CN110872975B

CN110872975B - Method for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle

Info

Publication number: CN110872975B
Application number: CN201910814814.1A
Authority: CN
Inventors: M.赫格德
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-08-31
Filing date: 2019-08-30
Publication date: 2024-04-26
Anticipated expiration: 2039-08-30
Also published as: DE102018214842A1; CN110872975A

Abstract

The invention relates to a method (100) for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle. The method is characterized in that the control and/or regulation of the SCR catalyst is carried out (108, 214, 216) as a function of at least one characteristic of a route which is in front of the motor vehicle and which the motor vehicle is to drive through in the future, wherein the at least one characteristic of the route can be detected or predicted.

Description

Method for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle

Technical Field

The invention relates to a method for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle, to a computer program, to a machine-readable storage medium and to an electronic control unit.

Background

As legal requirements for the emission values of internal combustion engines continue to increase, exhaust gases from the internal combustion engines are subjected to an aftertreatment in order to comply with predefined limit values. In order to meet these limit values, exhaust gas aftertreatment systems are used downstream of the internal combustion engine, the purpose of which is to reduce the concentration of particles and nitrogen oxides in the exhaust gas. The filters and catalysts used for this purpose require the introduction of specific oxidizing/reducing agents into the exhaust system.

These agents are typically hydrocarbons or aqueous urea solutions (HWL). The mentioned hydrocarbons, like for example diesel fuel, are used on the one hand for exothermic chemical conversions in oxidation catalysts (DOCs) in order to regenerate Diesel Particulate Filters (DPFs).

By means of the so-called Selective Catalytic Reduction (SCR) technology, the nitrogen oxide emissions of internal combustion engines, in particular diesel internal combustion engines, which operate with excess air can be reduced. In this case, nitrogen oxides are reduced to nitrogen and water vapor, with either gaseous ammonia or ammonia in aqueous solution or urea in aqueous solution being used as reducing agent. Urea is used here as ammonia carrier.

Urea is converted by means of hydrolysis into ammonia, which in turn then reduces the nitrogen oxides present in the exhaust gas in a true SCR catalyst, also called DENOX catalyst.

The main components of such a NOx reduction system are the reductant tank, the pump, the pressure regulator, the pressure sensor, the dosing valve and the controller, which can be either an electronic controller (in english: ecu= electronic control unit, electronic control unit) or a dosing controller (in english: dcu= Dosing control unit, dosing control unit). The pump delivers the reducing agent stored in the reducing agent tank to a dosing valve by means of which the reducing agent is injected into the exhaust gas flow upstream of the hydrolysis catalyst.

In the prior art, three problems described below are known in particular for SCR catalysts, which are briefly mentioned here below in terms of SCR filling level regulation (problem 1), SCR adaptation (problem 2) and active diagnosis of the SCR catalyst (problem 3). These three problems are briefly summarized below.

Fill level adjustment (problem 1): to be able to convert from NOx to N ₂, ammonia must be adsorbed on the SCR catalyst. While there are many factors that affect SCR conversion efficiency, ammonia storage in the SCR catalyst is an important factor that can be affected by the SCR catalyst system. The more ammonia stored in the catalyst, the higher the NOx conversion.

However, if there are conditions stored as the catalyst temperature increases, ammonia may desorb from the catalyst and result in the release of unconverted ammonia, known as ammonia slip. The more ammonia is stored in the catalyst at the low temperature of the catalyst, the more ammonia is released if ammonia slip conditions or conditions occur. Typical limit values for ammonia slip average 10ppm and 30ppm were used as maximum. Thus, in practice, the problem with urea dosing regulation is how to store enough ammonia in the SCR catalyst for achieving the desired emission target while limiting ammonia slip to within the necessary limits.

Due to the high temperature dynamics in the exhaust system of diesel vehicles, the NH ₃ storage capacity of the SCR catalyst is underutilized for reducing ammonia slip.

Although the SCR system may store more NH ₃ in a steady state at low temperatures, the NH ₃ storage limit is reduced in actual operation. However, under constant driving conditions, more NH ₃ can be stored in the SCR catalyst and thus higher NOx conversion efficiency can be achieved.

SCR adaptation (problem 2): the calculation of the necessary amount of ammonia to be stored and thus the amount of HWL used to reduce NOx can be affected by many errors and deviations, like for example engine raw emissions, catalyst conversion factors, inaccuracy of the dosing system itself, and deviations from the calculated filling level etc.

For this reason, the dosing deviation factor for the SCR system is learned and the dosing is adapted. The learning process of the dosing deviation factor is called adaptation or adjustment. The dosing amount is adapted by means of a NOx sensor which is arranged after the SCR catalyst or catalysts and which is cross-sensitive to ammonia if the NOx sensor arranged after measures high values (querempfindlich). The increase in NOx signal downstream of the SCR catalyst should be able to be attributed to higher NOx or NH ₃ slip.

The SCR fill level is reduced and the dosing is reduced during the SCR dosing adaptation for placing the system at a known operating point. Thereafter, the modeled and measured characteristics of the NOx signal downstream of the catalyst are compared, and a deviation coefficient or adjustment coefficient is then calculated.

Because the dosing is reduced, NOx emissions on the tailpipe increase during the adaptation.

An important condition for the adaptation is a constant exhaust gas temperature. If the temperature starts to change dynamically or leaves the optimal SCR operating range, the adaptation is interrupted. This means that if more favourable conditions are reached, the adaptation has to be restarted, and this may promote more NOx emissions on the tailpipe.

Active diagnosis of SCR catalyst (problem 3): SCR catalysts suffer from aging. If the SCR catalyst ages, its ability to store NH ₃ is typically reduced by a greater amount than the maximum achievable steady state storage capacity. This in turn reduces the efficiency of the catalyst. Thus, the NH ₃ storage capacity can be used as a standard for monitoring the SCR catalyst for meeting the increased diagnostic requirements of the overall SCR system.

Typically, a passive efficiency diagnostic is performed for the SCR catalyst. If the catalyst is found to be attractive or defective, an active diagnosis of SCR catalyst efficiency should be performed.

In the active diagnosis of the SCR catalyst, the catalyst is first overdose until the catalyst is filled. The fact that the catalyst is full is detected by: the NOx sensor signal downstream of the catalyst rises, that is, NH ₃ slip is detected. After detection of the NH ₃ slip, the dosing process is switched off for the indirect determination of the filling level therefrom, by: the efficiency during the so-called drain test is averaged. Since the dosing process remains shut off throughout the duration of the exhaust test, NOx emissions can only be converted by ammonia stored in the catalyst. In the case of a catalyst which functions as intended and has a greater capacity for storing NH ₃, the time required until the filling level is completely reduced is longer than in the case of an aged catalyst. Similarly, the efficiency of a catalyst that functions in a prescribed manner will also drop to zero more slowly. The efficiency obtained during the drain test is used by active SCR diagnostics to report errors.

During the over-dosing period, SCR efficiency and, thus, NOx emissions increase. However, emissions increase when emptied with a slightly aged catalyst. One of the important preconditions for active SCR diagnostics is a constant exhaust gas temperature. If the temperature begins to dynamically change or leaves the optimal SCR operating range, the diagnostic is discontinued. This means that if more favorable conditions are reached, an active diagnosis has to be restarted and this may promote more NOx emissions on the tailpipe.

Disclosure of Invention

The method is used for controlling and/or regulating an exhaust gas aftertreatment device, in particular an SCR catalyst, of an internal combustion engine arranged in a motor vehicle.

In this case, the control and/or regulation of the SCR catalyst is carried out as a function of at least one characteristic of the route which is in front of the vehicle and which the vehicle is to drive through in the future, wherein the at least one characteristic of the route can be detected or predicted.

The detection or prediction of at least one characteristic of the route is preferably carried out by a controller of the SCR catalyst.

This is advantageously achieved in that: exhaust gas aftertreatment devices, in particular SCR catalysts, can be controlled and/or regulated more effectively. In this case, the term "more efficient" means that the NOx emissions are reduced, the NOx conversion efficiency is improved and/or the SCR catalyst functions better in terms of energy.

At least one characteristic of the forward route is known if a navigation system in the vehicle is available or a road learning algorithm is available. Navigation systems typically provide information about average speed and grade. Thereby, the exhaust gas temperature can be predicted or calculated. This can also be seen by means of vehicle measurements performed experimentally. If the route conditions are stable for a certain section of the route, which can be recognized in advance by means of the navigation data, the dynamics of the exhaust gas temperature are reduced. The reduced dynamics of the exhaust gas temperature lead to a more efficient control and/or regulation of the SCR catalyst. The method thus advantageously achieves this, namely: the three problems mentioned above can be solved better and more effectively with knowledge of at least one characteristic of the future route of the motor vehicle. The solutions to the three problems described above are set forth below.

If stable driving conditions are detected, the SCR catalyst is operated according to a preferred embodiment in such a way that the NH ₃ filling level of the SCR catalyst increases. This represents a solution to problem 1. If stable driving conditions are identified, the controller of the SCR catalyst can increase the NH ₃ fill level in the SCR catalyst. In this case, the controller can predict the temperature dynamics and accordingly reduce the NH ₃ limit value to the normal limit for avoiding NH ₃ slip. This advantageously increases the NOx conversion efficiency of the catalyst in such a way that the catalyst storage capacity can be better utilized.

If a stable driving condition is detected for a future time, the control and/or regulation of the SCR catalyst can be optimized for the time between the current time and the future time at which the stable driving condition exists. Of course, the control and/or regulation of the SCR catalyst is likewise optimized for the time when stable driving conditions are present.

According to a further preferred embodiment, the SCR adaptation or SCR regulation is carried out at a position of the route where stable driving conditions are present and the exhaust gas temperature is within a predefined range. This represents a solution to problem 2. The controller can perform SCR adaptation on the route section where the driving conditions are stable and the exhaust gas temperature is within the required range, instead of starting the adaptation immediately after detecting an increased NOx signal downstream of the catalyst. This advantageously avoids an interrupted SCR adaptation and thus reduces NOx emissions.

According to a further preferred embodiment, the active diagnosis of the SCR catalyst is carried out at the location of the route where stable driving conditions are present and the exhaust gas temperature is within a predefined range. This represents a solution to problem 3. The controller can perform an active SCR diagnosis on the route section where the driving conditions are stable and the exhaust gas temperature is within the required range, instead of starting the active diagnosis immediately after the aged catalyst is detected by the passive diagnosis. This advantageously avoids an interrupted active SCR diagnostic, which in turn reduces NOx emissions and NH ₃ slip. For a slightly aged catalyst, the advantage is greater.

In other cases where no navigation data or route data is available, the controller must employ normal strategies, that is to say strategies that do not use route data or that must start with routes for which the characteristics of the route are statistically distributed.

According to a further preferred embodiment, at least one characteristic of the route in front of the vehicle and to be travelled by the vehicle in the future is acquired or predicted by means of a GPS receiver arranged in the vehicle and by means of a memory for a map arranged in the vehicle. The acquisition or prediction is preferably performed by a controller of the SCR catalyst. As an alternative or in addition to a memory for the map arranged in the vehicle, it can be provided that the method can access the cloud memory in which the map is stored, for example by a controller of the SCR catalyst. As an alternative to cloud storage, the internet can be used. This is advantageously achieved by this feature, namely: the method or the controller of the SCR catalyst can be used to obtain route characteristics, such as, for example, gradient or average driving speed, in a simple manner.

According to a preferred embodiment, the at least one characteristic of the route which is in front of the vehicle and which the vehicle is to drive through in the future is the gradient of the route and/or the speed to be driven, in particular the average driving speed. The map for each road section, which is available in the motor vehicle or in the cloud storage, preferably has information about the average speed and/or gradient of the road section. Both the average driving speed and the gradient of the route are together decisive factors for the instantaneous power of the internal combustion engine. The temperature of the SCR catalyst can be calculated from the instantaneous output power of the internal combustion engine.

The computer program is set up for: each step of the method is performed, in particular, when it is run on an electronic controller or a computer. This enables the method to be implemented on a conventional controller without having to make structural changes thereto. For this purpose, the computer program is stored on a storage medium that can be machine-readable. The electronic controller is obtained by loading the computer program onto a conventional electronic controller, which is set up to execute a method for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle.

Drawings

Embodiments of the present invention are illustrated in the accompanying drawings and explained in detail in the following description.

Fig. 1 and 2 show schematic flow diagrams of a method according to an embodiment of the invention, respectively.

Fig. 3,4 and 5 each show a block diagram of a method 100 for controlling and regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle according to a further embodiment of the invention.

Detailed Description

The method 100 for controlling and regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle, which is illustrated in fig. 1, begins in step 102 with the acquisition of the current GPS coordinates and the current speed and direction of travel of the motor vehicle. This acquisition is performed by means of GPS signals and a GPS receiver arranged in the motor vehicle. In a next step 104, the gradient and the expected average speed are acquired for each point of the route by means of a map stored in the motor vehicle for a route of 5km in front of the motor vehicle.

In a next step 106, a query is made as to whether a stable driving condition exists. If this is not the case, the method returns to step 102. If this is the case, the method continues with step 108, in which step 108 the SCR catalyst is operated such that the NH ₃ filling level of the SCR catalyst is increased.

In the figures, the cross indicates a negation of the inquiry, and the hook indicates a positive inquiry.

Fig. 2 shows a different embodiment of the method 100 from fig. 1. The method 100 starts here in step 202 with the acquisition of the current GPS coordinates and the current speed and direction of travel of the motor vehicle, as in the initial form of fig. 1. In a next step 204, the gradient and the expected average speed are acquired for each point of the route by means of a map stored in the motor vehicle for a route 5km in front of the motor vehicle.

In the next step 206, a query is made as to whether NH ₃ slip is occurring. If this is not the case, the method returns to step 202. If this is the case, the method continues with step 208, in which step 208 the most recent position of the route, in which stable driving conditions exist and the exhaust gas temperature lies within a predefined range, is detected from the map stored in the motor vehicle and by means of the GPS receiver. In a next step 210, a query is made as to whether the vehicle has arrived at the location acquired in step 208. If this is not the case, the method returns to step 208. If this is the case, the method continues with step 212, in which step 212 it is obtained whether SCR adaptation should be performed. If this is the case, the method continues with SCR adaptation in step 214. If this is not the case, the method continues with an active diagnosis of the SCR catalyst in step 216. The method returns to step 202 not only after step 214 but also after step 216.

Fig. 3 shows a block diagram of a method 100 for controlling and regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle. An embodiment of the method 100 is explained with reference to the block diagram.

In block 320, a current temperature of the SCR catalyst is detected by a temperature sensor 310 disposed on the SCR catalyst. In block 330, the SCR catalyst tuning function determines the necessary NH ₃ fill level based on the detected catalyst temperature and the amount of NH ₃ that is required for NOx reduction. In block 340, an adjustment to the NH ₃ fill level is made. In block 350, the required NH ₃ dosing is calculated.

Block 360 shows a GPS receiver 361, a map 362 for navigation, and a controller 365 that calculates the gradient and average speed of the route ahead of the vehicle from the received GPS signals. Preferably, the required data is acquired for a route of 5km in front of the motor vehicle.

In block 370, a temperature of the SCR catalyst is calculated for each point of the route in front of the vehicle. This is preferably done according to the modeled exhaust gas function or by means of the modeled SCR function.

In block 380, it is determined by means of the modeled SCR function when, that is to say at which point of the route in front of the vehicle, a constant temperature condition is present in the SCR catalyst.

If a constant temperature condition exists in the SCR catalyst, block 380 signals block 330 that the NH ₃ fill level should be shifted to another fill level.

Fig. 4 shows a block diagram of a method 100 for controlling and regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle. An embodiment of the method 100 is to be explained with the aid of this block diagram.

In block 420, a current temperature of the SCR catalyst is detected by a temperature sensor 410 disposed on the SCR catalyst. In block 430, the SCR catalyst tuning function determines the necessary NH ₃ fill level based on the detected catalyst temperature and the amount of NH ₃ required for NOx reduction. In block 440, an adjustment to the NH ₃ fill level is made. The required dosing amount of NH ₃ is calculated in block 450.

Block 460 shows a GPS receiver 461, a map 462 for navigation and a controller 465 which calculates the gradient and average speed of the route in front of the vehicle from the received GPS signals.

Slip downstream of the catalyst is detected by means of a NOx sensor 490 in block 492.

In block 470, the temperature of the SCR catalyst is calculated for each point of the route in front of the vehicle. This is preferably done in accordance with the modeled exhaust gas function and by means of the modeled SCR function.

In block 480, it is determined by means of the modeled SCR function when, i.e. at which point of the route in front of the vehicle, a constant temperature condition is present in the SCR catalyst.

If a constant temperature condition exists in the SCR catalyst, the NOx sensor 490 has previously detected slip, and the current temperature of the SCR catalyst determined in block 420 is within a predetermined range, an adaptation algorithm is implemented in block 494 that calculates an adapted dosing amount 496, followed by an adaptation of the dosing amount calculation performed in block 450. The SCR function then locates (platzieren) and triggers the adaptation at a location of the route where stable conditions can be expected and the temperature of the SCR catalyst is within the required range.

Fig. 5 shows a block diagram of a method 100 for controlling and regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle. One embodiment of the method 100 is to be explained in terms of this block diagram.

In block 520, a current temperature of the SCR catalyst is detected by a temperature sensor 510 disposed on the SCR catalyst. In block 530, the SCR catalyst tuning function determines the necessary NH ₃ fill level based on the detected catalyst temperature and the amount of NH ₃ that is required for NOx reduction. In block 540, an adjustment to the NH ₃ fill level is made. In block 550, the required NH ₃ dosing is calculated.

Block 560 shows a GPS receiver 561, a map 562 for navigation, and a controller 565 that calculates the gradient and average speed of the route in front of the vehicle from the received GPS signals.

In block 592, slip downstream of the catalyst is detected by means of a NOx sensor 590.

In block 593, an algorithm for passive diagnostics of the SCR catalyst is performed. Passive diagnostics check the function of the SCR catalyst without changing the dosing of the HWL. The passive diagnostic results are passed to block 594 where an algorithm for active diagnostics is performed. In contrast to passive diagnostic methods, the dispensing of liquid reactants is interfered with for diagnostic purposes in active diagnostic methods.

In block 570, the temperature of the SCR catalyst is calculated for each point of the route in front of the vehicle. This is preferably done in accordance with the modeled exhaust gas function and by means of the modeled SCR function.

In block 580, it is determined by means of the modeled SCR function when, i.e. at which point of the route in front of the vehicle, a constant temperature condition is present in the SCR catalyst.

If a constant temperature condition exists in the SCR catalyst, the NOx sensor 590 has previously detected slip, the current temperature of the SCR catalyst determined in block 520 is within a predetermined range, and the passive diagnostic acquired in block 593 has reported a fault, an algorithm for active diagnostics is implemented in block 594 that calculates a dosing amount 596 for active diagnostics, followed by an adaptation of the dosing amount calculation performed in block 550. The SCR function then locates and triggers an active diagnosis at the location of the route where stable conditions are expected and the temperature of the SCR catalyst is within the required range.

Claims

1. A method (100) for controlling and/or regulating an SCR catalyst of an internal combustion engine arranged in a motor vehicle,

It is characterized in that the method comprises the steps of,

Control and/or regulation of the SCR catalyst is carried out (108, 214, 216) as a function of at least one characteristic of a route which is in front of the motor vehicle and which the motor vehicle is to drive over in the future, wherein the at least one characteristic of the route can be detected or predicted, wherein the at least one characteristic of the route which is in front of the motor vehicle and which the motor vehicle is to drive over in the future is the gradient of the route and/or the speed of upcoming travel, wherein an active diagnosis of the SCR catalyst is carried out at a position of the route at which stable driving conditions are present and the exhaust gas temperature lies within a predefined range (216), wherein the SCR catalyst is operated in such a way that the NH ₃ filling level of the SCR catalyst is increased (108) if the stable driving conditions are detected.

2. The method (100) of claim 1, wherein,

The SCR is adapted to the position of the route where stable driving conditions exist and the exhaust gas temperature is within a predetermined range (214).

3. The method (100) according to any of the preceding claims, wherein,

At least one characteristic of the route is acquired or predicted by means of a GPS receiver (361, 461, 561) arranged in the motor vehicle and by means of a memory (362, 462, 562) for a map arranged in the motor vehicle, the route being in front of the motor vehicle and the motor vehicle being about to drive through the route in the future.

4. A machine-readable storage medium, on which a computer program is stored, which computer program is set up for carrying out each step of the method (100) according to any one of claims 1 to 3.

5. An electronic controller (365, 465, 565) set up for performing each step of the method (100) according to any one of claims 1 to 3.