METHOD AND APPARATUS FOR CONTROLLING THE REGENERATION OF AT LEAST ONE PARTICULATE FILTER INSTALLED IN A DIESEL ENGINE

Abstract: The method comprises periodical checking of the level of clogging of the particulate filter, and if a decrease in clogging level is found which has not resulted from intentional regeneration the threshold at which intentional regeneration is initiated is lowered until, if necessary, the intentional regeneration is initiated.

Description: This invention relates to a method and apparatus controlling the regeneration of at least one particulate filter installed in a diesel engine of non-supercharged or supercharged type. As is well known, triggering and controlling the combustion of particles which have accumulated within a particulate filter (also known familiarly as a trap) are still the two major problems to be solved in the development of an efficient filtration system for the exhaust gas of a diesel engine. In this respect, the periodical process of oxidising the trapped carbon particles, commonly known by the term regeneration, is necessary in order to maintain the back pressure on the engine exhaust at an acceptable level. In the same manner, regeneration control is necessary to prevent excessive temperature being reached during particulate combustion, with possible destruction of the filter. Regeneration is effected in various ways, but generally by operating thermal energy generators (burners etc.) when it is considered that the clogging of the filter has reached a suitable level between a maximum and a minimum limit. The maximum limit is determined, as stated, by the need to avoid both excessive back pressure on the engine exhaust, with unacceptable deterioration in performance, and too high temperature during regeneration, which could lead to breakage of the filter. More critical is the required minimum amount of particulate which has to be accumulated before regeneration can be initiated. If the quantity of particulate trapped in the filter is small there would certainly be no excess temperature, but in this case combustion would not be complete as the propagation of the flame front, for example in the last part of a ceramic filter, is sustained by the thermal energy released by the combustion of the carbon particles of the particulate. It often happens that regeneration is triggered spontaneously when the quantity of particulate has not yet reached the aforesaid minimum level, so that combustion is not sustained. Thus at the end of regeneration there still remains particulate in the last part of the filter, this particulate then being added to that which collects during the next accumulation period. The initiation of the next regeneration on the basis of an average clogging evaluation could lead to irreversible damage to the filter. This is because the particulate will have accumulated to a larger extent in certain zones of the filter, with consequent greater development of thermal energy deriving from the combustion of the particulate. A further drawback of current regeneration control systems is that the evaluation of the filter clogging is done by instruments the measurements of which could be affected by systematic errors or by errors consequent on particular environmental conditions such as the temperature at which the reading is taken. It is apparent that this situation can lead to the regeneration being initiated either early or late, leading to all the aforementioned consequences. From the US-A-4 603 550, it is also known an exhaust particilate removing system, wherein the regeneration of the filter is effected by operating a burner controlled by a control unit in response of a signal corresponding to the difference of pressure between the inlet and the outlet, a signal of the temperature within the burner, and other signals of the operating conditions of the engine. The object of the present invention is to provide a method and apparatus for controlling the regeneration of particulate filters for diesel engines which obviate the aforesaid drawbacks of the current systems. Said object is attained according to the present invention by a method controlling the regeneration of at least one particulate filter installed in a diesel engine, wherein the level of clogging of said filter caused by progressive accumulation therein of the particulate is periodically calculated, and wherein an intentional regeneration of said filter is caused when said clogging level reaches a predetermined upper clogging limit, characterized by periodically comparing the last calculated clogging level with the previous calculated clogging level after said intentional regeneration; and defining a new upper clogging limit progressively lower than the previously defined upper clogging limit each time said comparison reveals a reduction of said clogging level. Said object is further attained according to the present invention by a device controlling the regeneration of at least one particulate filter installed in a diesel engine, according to the above method, comprising means for measuring quantities related to the clogging of said filter by said particulate, means for processing said quantities and calculating the level of clogging of said filter caused by the progressive accumulation of said particulate, means for memorizing a predetermined upper clogging threshold for said filter, and regeneration means adapted to be controlled for an intentional regeneration of said filter when said level of clogging exceeds said predetermined clogging threshold, characterized by comparing means for periodically comparing the last clogging level calculated by said processing means with the previous calculated clogging level after said intentional regeneration, and control means responsive to said comparing means for causing said memorizing means to replace the memorized clogging threshold with a new clogging threshold progressively lower than the previously memorized clogging threshold each time a reduction of said clogging level is revealed. The present invention will be more apparent from the description of a preferred embodiment thereof given hereinafter by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 is a simplified block diagram of an apparatus constructed in accordance with the present invention and shown in one example of application; Figure 2 is a flow diagram representing a sequence of operations effected by the apparatus of Figure 1 under the control of a processing unit of the apparatus; Figure 3 shows the relationship between two quantities measured by respective instruments of the apparatus of Figure 1 under different conditions; and Figure 4 shows two examples of the action of the apparatus of Figure 1 under two different operating conditions. In Figure 1, the reference numeral 10 indicates overall an apparatus for controlling the regeneration of two filters 1 and 2 for the particulate present in the exhaust gas of a diesel engine 3. The filters 1 and 2 are substantially connected in parallel and are interposed between an exhaust gas collection pipe 5 disposed immediately downstream of the engine 3 and a venturi device 6 which is connected to a further pipe 7 carrying the exhaust gas. The pipe 5 comprises two branches 11 and 12 which lead respectively to the filters 1 and 2 and into which there are connected solenoid valves 13 and 14 activated in opposition by an an electrical signal reaching a terminal 15 and which, in the case only of the solenoid valve 13, is negated by an inverting gate 16. each filter 1, 2 (consisting for example of a monolithic ceramic element) is provided with a respective burner (with its control system) 21, 22 of conventional type. Each burner 21, 22 is connected both to a first terminal 23, 24 from which it receives a corresponding activation signal, and to a second terminal 25, 26, to which it transmits a corresponding control signal usable to indicate whether the burner and relative control system are active or not. A first pressure difference sensor 31 is installed across the filters 1 and 2, a second pressure difference sensor 32 is installed between the outlets of the filters and the venturi device 6, and a third pressure difference sensor 33 is installed between the inlets to the filters 1 and 2 (upstream of the solenoid valves 13 and 14) and the venturi device 6. The sensors 31, 32, 33 are enclosed, together with a temperature sensor 34, within a container 35 to keep them all at the same temperature (read by the sensor 34). The sensors 31, 32, 33, 34 generate respective signals which are fed to corresponding terminals 41, 42, 43, 44. The apparatus 10 also comprises a processing and computing unit 50 (conveniently provided with a microprocessor) having a plurality of input and output terminals indicated by the same reference numerals as said terminals, to which they are connected in a manner not shown. The unit 50 comprises a further five outputs connected to respective indicator lamps 51, 52, 53, 54, 55 which are activated respectively in the following case: lamp 51: filter 1 connected lamp 52: filter 2 connected lamp 53: filter 1 undergoing regeneration lamp 54: filter 2 undergoing regeneration lamp 55: fault situation. Figure 3 shows the relationship between the pressure difference Δp2 measured across the venturi device 6 and the pressure difference Δp1 measured across the filter 1 or 2, for three different decreasing clogging levels Ia, Ib, Ic of particulate trapped in the filter 1 or 2. In reality, the relationship is not linear as shown in Figure 3, in that the straight line segments shown in this figure are obtained by a multiple linear regression operation on a large number of measurements. It is in any event reasonable to consider that the clogging level of each filter 1 or 2 can be evaluated with good approximation simply by measuring the said values Δp1 and Δp2. Figure 4 shows the variation in clogging with time for two operating conditions. The first condition can be considered as the norm, in that the clogging increases progressively with time to provide a monotone increasing function which intercepts the maximum regeneration threshold Smax at time tr to initiate intentional regeneration at that moment. The second condition involves spontaneous regeneration at time t1 which, as specified hereinafter, results in the exhaust gas flow being switched to the other filter for a time T (which terminates when spontaneous regeneration or intentional regeneration takes place in said other filter), the regeneration threshold being reduced to the value S1 (less than Smax), and subsequent intentional regeneration at time tr1, with reinstatement of the value Smax as regeneration threshold. The operation of the apparatus 10 is described hereinafter in detail with reference to Figure 2. The operation starts with a block 60 which reads the data provided by the sensors, 31, 32, 33, 34, after which comes a comparison block 61 which checks if the temperature T measured by the sensor 34 is greater than a predetermined minimum value Tm. If the result is negative, the procedure returns to the input of block 60 to prevent processing of the data provided by the other sensors, which are not accurate for low temperatures. If the result is positive, the program passes to a comparison block 62, which checks if the absolute value of the subtraction of Δp1 and Δp2 from Δp3 is greater than a small predetermined value indicated by A. If the result is positive, this signifies that the data provided by at least one of the sensors 31, 32, 33, is in error, so that the program passes to a block 63 which indicates a fault in the system and lights the lamp 55. If the result is negative, the program passes to the evaluation of clogging (for example of the filter 1) by block 64. Block 64 and the next block 65 calculate the clogging of the filter 1 at times N-1 and N to provide two values indicated by IN-1 and IN. A block 66 is then reached to check if the last calculated clogging value (IN) is greater than the preceding (IN-1). If the result is positive, this signifies that there has been a further accumulation of particles between the two calculation times, and it is therefore necessary to check whether the maximum clogging value (Smax) has been exceeded, and thus initiate regeneration, or to again execute the clogging calculation as described heretofore. This is done by passing from block 66 to block 67, in which N is put equal to N+1 and setting a counter K to 0, to then pass to a block 68 for comparing IN with Imax, and then to a block 69 for initiating regeneration of the filter 1 (by activating the burner 21 and lighting the indicator lamp 53), or again to the input of block 64. If the result is negative, this signifies that partial spontaneous regeneration of the filter 1 has occurred, and the program passes to a block 70 which sets the counter content K to K+1. Depending on the effective value assumed by the parameter K (variable for example from 1 to n), a plurality of comparison blocks 71, 72, ....79 are traversed to reach a respective command block 81, 82,....89, which progressively lowers the value of the regeneration limit threshold to S1, S2,....Sn respectively. If the value of K is n+1, the program passes directly to a block 90 for initiating regeneration of the filter 1 in the same manner as described with reference to said block 69, to then pass to a block 90a which reinstates Smax as the regeneration threshold value. The program passes from the blocks 81,.....89 and from the block 90a to a block 91, which zeroes the value relative to the clogging of the filter 1. The block 91 is also reached from the block 69 after passing through a block 69a which reinstates Smax as the regeneration threshold. The program passes from block 91 to a block 92, which causes a signal to he fed to the terminal 15 of the unit 50 to switch over the solenoid valves 13, 14 and consequently deviate the exhaust gas from the engine 3 to the filter 2. At this point, a comparison block 93 checks whether the filter 2 is connected and remains in a waiting state passing through a timer block 94 to execute the same check periodically. If the result of the check is negative, the program returns to the input of the computing block 64 to repeat the aforesaid cycle. In a manner not illustrated but parallel to the aforesaid, the unit 50 also checks constantly whether the time period which has passed from the last regeneration command lies between a minimum value and a maximum value, and if it does not the unit provides a fault signal for example to light the indicator lamp 55. The advantages of the method and apparatus of the present invention are apparent from an examination of their characteristics. Firstly, the progressive lowering of the intervention threshold eliminates the problems caused by spontaneous regeneration. Arranging the sensors in the container 35 and enabling the data provided by them to be used only when the temperature reaches an optimum value means that the sensors can be used over that part of their characteristic curve of greatest accuracy, with undoubted advantages from the point of view of most favourable overall management of regeneration. In addition the presence of the third sensor 33 enables any casual or systematic errors in the measurement of the various pressure differences to be identified, so further improving reliability. Connecting the filters 1 and 2 in parallel enables the same sensors and the same venturi device to be used for both, so significantly limiting cost. Finally, checking the time period which has passed since the last regeneration enables operating faults which may have escaped the previous checks to be detected. For example, a too frequent request for regeneration could not be realistic as it is not possible for the particulate to accumulate in the filter in such quantity in a short time. It could instead be the case that the filter is really clogged but the apparatus is unable to detect this because the clogging calculation can give results which are lower than the true results if the engine 3 operates at low r.p.m., the measurement across the venturi device 6 then possibly being in considerable error. Finally, it is apparent that modifications can be made to the aforesaid method and apparatus but without leaving the scope of the claims. For example the engine could be configured with a single particulate filter provided with a by-pass, or could comprise several filters connected in parallel, provided the aforesaid concept is respected.

Claims: A method controlling the regeneration of at least one particulate filter (1, 2) installed in a diesel engine, wherein the level of clogging of said filter (1, 2) caused by progressive accumulation therein of the particulate is periodically calculated, and wherein an intentional regeneration (69, 90) of said filter (1, 2) is caused when said clogging level reaches a predetermined upper clogging limit (68), characterized by periodically comparing (66) the last calculated clogging level with the previous calculated clogging level after said intentional regeneration (69, 90); and defining a new upper clogging limit (81, 89) progressively lower than the previously defined upper clogging limit each time said comparison reveals a reduction of said clogging level (81, 89). A method as claimed in claim 1, characterized by causing another intentional regeneration (90) if a predetermined number (n) of consecutive reductions in said clogging level are revealed in consecutive comparisons (66) after the previous intentional regeneration (69, 90). A method according to claim 2, characterized by restating (69a, 90a) said predetermined upper clogging limit and zeroing (91) said calculated level of clogging after each one of said intentional regenerations (69, 90). A method according to any previous claim, characterized by checking the time interval passed between two consecutive intentional regenerations (69, 90), comparing said time interval with a minimum time threshold and with a maximum time threshold, and providing a fault indication if said time interval does not lies between said time thresholds. A device controlling the regeneration of at least one particulate filter (1, 2) installed in a diesel engine, according to the method of claim 1, comprising means (31, 32, 33) for measuring quantities related to the clogging of said filter (1, 2) by said particulate, means (50) for processing said quantities and calculating the level of clogging of said filter (1, 2) caused by the progressive accumulation of said particulate, means (50) for memorizing a predetermined upper clogging threshold for said filter (1, 2), and regeneration means (21, 22) adapted to be controlled for an intentional regeneration of said filter (1, 2) when said level of clogging exceeds said predetermined clogging threshold, characterized by comparing means (50) for periodically comparing the last clogging level calculated by said processing means with the previous calculated clogging level after said intentional regeneration, and control means (50) responsive to said comparing means for causing said memorizing means to replace the memorized clogging threshold with a new clogging threshold progressively lower than the previously memorized clogging threshold each time a reduction of said clogging level is revealed. A device as claimed in claim 5, characterized in that said control means (50) include counting means for counting the number of consecutive reductions in the counting level which have not resulted from said intentional regeneration, said control means (5) being adapted to control said regeneration means (21, 22) for another intentional regeneration when said number exceeds a predetermined value. A device as in claimed in claim 6, characterized in that said control means (50) upon controlling an intentional regeneration are also adapted to control said memorizing means to restate said predetermined clogging threshold and to cause said processing means to provide a zero value for the clogging measurement subsequent to said intentional regeneration. A device as claimed in any claim from 5 to 7, wherein said measuring means (31, 32, 33) include a first pressure difference sensor (31) connected between an inlet and an outlet of said filter (1, 2), and wherein a venturi device (6) is connected downstream of said filter (1, 2), characterized in that said measuring means (31, 32, 33) include also a second pressure difference sensor (31) connected between said outlet and said venturi device (6) and a third pressure difference sensor (33) connected between said inlet and said venturi device (6) substantially in parallel with said first and second pressure difference sensors (31, 32), said control means (50) being adapted to check whether at least one of the measurements supplied by said sensors (31, 32, 33) is in error and to enable consequently a fault indicator. A device as claimed in claim 8, characterized by container means (35) internally housing said pressure difference sensors (31, 32, 33), a temperature sensor (34) being housed in said container means (35) to sense the temperature thereof, said processing means (50) being connected with said temperature sensor (34) and being adapted for reading the data provided by said pressure difference sensors (31, 31, 33) only if said temperature exceeds a predetermined minimum temperature. A device as claimed in 8 or 9, wherein at least two filters (1 and 2) are installed in parallel in said diesel machine, and wherein individual shutoff means (13, 14) are installed upstream of said filters (1, 2) and are controlled for rendering said filters (1, 2) individually effective, characterized in that said venturi device (6) is connected downstream of both said filters (1, 2), and said measuring means (31, 32, 33) are adapted to measure each time the level of clogging of the filter (1, 2) presently effective, said control means (50) being adapted to switch the operation of said shutoff means (13, 14) to sequentially render said filters (1, 2) upon controlling each one of said intentional regenerations.

Inventors: INCARDONA, MARIO, OPERTI, CLAUDIO
Applicants: IVECO FIAT S.P.A.
Application year: 1989
Main classification: F01N3
IPC codes: F02B3, F01N9, F01N3