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Next, an embodiment of the invention will be described in conjunction with the drawings.
The exhaust gas 7 discharged from each cylinder of the engine 1 is fed via an exhaust manifold 8 to a turbine 2b of the turbocharger 2, the exhaust gas 7 after having driven the turbine 2b being discharged outside via an exhaust pipe 9.
Selective reduction catalyst 10 encased in a casing 11 is incorporated in the exhaust pipe 9 through which exhaust gas 7 flows. The selective reduction catalyst 10 is formed as flow-through type honeycomb structure as shown in
Further, arranged upstream of the casing 11 is an urea-water injection valve 13 with an injection nozzle 12, the injection valve 13 being connected to an urea water tank 14 arranged at an appropriate site via an urea-water supply line 15, so that the urea water (reducing agent) 17 in the tank 14 can be added upstream of the selective reduction catalyst 10 via the injection valve 13 by driving a supply pump 16 incorporated in the supply line 15. Thus, urea-water adding means (reducing-agent adding means) 18 is constituted by the urea-water injection valve 13, urea water tank 14, urea-water supply line 15 and supply pump 16.
The engine 1 is provided with a revolution sensor 19 for detecting revolution of the engine. A revolution signal 19a from the revolution sensor 19 and a load signal 20a from an accelerator sensor 20 (sensor for detecting treadled angle of an accelerator pedal) are inputted into an engine control unit or electric control unit 21 (ECU).
In the ECU 21, a fuel injection signal 22a for commanding fuel injection timing and amount to be injected is outputted to a fuel injection device 22 for injecting fuel to each cylinder of the engine 1, so that appropriate fuel injection control is carried out on the basis of current operation status judged from the above-mentioned revolution and load signals 19a and 20a from the sensors 19 and 20.
More specifically, the fuel injection device 22 comprises a plurality of injectors (not shown) each for each cylinder, an electromagnetic valve in each of the injectors being controlled in its opening by the fuel injection signal 22a so as to appropriately control the fuel injection timing and amount to be injected.
An NOx deputation control device 23 (control device) arranged separately from the ECU 21 outputs a valve-opening command signal 13a to the urea-water injection valve 13, and further outputs a drive command signal 16a to the supply pump 16. Thus, by valve-opening actuation of the injection valve 13, the amount of the urea water 17 to be added is appropriately controlled and, upon such addition of the urea water any required injection pressure is obtained by driving the supply pump 16.
The NOx depuration control device 23 receives from the ECU 21 the revolution and load signals 19a and 20a from the sensors 19 and 20 and, on the basis of current operation status judged from these signals, NOx generation amount is estimated; an amount of urea water 17 to be added commensurate with the estimated NOx generation amount is calculated and addition of such required amount of urea water 17 is carried out.
Inputted to the NOx deputation control device 23 are detection signals 24a and 25a from NOx sensors 24 and 25 arranged respectively on the entry and exit sides of the selective reduction catalyst 10 for detecting NOx concentrations as well as a detection signal 26a from a temperature sensor 26 arranged on the entry side of the catalyst 10; on the basis of these detection signals 24a, 25a and 26a, abnormality where a predetermined temperature or more is attained and a predetermined Nox reduction ratio is not attained is judged and, when such abnormality is judged, the control device outputs a control signal 21a to the ECU 21 so as to command restriction of an amount of fuel to be injected.
More specifically, as shown in
In this respect, ascertainment of temperature at step S2 may not always be carried out by actual measurement through the temperature sensor 26 arranged on the entry side of the selective reduction catalyst 10. For example, the exhaust temperature may be estimated from the operation status on the basis of the sensed engine revolution and load.
When the ECU 21 receives the control signal 21a from the NOx deputation control device 23, it selects a map for fuel injection control with the fuel injection amount being reduced than normal, so that on the basis of this map, a reduced amount of fuel to be injected than usaul is outputted as fuel injection signal 22a to the fuel injection device 22.
In this case, restriction of the fuel injection amount lower than usual must be accompanied by changes of injection timing and pressure to appropriate values (corresponding to the change of the fuel injection amount). Therefore these are also adapted to be changed accordingly.
With the exhaust emission control device thus constructed, NOx concentrations on the entry and exit sides of the selective reduction catalyst 10 are monitored by NOx deputation control device 23 on the basis of the detection signals 24a and 25a from both of the NOx sensors 24 and 25: when no remarkable difference between those on the entry and exit sides of the selective reduction catalyst 10 is ascertained, abnormality as non-attainment of a predetermined Nox reduction ratio is judged, and when such abnormality is judged, the control signal 21a is outputted from the NOx depuration control device 23 to the ECU 21 so as to restrict the amount of fuel to be injected; as a result, an amount of NOx to be generated in the engine 1 is reduced to suppress the increase of NOx emission.
Thus, according to the above-mentioned embodiment, even if the NOx deputation system has malfunction, an amount of fuel to be injected can be restricted to reduce an amount of NOx to be generated in the engine 1 to thereby minimize increase of NOx emission.
It is to be understood that an exhaust emission control device of the invention is not limited to the above-mentioned embodiment and that various changes and modifications may be effected without leaving the gist of the invention. For example, the reducing agent added to the selective reduction catalyst may be diesel oil or the like other than the urea water.
Number | Date | Country | Kind |
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2004-179734 | Jun 2004 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP05/11022 | 6/16/2005 | WO | 00 | 11/28/2006 |