Method for diagnosing a particle filter of a motor vehicle using a particle sensor connected downstream

Abstract

In a method for diagnosing a particle filter of a motor vehicle a particle sensor which is connected downstream and has a ceramic sensor element is used, wherein, for the particle sensor, regeneration (10) of the ceramic sensor element is provided by thermal heating to a specific temperature and for a specific time after the start of the motor vehicle. Within the scope of an on-board diagnosis a confirmed diagnosis result is output after a repeated occurrence of a first diagnosis result. In the proposed method reduced regeneration (40) of the ceramic sensor element takes place after a first diagnosis result (30).

Claims

1. A method for diagnosing a particle filter of a motor vehicle using a particle sensor which is connected downstream of the particle filter and that has a ceramic sensor element, the method comprising: regenerating (10) the ceramic sensor element by thermal heating the ceramic sensor element to a specific temperature and for a specific time after the start of the motor vehicle, diagnosing the particle filter to obtain a first diagnosis result (30), and performing reduced regeneration (40) of the ceramic sensor element after the first diagnosis result (30) to obtain a confirmed diagnosis result for the particle filter.

2. The method according to claim 1, wherein the specific time for the regeneration of the ceramic sensor element is shortened for performing the reduced regeneration (40) of the ceramic sensor element.

3. The method according to claim 1, wherein the specific temperature for the regeneration of the ceramic sensor element is reduced for performing the reduced regeneration (40) of the ceramic sensor element.

4. The method according to claim 1, wherein the conditions for performing the reduction of the regeneration of the ceramic sensor element are selected in such a way that at least some of the particles deposited on the ceramic sensor element are burnt off.

5. The method according to claim 1, wherein, for a measurement (20) with the particle sensor, applying an electrical voltage to the particle sensor and checking whether the resulting current is below a predefinable threshold value after a predefinable time period, wherein a fault is detected when the resulting current is above the threshold value.

6. The method according to claim 5, wherein the predefinable time period is shortened (50) up to the checking as to whether the resulting current is below the predefinable threshold value, after the execution of reduced regeneration (40) of the ceramic sensor element, wherein a fault is detected (60) if the resulting current is above the threshold value after the shortened time period.

7. The method according to claim 1, wherein, for a measurement with the particle sensor an electrical voltage is applied to the particle sensor subsequent to the reduced regeneration (40) of the ceramic sensor element, and it is checked (42) whether the resulting current is below the current value which had been measured before the reduced regeneration of the ceramic sensor element, wherein the reduced regeneration (40) of the ceramic sensor element is repeated when the resulting current is not below the current value which had been measured before the reduced regeneration of the ceramic sensor element.

8. The method according to claim 1, wherein reduced regeneration (40) of the ceramic sensor element is performed repeatedly after renewed occurrence of a detected fault.

9. The method according to claim 1, wherein in that a confirmed defect result (60) is inferred for the particle filter diagnosis if a fault is detected again after reduced regeneration (40) of the ceramic sensor element.

10. A non-transitory, computer-readable storage medium containing instructions that when executed by a computer cause the computer to control an exhaust system of a motor vehicle having a particle filter and a particle sensor which is connected downstream of the particle filter and that has a ceramic sensor element, by: regenerating (10) the ceramic sensor element by thermal heating the ceramic sensor element to a specific temperature and for a specific time after the start of the motor vehicle, diagnosing the particle filter to obtain a first diagnosis result (30), and performing reduced regeneration (40) of the ceramic sensor element after the first diagnosis result (30) to obtain a confirmed diagnosis result for the particle filter.

11. An electronic control device which is configured to control an exhaust system of a motor vehicle having a particle filter and a particle sensor which is connected downstream of the particle filter and that has a ceramic sensor element, by: regenerating (10) the ceramic sensor element by thermal heating the ceramic sensor element to a specific temperature and for a specific time after the start of the motor vehicle, diagnosing the particle filter to obtain a first diagnosis result (30), and performing reduced regeneration (40) of the ceramic sensor element after the first diagnosis result (30) to obtain a confirmed diagnosis result for the particle filter.

12. The electronic control device according to claim 11, wherein the specific time for the regeneration of the ceramic sensor element is shortened for performing the reduced regeneration (40) of the ceramic sensor element.

13. The electronic control device according to claim 11, wherein the specific temperature for the regeneration of the ceramic sensor element is reduced for performing the reduced regeneration (40) of the ceramic sensor element.

14. The electronic control device according to claim 11, wherein the conditions for performing the reduction of the regeneration of the ceramic sensor element are selected in such a way that at least some of the particles deposited on the ceramic sensor element are burnt off.

15. The electronic control device according to claim 11, wherein, for a measurement (20) with the particle sensor, applying an electrical voltage to the particle sensor and checking whether the resulting current is below a predefinable threshold value after a predefinable time period, wherein a fault is detected when the resulting current is above the threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention result from the following description of the exemplary embodiments in conjunction with the drawings. In this context, the individual features can each be implemented independently or in combination with one another.

(2) FIG. 1 shows a block diagram relating to the execution of an exemplary embodiment of the proposed method.

(3) FIG. 2 shows a block diagram of an electronic control device and a portion of an exhaust system.

DETAILED DESCRIPTION

(4) The FIGURE shows a block diagram illustrating the sequence of the proposed method in an exemplary embodiment. In step 10 at the start of a driving cycle, complete sensor regeneration is performed with the objective of completely burning off particles or soot from the ceramic sensor element of a particle sensor connected downstream of the diesel particle filter (DPF). After temperature equalization between the ceramic sensor element and the surrounding exhaust gas in a subsequent thermalization phase, a measuring phase 20 follows when the OBD diagnosis is requested. For this, a sensor measuring voltage is connected. When a predicted triggering time is reached it is checked whether the resulting sensor current is higher than a predefinable threshold value or not. If this threshold value is reached or exceeded, a fault is detected with respect to the DPF. If the threshold value is not reached (e.g. sensor current=0), an okay result is provided. After this first DPF-OBD result (fault or okay), the measuring phase is ended in step 30. According to the proposed method, after this DPF-OBD result, reduced sensor regeneration is performed at the start of the next measuring cycle in step 40 by, in particular, shortening or reducing the time for the sensor regeneration and/or the temperature for the sensor regeneration. In this context, the soot is not completely burnt off from the sensor element. Subsequently, in step 41 it is interrogated whether the sensor current which was measured for the DPF-OBD result in step 30 is higher than 0. If this is the case, a fault has been detected for the first OBD result. If this is not the case, an okay result has been detected as the first OBD result. In the first case, it is interrogated in step 42 whether the sensor current of the current measuring phase is lower than the sensor current before the reduced regeneration. If this is not the case, reduced regeneration is performed again by jumping back to step 40. In this step 42 it is therefore checked whether the conditions for the reduced sensor regeneration are selected such that part of the soot has already been burnt off during this reduced sensor regeneration, which becomes apparent from a reduction of the sensor current compared to the current before the regeneration. If the reduced sensor regeneration was not successful in this sense, the reduced sensor regeneration is repeated according to step 40. If the interrogation in step 42 reveals that the sensor current was lower after the reduced sensor regeneration than before the shortened sensor regeneration, there is a changeover to the measuring phase 50, wherein this measuring phase is carried out with a shortened predicted triggering time. If the interrogation in step 41 has revealed that in the DPF-OBD result the sensor current was not higher than 0 (okay result), it is possible to jump directly to the measuring phase 50 with a shortened predicted triggering time. This measuring phase 50 with a shortened predicted triggering time is based on the fact that after the reduced sensor regeneration 40 the soot collection phase of the sensor starts with residual soot already present, for which reason the time until the defect current threshold is reached is shorter. Therefore, the predicted triggering time of the sensor can be shortened in the measuring phase 50. In step 51 the interrogation takes place as to whether the resulting current in the case of the shortened triggering time is above the threshold value. If this is the case, in step 60 the outputting of a confirmed defect result for the DPF diagnosis takes place, and the measuring phase is ended. If the current is below the defect current threshold when the shortened triggering time is reached, in step 70 a confirmed okay result of the DPF diagnosis is provided and the measuring phase is ended. In a corresponding way, the described method is also suitable for diagnosing a particle filter of a spark ignition engine.

(5) The short circuit diagnosis of the particle sensor is expediently gated out at the end of the first reduced sensor regeneration 40, since otherwise the sensor operation could be blocked and no further reduced sensor regeneration would be possible. If the sensor current is still at the maximum after the repeated reduced sensor regeneration 40, a short circuit of the sensor element is present and the sensor operation is blocked. The shunt diagnosis is expediently gated out during the first and repeated reduced sensor regeneration 40, in order to prevent blocking of the sensor operation. In this context, the term shunt diagnosis is used if the sensor current is below a threshold or close to zero after complete sensor regeneration. In the case of reduced sensor regeneration according to proposed method there is provision that residual soot remains on the sensor element, which soot can, as intended, be measured as a current. This residual soot could incorrectly be detected as a shunt. Therefore, shunt diagnosis should expediently not be carried out after reduced sensor regeneration, and said shunt diagnosis should therefore be gated out.

(6) FIG. 2 shows a block diagram 100 that includes an electronic control device 110 having a computer 114 and a non-transitory computer-readable storage medium 118. The block diagram shows a particle filter 120 and a particle sensor 130 downstream from the particle filter. The particle sensor 130 includes a ceramic sensor element 134.