초록 ▼

The invention relates to a method and device (10) for controlling the injection of reducing agent upstream from a catalyst (4) in an exhaust line (2) from a combustion engine. According to the invention, the injection of reducing agent in the exhaust line is controlled on the basis of result of com

The invention relates to a method and device (10) for controlling the injection of reducing agent upstream from a catalyst (4) in an exhaust line (2) from a combustion engine. According to the invention, the injection of reducing agent in the exhaust line is controlled on the basis of result of comparison between a calculated accumulation actual value (A1) and a calculated accumulation setpoint value (A2). The invention also relates to a computer program comprising program code for implementing said method, a computer program product comprising a medium which is readable by an electronic control unit and has stored on it a computer program intended to cause an electronic control unit to implement said method, and an electronic control unit.

대표청구항 ▼

The invention claimed is: 1. A method for controlling injection of a reducing agent upstream from a catalyst in an exhaust line from a combustion engine, the method comprising: calculating an accumulation actual value (A1) representative of a current accumulation in the catalyst of a reducing subst

The invention claimed is: 1. A method for controlling injection of a reducing agent upstream from a catalyst in an exhaust line from a combustion engine, the method comprising: calculating an accumulation actual value (A1) representative of a current accumulation in the catalyst of a reducing substance forming part of or formed by the reducing agent based on information from a computation model, wherein the model takes into account expected reactions in the catalyst under prevailing operating conditions, and the model continuously determines the current state of the catalyst, calculating an accumulation setpoint value (A2) based on an emission setpoint value (E2) and information from the computation model, wherein the emission setpoint value (E2) is representative of a desired content, in exhaust gases leaving the catalyst, of an exhaust gas substance which, as the exhaust gases pass through the catalyst, is at least partly removed from the exhaust gases by the action of the reducing substance or formed by the action of the reducing substance, and the accumulation setpoint value (A2) is representative of the reducing substance accumulation required in the catalyst under prevailing operating conditions for substantially achieving the emission setpoint value (E2), calculating a limitation factor (fconstrain), wherein the limitation factor has a value which depends on an estimate of the current risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed a predetermined limit value, using the limitation factor in calculating the accumulation setpoint value (A2) in such a way that the accumulation setpoint value (A2) decreases in response to increasing risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value comparing the accumulation actual value (A1) with the accumulation setpoint value (A2), and controlling the injection of reducing agent in the exhaust line based on the comparison between the accumulation actual value (A1) and the accumulation setpoint value (A2). 2. A method according to claim 1, further comprising using the limitation factor (fconstrain) as a multiplication factor in calculating the accumulation setpoint value (A2), wherein the limitation factor is given a value which varies between 0 and 1 depending on the current risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value, and wherein the value of the limitation factor is close to 1 when there is no such risk and close to 0 when such risk is imminent. 3. A method for controlling injection of a reducing agent upstream from a catalyst in an exhaust line from a combustion engine, the method comprising: calculating an accumulation actual value (A1) representative of a current accumulation in the catalyst of a reducing substance forming part of or formed by the reducing agent based on information from a computation model, wherein the model takes into account expected reactions in the catalyst under prevailing operating conditions, and the model continuously determines the current state of the catalyst, calculating an accumulation setpoint value (A2) based on an emission setpoint value (E2) and information from the computation model, wherein the emission setpoint value (E2) is representative of a desired content, in exhaust gases leaving the catalyst, of an exhaust gas substance which, as the exhaust gases pass through the catalyst, is at least partly removed from the exhaust gases by the action of the reducing substance or formed by the action of the reducing substance, and the accumulation setpoint value (A2) is representative of the reducing substance accumulation required in the catalyst under prevailing operating conditions for substantially achieving the emission setpoint value (E2), comparing the accumulation actual value (A1) with the accumulation setpoint value (A2) by supplying the accumulation actual value (A1) and the accumulation setpoint value (A2) to a first comparator, which emits a signal (S1) to a first regulator, wherein the signal (S1) depends on the conformity between the accumulation actual value (A1) and the accumulation setpoint value (A2), controlling the injection of reducing agent in the exhaust line based on the comparison between the accumulation actual value (A1) and the accumulation setpoint value (A2) by emitting a control signal (S2) from the first regulator based on the signal from the comparator for controlling the injection of reducing agent in the exhaust line based on the control signal (S2). 4. A method according to claim 3, further comprising calculating an NOx conversion capacity of the catalyst under prevailing operating conditions based on from the computation model and taking the NOx conversion capacity into account in calculating the accumulation setpoint value (A2). 5. A method according to claim 3, wherein according to the computation model, the catalyst is divided in its longitudinal direction into a multiplicity of segments, and wherein the accumulation actual value (A1) and the accumulation setpoint value (A2) refer respectively to current and required reducing substance accumulation in the segment situated nearest to an inlet end of the catalyst. 6. A method according to claim 3, wherein the emission setpoint value (E2) is calculated on the basis of prevailing operating conditions. 7. A method according to claim 3, further comprising using at least the following parameters in the computation model when generating information for the calculation of the accumulation actual value (A1) and the accumulation setpoint value (A2): exhaust gas temperature (P1) upstream from the catalyst, concentration (P2) of the exhaust gas substance in the exhaust gases upstream from the catalyst, exhaust mass flow (P3) through the catalyst, and an amount (P4) of reducing agent injected. 8. A method according to claim 3, wherein urea or ammonia is used as reducing agent, whereby the reducing substance takes the form of ammonia. 9. A method according to claim 3, wherein the exhaust gas substance takes the form of NOx. 10. A method according to claim 3, wherein continuously determining the current state of the catalyst includes the accumulation of the reducing substance in different parts of the catalyst and the conversion of exhaust gas substance taking place in different parts of the catalyst. 11. A method for controlling injection of a reducing agent upstream from a catalyst in an exhaust line from a combustion engine ,the method comprising: calculating an accumulation actual value (A1) representative of a current accumulation in the catalyst of a reducing substance forming part of or formed by the reducing agent based on information from a computation model, wherein the model takes into account expected reactions in the catalyst under prevailing operating conditions, and the model continuously determines the current state of the catalyst, calculating an accumulation setpoint value (A2) based on an emission setpoint value (E2) and information from the computation model, wherein the emission setpoint value (E2) is representative of a desired content, in exhaust gases leaving the catalyst, of an exhaust gas substance which, as the exhaust gases pass through the catalyst, is at least partly removed from the exhaust gases by the action of the reducing substance or formed by the action of the reducing substance, and the accumulation setpoint value (A2) is representative of the reducing substance accumulation required in the catalyst under prevailing operating conditions for substantially achieving the emission setpoint value (E2), comparing the accumulation actual value (A1) with the accumulation setpoint value (A2), and controlling the injection of reducing agent in the exhaust line based on the comparison between the accumulation actual value (A1) and the accumulation setpoint value (A2) determining an emission actual value (E1) by calculation or measurement, wherein the emission actual value (E1) is representative of the current content of the exhaust gas substance in the exhaust gases leaving the catalyst, comparing the emission actual value (E1) with the emission setpoint value (E2), supplying the emission actual value (E1) and the emission setpoint value (E2) to a second comparator which emits a regulator signal (S3) to a second regulator, wherein the regulator signal (S3) depends on the conformity between the emission actual value (E1) and the emission setpoint value (E2), and emitting a control signal (fSP) from the second regulator based on the signal from the second comparator, wherein the control signal (fSP) affects a calculation of the accumulation setpoint value (A2) and calculating the accumulation setpoint value (A2) on information from the computation model and the conformity between the emission actual value (E1) and the emission setpoint value (E2). 12. A method according to claim 11, wherein the emission actual value (E1) is calculated by means of the computation model or on the basis of information from the computation model. 13. A method for controlling injection of a reducing agent upstream from a catalyst in an exhaust line from a combustion engine, the method comprising: calculating an accumulation actual value (A1) representative of a current accumulation in the catalyst of a reducing substance forming part of or formed by the reducing agent based on information from a computation model, wherein the model takes into account expected reactions in the catalyst under prevailing operating conditions, and the model continuously determines the current state of the catalyst, calculating an accumulation setpoint value (A2) based on an emission setpoint value (E2) and information from the computation model, wherein the emission setpoint value (E2) is representative of a desired content, in exhaust gases leaving the catalyst, of an exhaust gas substance which, as the exhaust gases pass through the catalyst, is at least partly removed from the exhaust gases by the action of the reducing substance or formed by the action of the reducing substance, and the accumulation setpoint value (A2) is representative of the reducing substance accumulation required in the catalyst under prevailing operating conditions for substantially achieving the emission setpoint value (E2), obtaining the accumulation setpoint value (A2) by multiplying a first multiplication factor in the form of a calculated accumulation maximum value (Amax) which is representative of the maximum permissible reducing substance accumulation in the catalyst under prevailing operating conditions, with a second multiplication factor which depends on the conformity between the emission actual value (E1) and the emission setpoint value (E2) comparing the accumulation actual value (A1) with the accumulation setpoint value (A2), and controlling the injection of reducing agent in the exhaust line based on the comparison between the accumulation actual value (A1) and the accumulation setpoint value (A2) determining an emission actual value (E1) by calculation or measurement, wherein the emission actual value (E1) is representative of the current content of the exhaust gas substance in the exhaust gases leaving the catalyst, comparing the emission actual value (E1) with the emission setpoint value (E2), and calculating the accumulation setpoint value (A2) on information from the computation model and the conformity between the emission actual value (E1) and the emission setpoint value (E2). 14. A method according to claim 13, wherein according to the computation model, the catalyst is divided in its longitudinal direction into a multiplicity of segments, and wherein the accumulation maximum value (Amax) refers to the maximum permissible reducing substance accumulation under prevailing operating conditions in the segment situated nearest to an inlet end of the catalyst. 15. A method according to claim 13, further comprising calculating a limitation factor (fconstrain) which has a value which depends on an estimate of the current risk that the reducing substance content in the exhaust gases leaving the catalyst might exceed a predetermined limit value, and taking the limitation factor (fconstrain) into account in calculating the accumulation maximum value (Amax) such that the accumulation maximum value (Amax) decreases in response to increasing risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value. 16. A method according to claim 15, further comprising using the limitation factor (fconstrain) as a multiplication factor in calculating the accumulation maximum value (Amax), wherein the limitation factor is given a value which varies between 0 and 1 depending on the current risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value, and wherein the value of the limitation factor is close to 1 when there is no such risk and close to 0 when such risk is imminent. 17. A method according to claim 13, wherein according to the computation model, dividing the catalyst in its longitudinal direction into a multiplicity of segments, for each of the segments of the computation model, calculating an accumulation value (Ak) and a conversion value (Rmax,k) wherein the accumulation value (Ak) is representative of the maximum permissible reducing substance accumulation in the segment under prevailing operating conditions, and the conversion value (Rmax,k) is representative of the expected conversion of the exhaust gas substance in the segment when the reducing substance accumulation in the segment corresponds to the accumulation value, summing the conversion values (Rmax,k) for the various segments, and converting the resulting sum to a fictitious value for the maximum permissible reducing substance accumulation in the segment situated nearest to the inlet end of the catalyst, wherein the fictitious value constitutes said accumulation maximum value (Amax). 18. A method according to claim 17, further comprising for each of the segments, calculating a limitation factor (fconstrain,k), which has a value which depends on an estimate of the current risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed a predetermined limit value, and taking the limitation factor (fconstrain,k) into account in calculating the conversion values (Rmax,k) such that the conversion values (Rmax,k) decrease in response to increasing risk that the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value. 19. A method according to claim 18, further comprising using the limitation factor (fconstrain,k) as a multiplication factor in calculating the conversion value (Rmax,k), wherein the limitation factor is given a value which varies between 0 and 1 depending on the current risk of the reducing substance content of the exhaust gases leaving the catalyst might exceed the predetermined limit value, wherein the value of the limitation factor is close to 1 when there is no such risk and close to 0 when such risk is imminent. 20. A method according to claim 17, further comprising calculating for each of the segments a value (Rk) for the current conversion of the exhaust gas substance in the segment, calculating a value (Rtot) for the total current conversion of the exhaust gas substance in the catalyst is calculated by summation of the values (Rk) of the various segments, and converting the value (Rtot) for the total current conversion of the exhaust gas substance in the catalyst to a fictitious value of the current reducing substance accumulation in the segment situated nearest to an inlet end of the catalyst, wherein the fictitious value constitutes the accumulation actual value (A1).