AT2410U1 - METHOD FOR REGENERATING A PARTICLE FILTER - Google Patents

Abstract

The invention relates to a method for regenerating a particle filter (4) of a diesel internal combustion engine (1), the regeneration being carried out as a function of the loading state of the particle filter (4). In order to be able to carry out the regeneration of the particle filter (4) as simply as possible, the flow cross-section is temporarily reduced downstream of the particle filter (4) during the regeneration process.

Description

AT 002 410 Ul

The invention relates to a method for the regeneration of a particle filter of a diesel internal combustion engine, the regeneration being carried out as a function of the loading state of the particle filter, and to a device for carrying out the method.

Particle filters are used in diesel engines in particular to filter out soot particles carried in the exhaust gas. To maintain the functionality of a particle filter, however, it must be regenerated if necessary.

In order to be able to regenerate a particle filter, it is necessary to increase the exhaust gas inlet temperature or the temperature in the particle filter for a short time in order to be able to influence the initialization of the regeneration.

Various methods for the thermal regeneration of particle filters are known. In the so-called stationary regeneration, the particle filter is burned out while the internal combustion engine is at a standstill by means of a motor-independent heating device provided for this purpose. Regeneration during motor vehicle operation is possible with the alternating regeneration, in which two parallel connected particle filters are alternately flowed through by the engine exhaust gas, while in each case the particle filter decoupled from the exhaust gas system for the time of thermal regeneration is flowed through by a heating gas temperature-controlled by an engine-independent heating device. Regeneration of the particle filter during motor vehicle operation is also possible with full-flow regeneration, in which the particle filter permanently in the exhaust gas stream is brought to the temperature required for regeneration in the regeneration phase, in which a heating gas stream generated by an engine-independent heating device mixes with the engine exhaust gas and together with this is introduced into the particle filter.

The known methods for the regeneration of particle filters require a relatively large construction effort and furthermore have the disadvantage that a separate heating device is required to heat the particle filter.

DE 42 30 180 A1 discloses a method and a device for determining the loading state of particle filters, in which filter-specific variables, such as pressure and temperature of the exhaust gas volume flow in the particle filter, and motor-specific variables, such as the engine speed, are measured. An actual characteristic value is calculated from the measured values, which is compared with a predefined limit characteristic value. If the actual characteristic value deviates sufficiently from the limit characteristic value, the regeneration process is initiated by activating an external burner device. Here, too, considerable design effort is required to carry out the regeneration of the particle filter. 2 AT 002 410 Ul

The object of the present invention is to avoid the disadvantages mentioned and to propose a method and a device in order to carry out a regeneration of the particle filter in a manner which is as simple as possible, depending on the loading condition.

The object is achieved according to the invention in that the regeneration is initiated by increasing the exhaust gas back pressure in the area of the particle filter, the flow cross section preferably being temporarily reduced downstream of the particle filter during the regeneration process. The increase in the exhaust gas back pressure leads to a rise in temperature in the particle filter, with a temperature of about 400 to 600 ° C. sufficient for regeneration to be reached. The temperature necessary for the regeneration can, if necessary, also be reduced by additives which promote oxidation. However, the increase in the exhaust gas back pressure can lead to an increased exhaust gas recirculation rate in internal combustion engines with exhaust gas recirculation and thus to a reduction in the oxygen content in the exhaust gas. In extreme cases, the oxygen deficit can mean that the regeneration of the particle filter cannot be continued. In order to avoid this and to provide the oxygen content in the exhaust gas necessary for the regeneration, it is provided in the context of the invention that the increase in the exhaust gas back pressure takes place during the regeneration phase, the flow cross-section downstream of the particle filter preferably being reduced and increased again in short cycle sequences. When the flow cross-section is reduced, the temperature in the particle filter rises just high enough to initiate and continue the regeneration. Before the oxygen deficit in the particle filter can become large enough to interrupt the regeneration, the flow cross-section is released again downstream of the particle filter, which leads to an increase in the oxygen content. Even before the temperature in the particle filter can drop below a size that hinders regeneration, the flow cross-section below the particle filter is reduced again and the exhaust gas back pressure increases, which again leads to a rapid rise in temperature.

Experiments have shown that an 80 to 95% reduction in the flow cross section is sufficient to be able to increase the exhaust gas back pressure sufficiently. The cycle time for reducing and opening the flow cross section is preferably between about one second and ten seconds.

In order to achieve a rapid expansion or reduction of the flow cross section, it is provided that the flow cross section is reduced by actuating a variable throttle, preferably a throttle valve or a slide. The variable throttle is connected to a corresponding control unit, which measures engine-specific and filter-specific operating parameters and determines the starting point of the regeneration phase and a pulse-width-modulated control signal for the variable throttle. To determine the start of regeneration, a characteristic characteristic value is calculated from the operating parameters and compared with a limit characteristic value. The pulse-width-modulated signal is necessary in order to be able to reach the required start temperature for 3 AT 002 410 Ul regeneration on the one hand, and on the other hand to be able to provide sufficient oxygen for the reaction in the particle filter during a successfully initiated regeneration phase.

It is advantageously provided that the characteristic parameter is calculated as a function of the engine speed n, the exhaust gas temperature T and the exhaust gas back pressure p upstream of the particle filter, a standardized exhaust gas back pressure p0 calculated according to the following relationship being used as the characteristic parameter: _ M idle Tjdle

Po Pa n Ta, where

Pa is the arithmetic mean of those measured within the time window Δΐ

Exhaust gas back pressure pi5

Ta is the arithmetic mean of those measured within the time window At

Exhaust gas temperatures T "

Tjd) e the exhaust gas temperature at idle speed n ^, n the engine speed measured during the time window Δί, n, which is the idle speed.

The regeneration by cyclically increasing the exhaust gas back pressure takes place over a predetermined total regeneration period tR. This predefined total regeneration time tR can be determined experimentally. In addition, instead of or in addition to the specified total regeneration duration tR, the regeneration success can be monitored by comparing the continuously determined characteristic characteristic value with the limit characteristic value. The regeneration is ended when the current characteristic value falls outside of a predefined range below the predefined limit value.

In order to ensure that the regeneration only takes place under optimal conditions, it is provided that the regeneration phase is interrupted if the measured values for the engine speed n or the exhaust gas temperature T are outside the ranges for the target speed or for the target exhaust gas temperature, and the regeneration phase is continued again as soon as the setpoint ranges are reached again.

In a preferred embodiment it is provided that during the

Regeneration phase a time counter is activated. As a result, the duration of the regeneration process is not unnecessarily suppressed by interruptions.

The invention is explained in more detail with reference to the figures. 4 AT 002 410 Ul

1 shows a block diagram of the device according to the invention for the regeneration of a particle filter, FIG. 2 shows an oxygen content-temperature diagram of the exhaust gas in the area of the particle filter, FIG. 3 shows a flow diagram to show the determination of the loading state of the particle filter, and FIG. 4 shows a flow diagram to show it regeneration monitoring.

In the block diagram shown in Fig. 1, only those parts are shown which are for the

Understanding of the invention are necessary. The internal combustion engine 1 is with the ✓

Intake line ^ and the exhaust line 3, shown. Particulate filter 4 / is inserted into exhaust pipe 3. Downstream of the particle filter 4, a variable throttle 5 is provided in the exhaust line 3, which can be designed, for example, as a throttle valve. A sensor 6 is used to detect the current engine speed n. Further upstream of the /

Particulate filter 4 in the exhaust pipe 3, a sensor 7 for measuring the exhaust gas back pressure p and a sensor 8 for measuring the exhaust gas temperature T are provided. If necessary, the '/ · *

Measurement of the particle filter temperature TF one or more temperature sensors 9 can be attached to the particle filter.

The values measured by the sensors 6, 7, 8 and 9 about the engine speed n, the exhaust gas back pressure p, the exhaust gas temperature T and possibly also the particle filter temperature T, F

v p

are fed to a control unit 10, which consist of CPU (Central Processor Unit), ROM v (Read Only Memory), RAM (Random Access Memory) and ADC (Analog / Digital Converter) and timers. The control unit 10 detects the measured values ps of the pressure sensor 7 and the measured values Tj of the temperature sensor 8 via a multiplexed analog input. The sensor signal of the speed sensor 6 is fed to a timer input after signal conditioning and the engine speed n is then calculated. The programming of the control unit 10 can be seen in the flow chart in FIG. 3 v. After starting the internal combustion engine, an initialization routine INIT is run in which, on the one hand, the CPU environment (ADC, RAM, timer etc.) is configured, and on the other hand, a preliminary diagnosis of the sensor input signals of sensors 6, 7, 8, 9 is carried out for plausibility. In a loop, which is preferably run every 500 ms, the samples of the exhaust gas back pressure p, and the exhaust gas temperature T; determined, and stored in RAM. This low sampling rate of 2 Hz has proven to be sufficient with the available time constants. The stored measured values are subsequently used to calculate the arithmetic mean value Ta of the exhaust gas temperature T upstream of the particle filter 4 and the arithmetic mean value pa of the exhaust gas backpressure p upstream of the particle filter 4, according to the following relationships:

Ta Pa

(1) (2) 5 AT 002 410 Ul

The normalized exhaust gas back pressure p0 is calculated from the two arithmetic variables Ta and pa, the variables 1 and k representing the number of measured values Tf and p. This normalized exhaust gas back pressure p0 represents a measure of the loading state of the particle filter 4. The normalized exhaust gas back pressure p0 is determined from the following relationship: _ M idle ^ idle P0 ~ Pa 'n Ta, (3) where

Pa is the arithmetic mean of those measured within the time window At

Exhaust gas back pressure ps,

Ta is the arithmetic mean of those measured within the time window At

Exhaust gas temperatures T "

Tidle the exhaust gas temperature at idle speed rijdle, n is the engine speed measured during the time window At, iW is the idle speed.

After this calculation of the standardized exhaust gas back pressure p0, a check is carried out of the conditions which determine the start of a regeneration phase. The following conditions are checked: T < Ta < T now - - max (4) < n < iw (5) Po ^ Psw (6)

If the conditions for a regeneration phase specified in equations (4) to (6) are fulfilled with a corresponding loading of the particle filter ^, the control algorithm for activating the variable throttle 5 designed as an exhaust gas throttle valve is activated. The rest position of the throttle 5 is expediently the

V open position. The program sequence for the control strategy of the throttle 5 is shown in FIG. 4. If the conditions for the regeneration start are met, a time counter is started after initialization of a time constant t. The variable tR determines the total time for a regeneration phase. The routine TCP (Throttle Control Procedure) generates a low-frequency pulse width modulated signal with the carrier frequency f = l / (ton + toff) and the duty cycle (Duty Cycle) DC = ton / (ton + toff) via a counter (COMPARE-TEMER) Controller and forwards this signal via a power driver to an electrical / pneumatic converter (overpressure modulator) for throttle 5. The variables ton and tojr represent time variables over the cycle time of the throttle 5. The 6 AT 002 410 Ul pulse-width-modulated signal enables a clocked opening and closing movement of the throttle 5 and thus a clocked reduction and expansion of the flow cross section downstream of the particle filter 4 . On the one hand, this allows the required start temperature for the regeneration of the particle filter 4 to be set and exceeded, y on the other hand, sufficient oxygen for the reaction in the particle filter 4 can be made available during a successfully initiated regeneration phase. As can be seen from the diagram shown in FIG. 2, the exhaust gas temperature T is contrary to the oxygen content 02 in the exhaust gas. The diagram shows the exhaust gas temperature T on the one hand and the oxygen content 02 over the opening time of the throttle 5. It should be noted that an opening time topCT = zero results in a very high exhaust gas temperature T, but a very low oxygen value 02. When the throttle 5 is continuously open, however, the opposite is the case. The opening time of the throttle 5 must therefore be selected such that </ the oxygen content 02 is sufficiently high for the regeneration of the particle filter 4 and the exhaust gas temperature T.

After the pulse-width modulated signal has started, it is checked whether the permitted temperature and speed range is maintained. The reaction can be monitored in a controlled manner via the temperature TF in the particle filter 4. If the current exhaust gas temperature T in front of the particle filter is less than Tmin, the regeneration phase is interrupted since the current operating conditions of the internal combustion engine no longer guarantee successful regeneration. The current count value of the time variable t is stored and, when the throttle valve procedure TCP is started again, only the difference is processed until the total regeneration duration tR is reached. This measure ensures that the duration of the regeneration process is not unnecessarily extended by interruptions. The throttling procedure is only started again when the corresponding conditions are met. If the temperature T rises above TTOX, the regeneration is also interrupted in order to prevent thermal overloading of the particle filter 4. Compliance with the

V

Speed range n ^ &lt; n &lt; n ^ is used to avoid extreme operating conditions of the internal combustion engine. In order to be able to influence the regeneration of the particle filter ^., The pulse duty factor of the pulse-width-modulated signal for controlling the throttle 5 can be changed. A measure of the degree of regeneration is the standardized exhaust gas back pressure p0. If the end of the regeneration occurs before the total regeneration duration tR has elapsed, the procedure is ended by falling below a predefined tolerance range Apsw below the limit parameter psw. The value tR for the total regeneration time represents an average time value from previous experimental tests. The regeneration process should be completed in most cases within this time period tR. If the time tR has elapsed, the throttling procedure is ended. A waiting procedure designated WAIT in FIG. 4 is then started, during which all actions are blocked. The blocking time serves to determine possible changes in the normalized pressure p0 calculated from mean values and thus to be able to assess the success of the regeneration. If a regeneration was successfully carried out, p0 has dropped far below the limit characteristic value psw, and only the main routine shown in FIG. 3 7 AT 002 410 U1 will subsequently be run through. If the regeneration was not successful, the control algorithm shown in FIG. 4 for the throttle 5 can be carried out again immediately when the corresponding conditions are reached. This process is then repeated until a successful regeneration has taken place. 8th

Claims (14)

AT 002 410 Ul CLAIMS 1. Method for the regeneration of a particle filter (4) of a diesel internal combustion engine (1), the regeneration being carried out as a function of the loading state of the particle filter (4), characterized in that the regeneration is carried out by increasing the exhaust gas back pressure (p ) is initiated in the area of the particle filter (4), the flow cross section preferably being temporarily reduced downstream of the particle filter (4) during the regeneration process. 2. The method according to claim 1, characterized in that the increase in the exhaust gas pressure (p) takes place clocked during the regeneration phase. 3. The method according to claim 2, characterized in that the flow cross section is reduced by at least 70%, preferably between 80% to 95%. 4. The method according to claim 2 or 3, characterized in that the cycle time for the reduction and for opening the flow cross section is 1 to 10 seconds. 5. The method according to any one of claims 1 or 4, characterized in that the reduction of the flow cross-section is carried out by actuating a variable throttle (5), preferably a throttle valve or a slide. 6. The method according to any one of claims 1 to 5, characterized in that to determine the loading state of the particle filter (4) within a time window (At) current engine-specific and filter-specific operating parameters (η, T, p) are detected that from the current operating parameters (η, T, p) a characteristic parameter (p0) is calculated, and this is compared with a limit parameter (psw). 7. The method according to claim 6, characterized in that the characteristic parameter as a function of the engine speed (n), the exhaust gas temperature (T) and the exhaust gas back pressure (p) upstream of the particle filter (4) is calculated, with a characteristic parameter according to the following Relationship of calculated normalized exhaust gas back pressure (p0) is used: _ M idle Tjdle Po Pa n Ta, where Pa is the arithmetic mean of the exhaust gas back pressures Pj, 9 AT 002 410 Ul Ta the arithmetic mean of the exhaust gas temperatures Tj5 measured within the time window At Tid) e is the exhaust gas temperature at idle speed n ^, n is the engine speed measured during the time window At, n ^ is the idle speed. 8. The method according to any one of claims 1 to 7, characterized in that due to the loading state of the particle filter (4) by a control unit (10) determines the start of regeneration and generates a pulse-width modulated control signal and the actuator of the variable throttle (5) during the regeneration phase of Particle filter (4) is supplied. 9. The method according to any one of claims 1 to 8, characterized in that the regeneration takes a predefined total regeneration duration (tu) long and / or until the characteristic parameter (p0) is smaller than the limit parameter (psw). 10. The method according to any one of claims 1 to 9, characterized in that a time counter (t) is activated during the regeneration phase. 11. The method according to any one of claims 1 to 10, characterized in that the regeneration phase is interrupted when the measured values for the engine speed (n) or the exhaust gas temperature (T) outside the ranges for the target speed (n ^, or for the Desired exhaust gas temperature (Tmin, T ^ lie, and the regeneration phase is continued again as soon as the setpoint ranges are reached again. 12. The method according to claim 10 and 11, characterized in that when the regeneration phase is interrupted, the time counter (t) is stopped and, when the regeneration phase is continued, the time counting is continued until the total regeneration duration Or) has been reached. 13. Device for the regeneration of a particle filter (4) of a diesel internal combustion engine (1) with measuring devices (6, 7, 8) for determining the engine speed (n), the exhaust gas temperature (T) and the exhaust gas back pressure (p) in the exhaust system (3) upstream of the particle filter (4), the measuring devices (6, 7, 8) being connected to a control unit (10) which, based on the measured values (η, pi5 Τ (, p0, n, Ta), determines the actual values Compares the state with target values (pswi, n ^ ,,, n ^, Tmin and initiates the regeneration of the particle filter (4) as a function thereof, characterized in that a variable throttle (5), preferably a throttle valve, downstream of the particle filter (4) , arranged in the exhaust line (3), which can be actuated in a clocked manner by the control unit (10) 10 AT 002 410 Ul 14. The apparatus according to claim 13, characterized in that at least one measuring device (9) for detecting the temperature (TF) in the particle filter (4) are additionally provided, which is connected to the control unit (10). 11