring the system variable. Can be suppressed. The above-described method can be implemented by such an apparatus.

Corresponding to a preferred variant of the invention, the control system can be implemented as a lambda control device of an internal combustion engine and a sensor as a lambda sensor. Lambda sensors can be suited and have a temporarily reduced dynamics. Due to the reduced dynamics of the lambda sensor, overreaction of the control circuit can be suppressed by temporary limitation of the control parameters.

The method and apparatus can preferably be applied to control the air-fuel ratio lambda when regenerating the NO _x storage catalytic converter in the exhaust duct of a diesel engine or gasoline engine.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

1 is a view showing a control signal and a sensor signal of a lambda control circuit during regeneration of a NO _x storage catalytic converter including an intact lambda sensor.
FIG. 2 is a diagram showing control signals and sensor signals of a lambda control circuit during regeneration of a NO _x storage catalytic converter including a slowed lambda sensor.
FIG. 3 is a diagram showing control signals and sensor signals of a lambda control circuit during regeneration of a NO _x storage catalytic converter including a slower lambda sensor and dynamic limitation of control parameters.
4 is a diagram showing a general structure of control variable limitation.
Fig. 5 is a diagram showing the block modification limit in the first embodiment.
6 is a diagram showing block modification limitations in the second embodiment.

1 shows control signals and sensor signals of a lambda control circuit during regeneration of a NO _x storage catalytic converter including an intact lambda sensor. To this end, the lambda sensor value 12, the controller output 13, the lambda target value 14 and the controller state 15 are displayed for the signal axis 10 and the time axis 11.

The NO _x storage catalytic converter and lambda sensor are located in the exhaust gas system of the internal combustion engine. The lambda control circuit is used to control the lambda value as a system variable in the exhaust gas of the internal combustion engine.

The control circuit not shown is constructed as follows. The lambda value is detected by the lambda sensor and provided to the comparator as lambda sensor value 12. In this comparator, a control deviation is formed based on the lambda sensor value 12 and the lambda target value 14 and provided to the lambda controller 20 shown in FIG. 4. The control variable as the controller output 13 forms the input signal of the control area. A preliminary control device may be provided which adds an output signal to the control variable, in some cases, but is not necessary and therefore not considered to describe the invention. The control area comprises an internal combustion engine with air and fuel supply and an exhaust gas system.

In the illustrated embodiment, the lambda control circuit is assigned to a diesel engine operated in lean mode in the first operating state as an internal combustion engine.

The NO _x storage catalytic converter is placed in the exhaust duct of an internal combustion engine to reduce nitrogen oxide emissions. During the first operating state in the lean operating mode of a diesel engine, the catalytic converter absorbs nitrogen oxides in the exhaust gas. If the storage capacity of the NO _x storage catalytic converter is exhausted, the nitrogen oxides stored therein are removed from the NO _x storage catalytic converter during the regeneration step. To this end, the internal combustion engine is operated in a rich mode, ie under-air, in the second operating state.

The adjustment of the rich mode operation is made by controlling the lambda to the corresponding lambda target value 14. To this end, the lambda controller 20 is activated corresponding to the controller state 15. Since the lambda controller 20 controls the control area for the duration of the regeneration phase, the lambda in the exhaust gas duct is <1.

In the illustrated embodiment, in the case of an intact lambda sensor, the lambda sensor value 12 is quickly adjusted to the lambda target value 14 after activation of the lambda controller 20. The controller output 13 proceeds to the required control value. After playback, the lambda controller 20 is deactivated corresponding to the controller state 15. The controller output 13 falls to the initial value and the lambda sensor value 12 rises again to a lean air-fuel ratio.

FIG. 2 shows the control signals and sensor signals of the lambda control circuit as already introduced with respect to FIG. 1 when regenerating a NO _x storage catalytic converter comprising a slowed lambda sensor. Here, the same reference numerals as in Fig. 1 are used.

In contrast to the behavior of the intact lambda sensor shown in Fig. 1, the slowed lambda sensor causes excessive controller interference. As a result, a significant shortage of the lambda target value 14 due to excessive reaction of the lambda controller 20 appears.

Since the lambda sensors can be contaminated by soot particles in the exhaust gas, the reaction time of the lambda sensor is inhibited. However, such suiting is not necessarily continuous, but rather can be reduced or completely eliminated by mechanical (vibration) or thermal (hot exhaust gas) effects. Also, not all lambda sensors are suited.

If the lambda sensor slows down beyond a certain scale due to the sooting, as a result, as shown in FIG. 2, the desired lambda value when starting the lambda control at the beginning of reproduction is significantly less. The lambda controller 20, which has designed the signal dynamics of the lambda sensor larger, attempts to control the lambda target value 14 by raising the control value (controller output 13). However, the measured lambda sensor value 12 does not reach the lambda target value 14 because the measured lambda sensor value 12 displays the actual state of exhaust gas very slowly due to the soot. As a result, the lambda controller 20 is over-controlled, which causes the lambda to actually be present in the exhaust gas as described above. Failure to achieve the desired target value may result in significant inhibition of exhaust emissions or, in the worst case, interruption in individual cylinders of the internal combustion engine.

FIG. 3 shows control signals and sensor signals of the lambda control circuit upon regeneration of the NO _x storage catalytic converter with slow limit lambda sensors and dynamic limits according to the present invention of control parameters. When the lambda sensor is slow In addition to the signal waveforms for the lambda sensor value 12 and the controller output 13, which have already been introduced in connection with FIG. 2, the controller according to the invention is also dynamically limited despite the slow lambda sensor. The waveforms of the output 13.1 and the associated dynamic lambda sensor value 12.1 are shown. In addition, the preset time period 36 is indicated by a double arrow.

According to the present invention, the control variable and the controller output 13 may be limited to the dynamically limited controller output 13.1 when changing the operating state for the preset time period 36. In the illustrated embodiment, the preset time period 36 starts the activation of the lambda controller 20 as indicated across the controller state 15. As an alternative, other variables that can derive the timing of the overreaction characteristics of the lambda controller 20 can also be used to start limiting the control parameters. The duration of the preset time period 36 adapts to the duration of the overshooting characteristics of the control system.

Since the control variable limit is changed after the operating state is changed, the lack of the lambda target value 14 is suppressed in the early stage of playback due to the actual lambda, but the control variable and the bandwidth can be sufficiently used during playback, so that there are many obstacles. These can also be controlled to the desired lambda target value 14. To this end, the control variable limit is removed after the preset time period 36 or a higher value is allowed for the control variable. Since the risk of overreaction of the lambda controller 20 is only in one control direction when changing the operating state from the lean operating mode to the rich operating mode, in the illustrated embodiment, the control variable is limited from lean to rich in only one control direction. do. Therefore, minimal influence of the control behavior is ensured.

In FIG. 4, the general structure of the control variable limitation in the example of the lambda control circuit described above is shown in a modular manner. The limiter 22 is connected downstream of the lambda controller 20. The unrestricted control variable 30, modified upper limit 32 and lower limit 33 output by the lambda controller 20 are provided to the limiter 22 as input signals. The modified upper limit 32 is formed by the block modification limit 21 provided with the upper limit 31. The limiter 22 and the block modification limit 21 may be integral elements of the lambda controller 20. The output control variable 34 as an input signal of the control region not shown corresponds to the controller output 13 shown in FIGS. 1 to 3.

The unrestricted control variable 30 output by the lambda controller 20 is limited at the upper and lower limits 31 and 33 by the limiter during normal operation. If the upper limit 31 and the lower limit 33 are properly selected, the control range corresponds to the limiting control variable 30 after the limiter 22.

When changing the operating state to regenerate the NO _x storage catalytic converter, the block modification limit 21 reduces the upper limit 31 for the preset time period to the modified upper limit 32. The limiter 22 reduces the output control variable 34 to the modified upper limit 32. As a result, excessive reaction of the lambda controller due to the delayed response of the lambda sensor can be suppressed. After the preset time period 36, the block correction limit 21 again outputs the maximum upper limit 31 to the limiter 22, and again the entire control range is provided for the outputted control variable 34.

FIG. 5 shows a first embodiment of the block modification limit 21 introduced in FIG. 4. The comparator 23 and the changeover switch 24 are assigned to the block modification limit 21. As an input signal, an active time controller 35 and a preset time period 36 shown in FIG. 4 are provided to the comparator 23. The switching signal 37 is output by the comparator 23 and provided to the switching switch 24. In addition, a start limit 38 and an upper limit 31 are provided to the switching switch 24.

The activation time controller 35 is determined by the start of regeneration of the NO _x storage catalytic converter and the activation of the lambda controller 20 associated therewith. The active time controller 35 is a time when the lambda controller 20 is active. If the active time controller 35 is shorter than the preset time period 36, the changeover switch 24 is controlled by the switching signal 37 such that the modified upper limit 32 corresponds to the start limit 38 do. At this time, the output control variable 34 shown in FIG. 4 is limited to the start limit 38. When the active time controller 35 exceeds the preset time period 36, the switching switch 24 switches and outputs the modified upper limit 32, which is greater than the start limit 38, provided the upper limit 31 Adjust with. Now, the limiter 22 can enlarge the control range for the control variable 34 output for the remaining reproduction time.

In the above embodiment, the preset time period 36 and the start limit 38 are set as fixed values. However, depending on which function enables optimal adaptation to the system behavior, it is also possible to set this by a characteristic curve or by a characteristic map.

6 shows a second embodiment of the block modification limit 21. The characteristic curve 25 and the multiplier 26 are assigned to the block correction limit 21. The coefficient 39 is formed by the characteristic curve 25 according to the active time controller 35, which is provided to the multiplier 26 together with the upper limit 31. Based on the upper limit 31 and the coefficient 39, the multiplier 26 forms a modified upper limit 32 for the control variable.

Based on the characteristic curve 25, this coefficient is determined after a change in the operating state according to the activation time of the lambda controller 20, that is, after the start of regeneration of the NO _x storage catalytic converter corresponding to the above-described embodiment. The upper limit 32 modified for the output of the control variable 34 is obtained by multiplying the coefficient 39 and the upper limit 31. At this time, the coefficient 39 decreases at the beginning of reproduction and then rises to the maximum value of 1. In this case advantageously this limitation is always a continuous function and the jump of the control variable of the controller can be suppressed without the use of additional ramps. The form of restriction can be easily adapted. Therefore, a continuous ascent of a plurality of steps of the limit or a limit in which the slope is variable may be possible.

Claims (13)

A method for controlling system variables of a control system operated in one or more first and second operating states when the values of the system variables are different,
A system variable detection step, wherein the system variable is detected by a sensor as an actual value, and the dynamics of the system variable change in a constant or unpredictable manner.
Determining a control deviation based on the actual value and the target value of the system variable and providing it to the controller of the control system;
And outputting the control variable 34 according to the control deviation,
When the operating state for the preset time period 36 is changed, the control variable 34 is more strongly limited than after the passage of the time period,
The system variable is open-loop controlled in the first operating state, closed-loop controlled in the second operating state, and the control variable is more strongly limited when changing from the first operating state to the second operating state. Method for controlling system variables. The system variable of the control system according to claim 1, characterized in that the preset time period (36) is preset according to the duration of the overshooting characteristic of the control system in order to further restrict the control variable (34). Method to control. The system variable of the control system according to claim 1 or 2, characterized in that the preset time period (36) is preset according to the duration of each operating state for stronger limitation of the control variable (34). To control it. delete The method according to claim 1 or 2, characterized in that the control variable (34) is limited to a fixed first limit value or a first limit value determined based on a characteristic map or characteristic curve in a preset time period. , A method for controlling system variables in the control system. 3. The method according to claim 1 or 2, wherein either or both of the upper and lower limits (31) and (33) are multiplied or fixed by a fixed first coefficient (39) to further restrict the control variable (34). Controlling system variables of the control system, characterized in that either or both of (31) and the lower limit (33) are multiplied with a first coefficient (39) determined based on the characteristic map or characteristic curve (25) Way for. Method according to claim 1 or 2, characterized in that the control variable (34) is more strongly limited in only one control direction of the control variable (34). 3. The method according to claim 1 or 2, characterized in that the control variable (34) is limited to the second limit value after the preset time period (36), or the control variable (34) is multiplied by the second coefficient (39). A method for controlling system variables of a control system. The method according to claim 5, characterized in that upon transition from the first limit value to the second limit value, the limit value varies along the ramp. delete As a control device for system variables of a control system, the control system has one or more first operating states and second operating states with different system variable values, and the control system includes sensors and control variables for determining the actual values of the system variables ( In the control device of the system variable of the control system having a controller for the output of 34),
The control system has a limiter 22 to more strongly limit the control variable 34 during a preset time period 36 after a change in operating state,
The system variable is open-loop controlled in the first operating state, closed-loop controlled in the second operating state, and the control variable is more strongly limited when changing from the first operating state to the second operating state. Control device for system variables. The control system system variable control device according to claim 11, characterized in that the control system is a lambda control device for an internal combustion engine, and the sensor is implemented as a lambda sensor. The control device of claim 11, wherein the control device is a device for controlling an air-fuel ratio lambda when regenerating a NO _x storage catalytic converter in an exhaust duct of a diesel engine or a gasoline engine.

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