AND MACHINE

TECHNICAL FIELD

The present invention relates to a method for cleaning an exhaust diesel particulate filter (DPF) from soot particles trapped in use.

BACKGROUND OF THE INVENTION

Exhaust Particulate Filters (DPF) are provided in the exhaust system of many internal combustion engines. The DPF comprises of thousands of juxtaposed channels extending along a main direction from a front face to a rear face. In said faces the channels open and form regular two-dimensional networks of open cells. Alternate channels are plugged. The plugs force the exhaust flow through the walls separating each channel and the particulate collects on the inlet face. In use, soot particles present in the exhaust gases of an internal combustion engine are trapped within said channels and, regularly the DPF needs to be cleaned.

Well-known cleaning machine utilize a pressurized air stream directed to the front face, said stream pushing the particles along the channels in the DPF.

Improvements have been made in dividing the front face of the DPF into several sectors, each comprising several cells and by blowing sector by sector and thus scanning all the front face of the DPF.

Utmost efficiency of the cleaning process is required to minimize the cleaning cycle duration while ensuring maximum regeneration and renewed performances of a used DPF.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a method to clean a diesel particulate filter (DPF) , said DPF comprising a plurality of juxtaposed channels extending along a main axis from a front face to a rear face in which said channels form two- dimensional array of cells so that, in use, soot particles present in the exhaust gases of an internal combustion engine are trapped within said channels. Also, the DPF is arranged in an air-cleaning machine having a nozzle adapted to blow an incident air jet along said main axis toward the front face of the DPF, said machine being further provided with a pressure sensor adapted to measure a second pressure of a reflected air stream bouncing on the front face and deflecting toward the nozzle, an electronic control unit (ECU) controlling the machine and executing the method which comprises the steps of:

positioning the nozzle before a sector of the front face , said sector comprising a plurality of juxtaposed cells;

setting a first counter at predetermined initial value, for instance zero; blowing pressurized air toward the sector selected at step a for a predetermined cycle time and;

measuring the second pressure of the reflected air stream bouncing on the front face;

comparing said second pressure at completion of said cycle time to a predetermined 'clean' threshold then;

if said second pressure is below the threshold then consider said sector being clean or:

if said second pressure is above the threshold then consider said sector being dirty then, increment the counter by one, and:

if the counter has reached a predetermined maximum value

corresponding to a maximum number of repeat of step then confirm the sector as 'dirty' and record the address of said 'dirty' sector or;

if the counter has not reached the maximum value then repeat the blowing step.

Method further comprises the step:

if the sector is considered 'clean' as per criteria or, if the sector is confirmed 'dirty' as per criteria the method considers whether said all sectors of the DPF have been selected at least once and:

if all sectors of the DPF have been selected then end the method;

if all sectors have not been selected then performs a step of moving the nozzle before another sector and repeat the method at the positioning step until all sectors of the DPF have been selected. The method further comprises the step:

h determining a pass/fail end-criteria and, identifying the DPF as being:

- "cleaned", if said end-criteria is pass or,

- "dirty", if said end-criteria is fail.

Said pass/fail end-criteria is the ratio of dirty sectors.

The incident air jet has a first pressure superior to 5 bars, preferably between 7 and 20 bars.

At positioning step the outlet opening of the nozzle through which the air stream is blown is in close vicinity or preferably in contact with the selected sector.

The invention further extends to an electronic control unit adapted to pilot a DPF air cleaning machine as per the method described above.

The ECU operates by executing a software recording the steps of a method.

The invention extends to a DPF air cleaning machine adapted to execute a method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is an axial section illustrating the flow path through adjacent channels of a DPF.

Figure 2 is a front view of the DPF of figure 1 having certain cells cleaned and other dirty.

Figure 3 is a sketch representing the DPF under air-cleaning process, the cells subject to the cleaning process being obstructed.

Figure 4 is similar to figure 3, the cells subject to the cleaning process being cleaned.

Figure 5 is a plot of a measure of a back air flow pressure measured during the process of figures 3 and 4.

Figures 6 is a flow diagram of the cleaning method as per the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures, a diesel particulate filter 10, hereafter DPF, has a general cylindrical shape extending along a main axis X between a transverse front face 12 and a transverse rear face 14 and, it comprises thousands of parallel channels 16 extending between said transverse faces. The channels 16 are plugged either at their end in the front face 12 or at their end in the rear face 14, more precisely, if plugged at the front face 12, then all adjacent channels 16 are plugged at the rear face 14. As shown on figure 1, the only way for flow to travel from the front to the rear face is through the walls separating each channel 16.

When the DPF 10 is new the channels 16 are perfectly clean creating in each of the front 12 and rear 14 faces a regular two-dimensional array of juxtaposed cells 18.

In use, exhaust gases flow through the DPF 10 and, soot particles S present in said flow accumulate and finally obstruct some of the channels 16.

A simplified exemplary embodiment of a DPF is represented on figures 1, 2, 3 and 4, the DPF 10 having the shape of a cylinder of revolution extending about the main axis X, the front 12 and rear 14 faces being circular discs and, each cell 18 forming a small hexagon in said faces forming a honeycomb structure. These geometrical characteristics are proposed as example only and should not be read as limitation to the scope of the invention, non-circular DPF and non- hexagonal channels and cells are known.

As shown on figure 2, certain cells 18 are dark symbolizing cells obstructed 180 by soot particles S and, others are white symbolizing clean cells 18C. Regularly the DPF 10 has to be cleaned and particles S are removed in an air-cleaning machine 30.

In the machine 30, the DPF 10 is arranged in a cleaning chamber and, an electronic control unit 32, hereafter ECU, controls the cleaning operation of the DPF 10. In particular, pressurized air forming an incident jet Al having a first pressure PI is blown via a nozzle 34 in the direction of the main axis X toward the front face 12. While for clarity and simplification purposes the nozzle 34 is represented on figures 3 and 4 distant from the from face 12 of the DPF 10, favorable results have been obtained in machines where the nozzle 34 is in direct contact with the front face 12. The pressure of the incident jet Al is normally above 5 bar within a range of 5 to 20 bar.

When said incident jet Al faces an obstructed cell 180, as shown in figure 3, the air bounces on the front face 12 and a reflected jet A2 deflects toward the nozzle 34. Said reflected jet A2 has a second pressure P2 measured by a pressure sensor 36 arranged on the nozzle 34. The pressure sensor 36 is connected to the ECU 32 and, the second pressure P2 is therein recorded.

When said incident jet Al faces a clean cell 18C, or a cell from which obstructing particles S have been removed as shown in figure 4, the incident jet Al enters the DPF via the front face 12, it follows the channels 16, passes through the channel walls and exits by the rear face 14. A minor portion of the incident jet Al still bounces on the front face 12 and a small refiected jet A2 deflects but, the second pressure P2 of said small jet A2 is much lower than in the previous case when facing obstructed cells 180. As depicted on the figures, when the incident jet Al enters a cell, it pushes the dirty soot particles S through the channels 16, said particles S exiting by the rear face 14.

The cleanliness of a channel 16 is therefore sanctioned by monitoring the second pressure P2 of the reflected jet A2. Figure 5 is a plot of three curves CI, C2, C3 representing in three different cases, the evolution of the second pressure P2 as a function of time t.

The first curve CI , the lowest of the three, is measured in the case of the incident jet Al facing cells that are almost clean. At beginning of the process the second pressure P2 is 4 bar and, within 250 milliseconds said second pressure P2 drops to 2 bar indicating a small reflected jet A2 and clean cells.

The second curve C2, the middle one, is measured in the case of the incident jet Al facing cells less clean than previously. For instance the incident jet Al may face several cells, some being obstructed 180, the other being clean 18C or "partially" clean. At beginning of the process the second pressure P2 is over 4 bar, almost 5 bar and, within 250 milliseconds said second pressure P2 drops to 3 bar indicating a small reflected jet A2 and clean cells. Still, said clean cells are not as clean as in the first case since, at the end of the cycle, the reflected jet A2 has a higher pressure, 3 bar, than in the first case, 2 bar, this indicating that the incident jet Al has more difficulty to flow the DPF. For instance, the incident jet Al may have opened part of the cells while others remained obstructed, generated said reflected jet A2.

The third curve C3, the top curve, is measured in the case of the incident jet Al facing obstructed cells 180. At beginning of the process the second pressure P2 is over 7 bar and, within 250 milliseconds said second pressure P2 slightly drops to 5.5 bar indicating that the reflected jet A2 remains important at the end of the cycle. For instance, the incident jet Al may face several cells that are all obstructed 180 and, only very few get cleaned within said cycle time.

Prior to detailing the cleaning process, a few points observed as being helpful to the cleaning process are now highlighted.

The nozzle 34, wherefrom the incident jet Al exits, is in direct contact with the front face 12 and, as said above, for clarity purposes the figures 3 and 4 show a distance from the nozzle to the front face 12 and also, diverging air jets Al, A2.

It is also favorable to house the pressure sensor 36 as close as possible within the nozzle assembly block, this in order to minimize the distance to the front face 12 and to improve the measurement quality of the second pressure P2, the cleanliness of a cell being characterized by the value of said second pressure P2. A cell can be considered clean 18C when said second pressure P2 has dropped to a "clean" threshold P2C, for instance 2 bar as shown on the example of the first curve CI of figure 5.

It is also of interest, although not being mandatory, to divide the front face 12 of the DPF into several sectors 20, each grouping a plurality of juxtaposed cells 18. For instance to keep dimensions reasonable a sector 20 may group nine cells substantially forming a square or a circle. Another interest of said multi-cells sectors 20 is that since several cells are subject simultaneously to the incident jet Al, certain cells may clean while others remain obstructed, this generating for a sector 20 a second pressure P2 intermediate between the fully clean and the fully obstructed, such as the second curve C2, and enabling better interpretation of the results.

Full automation of the machine 30 enables to move the nozzle 34 relative to the front face 12 in order to automatically scan the complete surface of said front face 12. Displacement can be of the nozzle 34 alone, for instance an horizontal translation along a diameter and, when reaching the end translating vertically to a next row, until the front face has been totally scanned. Also, combined movements of the nozzle 34 and of the DPF 10 may achieve similar scanning objective, for instance by radially translating the nozzle 34 while rotating the DPF about the main axis X. In any case, the displacements are done step by step, stabilizing position between each step in order for the nozzle 34 to face a specific sector 20 and perform the cleaning process on said specific sector 20.

Thanks to measuring said second pressure P2, the cleaning process is automatized from beginning when installing the dirty DPF in the machine 30 to, end when removing the cleaned DPF. At completion of a cycle time T, that is 250 milliseconds in the examples of figure 5, measure of the second pressure P2 indicates if the sector is sufficiently cleaned. If so, the nozzle 34 is move to another sector 20, without the need for a repeated cleaning jet on said sector.

The second pressure P2 is measured and used as a pass/fail criteria when compared to the 'clean' threshold P2C. If at completion of the cycle T, the second pressure is below the threshold P2C then, the nozzle 34 is moved to another sector and, if said second pressure P2 is above the 'clean' threshold P2C then the air jet cleaning cycle is repeated until a maximum number of repeat is reached. In the latter case, the sector is considered 'dirty' or 'obstructed' and its address within the front face 12 is recorded. Said address can be recorded in term of any coordinate system such as X-Y Cartesian coordinate or as radius-angle polar coordinates. The address, or positional data, is recorded and displayed to give the user a graphical indication of which area the DPF has a 'dirty' sectors '20O' occurred in.

The nozzle 34 is moved from sector to sector until all sectors defining the front face 12 have been selected, said displacement of the nozzle before the entire first face 12 corresponding to a scan of the front face 12.

At completion of a first scan of the front face 12, the DPF 10 may be considered "clean" or still "dirty" depending on the value determined for a pass/fail end-criteria EC, for instance if the number of 'dirty' sector 20O is superior to a certain number or, in calculating the ratio of number of obstructed sectors 20O over the number of clean sectors 20C, the lowest said ratio is, the cleaner the DPF 10 is and, above a predetermined threshold of said ratio the DPF is considered "dirty".

Also, at completion of the first scan, if an DPF is considered "clean", the process ends and the clean DPF is removed from the machine 30 but, if it is considered "dirty" as per the above end-criteria EC, a second scan may be performed. Similarly at completion of the second scan, a subsequent third and others scan may be run. To end the process, the maximum number of scan is set and the end-criteria EC of cleanliness is determined to finally consider said DPF clean or dirty.

A step-by- step method 100 of the "DPF smart cleaning process" is now detailed in reference to figure 6, the method 100 being executed by a software 40 uploaded onto the ECU 32. The steps of the method 100 are as follow:

a) positioning 110 the nozzle 34 before a sector 20 of the front face 12, said sector 20 comprising a plurality of juxtaposed cells 18;

b) setting 120 a first counter C at zero;

c) blowing 130 pressurized air jet Al toward the sector selected at step a) for the predetermined cycle time T, which in the example of figure 5 is 250 milliseconds and;

d) measuring 140, with the pressure sensor 36, the second pressure P2 of the reflected air stream A2 bouncing on the front face 12;

e) comparing 150 the second pressure P2 at completion of said cycle time T to a predetermined 'clean' threshold P2C, which in the example of figure 5 can be 2 bar, then:

el) if said second pressure P2 is below the threshold P2C then consider 160 said sector being clean 20C and:

e2) if said second pressure P2 is above the threshold P2C then consider 170 said sector being dirty 20O then, increment the counter C by one, and

e2a) if the counter C has reached a predetermined maximum value Cmax corresponding to a maximum number of repeat of step c) then confirm the sector as 'dirty' 20O and record 180 the address of said 'dirty' sector 20O. As mentioned above, the address of the 'dirty sector' can be done using any coordinate system that will enable to locate said sector within the front face 12. e2b) if the counter C has not reached the maximum value Cmax then repeat the blowing step 130;

f) if the sector is considered 'clean' 20C as per criteria el) or, if the sector is confirmed 'dirty' 20O as per criteria e2a), the method wonders whether said all sectors have been selected at least once and:

fl) if all sectors of the DPF have been selected then end 200 the method;

f2) if all sectors have not been selected then performs a step 190 of moving the nozzle 34 before another sector 20 and repeat step a) until all sectors 20 of the DPF 10 have been selected. This step g) is a loop wherein the nozzle 34 is moved from one sector to another sector until all sectors have been cleaned and a complete scan of the front face been performed.

h) determining the pass/fail end-criteria EC and, identifying the DPF 10 as being:

- "cleaned", if said end-criteria EC is pass or,

- "dirty", if said end-criteria EC is fail.

Thanks to this step-by-step method 100 which constantly performs a diagnoses a sector and the complete DPF, the method optimizes the cleanliness of the DPF while reducing the overall process time.

LIST OF REFERENCES:

X axis

S soot particles

Al incident jet

A2 reflected jet

PI pressure

P2 second pressure

P2C second pressure - clean threshold

T cycle time

EC end criteria

C counter

10 diesel particulate filter - DPF

12 front face

14 rear face

16 channels

18 cells

18C clean cell

180 obstructed cell - dirty cell

20 sector

20C clean sector

20O obstructed sector - dirty sector

30 machine

32 electronic control unit - ECU

34 nozzle

36 pressure sensor

38 machine display

40 software

100 method

1 10 positioning

120 counter setting

130 blowing

140 measuring

150 comparing

160 ending - clean sector

170 incrementing counter

180 dirty sector confirmed

190 moving

200 ending