JP2015094324A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine control device capable of performing the transfer of an engine operation mode from a low NOx mode to a high NOx mode further properly.SOLUTION: On condition that the catalyst temperature of a NOx reduction catalyst device 27 becomes equal to or higher than an activity determination value, an electronic control unit 50 shifts the engine operation mode from a low NOx mode, in which the NOx generation quantity of the engine becomes less, to a high NOx mode, in which the NOx generation quantity becomes more. On the basis of the detection results of the vehicle speed and the ambient temperature, moreover, the electronic control unit 50 sets that activity determination value at a higher value, if the vehicle speed is high or if the ambient temperature is low.

Description

  The present invention relates to an engine control device that switches an engine operation mode between a low NOx mode and a high NOx mode based on a catalyst temperature of a NOx reduction catalyst device.

  The NOx reduction catalyst device exhibits a suitable NOx purification capacity when the catalyst temperature increases until the catalyst is activated. Therefore, for example, as seen in Patent Document 1, when the catalyst temperature is low, the engine is operated in a low NOx mode in which the amount of NOx generated in the engine is small. When the catalyst temperature is high, the amount of NOx generated in the engine is large. An engine control device that operates an engine in a high NOx mode that can improve fuel efficiency and the like is known.

Special table 2010-519459 gazette

  By the way, the engine control device grasps the catalyst temperature by directly measuring it using a temperature sensor (catalyst temperature sensor) installed in the NOx reduction catalyst device or by indirectly obtaining it from the detection result of the exhaust temperature. ing.

  On the other hand, the catalyst temperature of the NOx reduction catalyst device also varies depending on surrounding environmental factors. For example, when the outside air temperature is low, more heat is taken away by the outside air. Further, when the vehicle speed is high, the traveling wind that flows around takes more heat from the NOx reduction catalyst device. Therefore, under such environmental conditions, it is difficult for the catalyst temperature to rise in the portion near the tube wall of the NOx reduction catalyst device, and the catalyst temperature is high in the portion near the center of the NOx reduction catalyst device, but in the portion near the outer wall. The catalyst temperature may still remain low.

  In such a case, even if the catalyst temperature grasped by the engine control device is a temperature sufficient for the activity of the catalyst, the catalyst is only partially activated in the entire NOx reduction catalyst device. Therefore, in the conventional engine control device, depending on the environmental conditions, even when the NOx purification capacity of the NOx reduction catalyst device is not actually sufficiently increased, the engine operation mode may be shifted to the high NOx mode. In some cases, NOx generated in the engine cannot be sufficiently processed.

  The present invention has been made in view of such circumstances, and the problem to be solved is to provide an engine control device that can more accurately perform the transition of the engine operation mode from the low NOx mode to the high NOx mode. There is to do.

  An engine control device that solves the above problem is applied to an engine including a NOx reduction catalyst device that reduces and purifies NOx in exhaust gas, on the condition that the catalyst temperature of the NOx reduction catalyst device is equal to or higher than a threshold value. The engine operation mode is shifted from the low NOx mode in which the amount of generated NOx is smaller to the high NOx mode in which the amount of generated NOx is larger. Then, based on the detection result of at least one of the vehicle speed and the outside air temperature, the threshold value is increased when the vehicle speed is high or when the outside air temperature is low compared to when it is not.

  In the above configuration, when the vehicle temperature is high or the outside air temperature is low and the catalyst temperature in the vicinity of the tube wall of the NOx reduction catalyst device is difficult to rise, only after the catalyst temperature grasped by the engine control device is higher than normal, The engine operation mode is not shifted from the low NOx mode to the high NOx mode. Therefore, the transition to the high NOx mode when the NOx purification capability of the NOx reduction catalyst device is insufficient is preferably suppressed. Therefore, the engine operation mode can be shifted more accurately from the low NOx mode to the high NOx mode.

1 is a schematic diagram schematically showing a configuration of an engine to which an embodiment of an engine control device is applied. The flowchart which shows the process sequence of the operation mode switching routine which the engine control apparatus of the embodiment performs. The graph which shows the relationship between the active determination value set in the same operation mode switching routine, a vehicle speed, and external temperature.

Hereinafter, an embodiment of an engine control device will be described in detail with reference to FIGS. In addition, the engine control apparatus of this embodiment is applied to the vehicle-mounted diesel engine.
As shown in FIG. 1, in an intake passage 10 of an engine to which the control device of the present embodiment is applied, an air cleaner 11 that filters intake air, a compressor 12 of a turbocharger that pressurizes intake air, An intercooler 13 for cooling and an intake throttle valve 14 for adjusting the flow rate of intake air are provided. The intake passage 10 is branched for each cylinder of the engine in an intake manifold 15 provided downstream of the intake throttle valve 14. The intake manifold 15 is provided with an intake air temperature sensor 16 for detecting the intake air temperature.

  On the other hand, the exhaust passage 20 of the engine has an exhaust manifold 21 that joins the exhaust discharged from the cylinders. The exhaust manifold 21 is provided with a fuel addition valve 22 for adding fuel to the exhaust. A turbocharger turbine 23 is installed in the exhaust passage 20 downstream of the exhaust manifold 21.

  A PM filter 24, a urea addition valve 25, an exhaust temperature sensor 26, a NOx reduction catalyst device 27, and an ammonia oxidation catalyst device 28 are installed in that order from the upstream side in the downstream portion of the turbine 23 in the exhaust passage 20. The PM filter 24 collects particulate matter (PM) in the exhaust gas, and the urea addition valve 25 adds urea water into the exhaust gas. The exhaust temperature sensor 26 detects the temperature of the exhaust gas flowing into the NOx reduction catalyst device 27 (incoming gas temperature), and the NOx reduction catalyst device 27 reduces ammonia generated by thermal decomposition and hydrolysis of urea water. Used as an agent to reduce and purify NOx in the exhaust. Further, the ammonia oxidation catalyst device 28 oxidizes and purifies ammonia slipped from the NOx reduction catalyst device 27. The exhaust passage 20 is provided with a differential pressure sensor 29 that detects the differential pressure of the exhaust gas before and after the PM filter 24 and a catalyst temperature sensor 30 that detects the internal temperature (catalyst temperature) of the NOx reduction catalyst device 27. There is also.

  Further, the engine is provided with an EGR passage 40 for recirculating a part of the exhaust gas in the exhaust passage 20 to the intake passage 10. The EGR passage 40 is provided with an EGR cooler 41 for cooling the recirculated exhaust gas (EGR gas), and an EGR valve 42 for adjusting the exhaust gas recirculation amount.

  Such an engine is controlled by an electronic control unit 50. The electronic control unit 50 includes a central processing unit (CPU) that executes various arithmetic processes related to engine control, a read-only memory (ROM) that stores control programs and data, CPU arithmetic results, and sensor detection results. Etc. are provided with a random access memory (RAM) for temporarily storing them. The electronic control unit 50 receives detection signals from various sensors that detect the operating state of the engine, including the intake air temperature sensor 16, the exhaust gas temperature sensor 26, the differential pressure sensor 29, and the catalyst temperature sensor 30 described above. Further, the electronic control unit 50 also receives detection signals from a vehicle speed sensor 51 that detects the vehicle speed and an outside air temperature sensor 52 that detects the outside air temperature.

  The electronic control unit 50 determines the engine control parameters such as the fuel injection amount, the ignition timing, and the throttle opening based on the detection signal of each sensor, and controls the engine operating state. The electronic control unit 50 switches the engine operation mode between the low NOx mode and the high NOx mode during such engine control. In the low NOx mode, the value of each control parameter is determined so that the amount of NOx generated in the engine is smaller. In the high NOx mode, the amount of NOx generated in the engine is larger, but the fuel efficiency is improved and the combustion noise is reduced. The value of each control parameter is determined so as to be a value more suitable for suppression.

  FIG. 2 shows a processing procedure of the electronic control unit 50 for switching the operation mode of the engine. The processing of the operation mode switching routine shown in the figure is executed by the electronic control unit 50 at regular intervals during engine operation.

  When the processing of this routine is started, first, in step S100, the detected value of the vehicle speed by the vehicle speed sensor 51 and the detected value of the outside air temperature by the outside air temperature sensor 52 are read. In subsequent step S101, the value of the activity determination value is set based on the detected values of the vehicle speed and the outside air temperature.

  FIG. 3 shows the relationship between the vehicle speed, the outside air temperature, and the set activity determination value. As shown in the figure, the value of the activity determination value is set to a larger value as the vehicle speed is higher or the outside air temperature is lower. In the present embodiment, the activation determination value corresponds to the threshold value in the transition condition of the engine operation mode from the low NOx mode to the high NOx mode and the catalyst temperature of the NOx reduction catalyst device being equal to or higher than the threshold value. Yes.

  When the value of the activity determination value is set, in step S102, it is determined whether or not the urea water addition to the exhaust by the urea addition valve 25 can be executed. This determination is made based on the input gas temperature detected by the exhaust temperature sensor 26, and it is determined that urea water addition can be executed when the input gas temperature is equal to or higher than a predetermined determination value (urea addition execution determination value). If the input gas temperature is lower than a certain value, the urea water does not sufficiently evaporate in the exhaust gas, and adheres to the exhaust passage 20 to generate deposits. Therefore, when the inlet gas temperature is lower than the urea addition execution determination value, execution of urea water addition is prohibited. Incidentally, the value of the urea addition execution determination value is set to a value larger than the maximum value of the activity determination value set in step S101.

  If it is determined that the addition of urea water is feasible (S102: YES), the process of this routine is terminated after the engine operation mode is set to the high NOx mode in step S103. On the other hand, if it is determined that the addition of urea water is not feasible (S102: NO), the process proceeds to step S104.

  When the process proceeds to step S104, in step S104, it is determined whether or not the catalyst temperature detected by the catalyst temperature sensor 30 is equal to or higher than the activity determination value set in the previous step S101. Here, if the catalyst temperature is lower than the activation determination value (NO), in step S105, the engine operation mode is set to the low NOx mode, and then the processing of this routine is terminated. On the other hand, if the catalyst temperature is equal to or higher than the activity determination value (YES), the process proceeds to step S106.

  When the process proceeds to step S106, in step S106, it is determined whether the ammonia (NH3) adsorption amount of the NOx reduction catalyst device 27 is equal to or greater than a predetermined determination value (non-addition reduction determination value). The ammonia adsorption amount of the NOx reduction catalyst device 27 is obtained by estimation from the urea water addition execution status and the transition of the exhaust temperature so far. Note that the determination here is performed in order to confirm whether or not ammonia sufficient to reduce and purify NOx can be sufficiently adsorbed to the NOx reduction catalyst device 27 without adding urea water.

  Here, if the ammonia adsorption amount is equal to or greater than the non-addition reduction determination value (S106: YES), the process proceeds to step S103, and after the engine operation mode is set to the high NOx mode in step S103, this time This routine is finished. On the other hand, if the ammonia adsorption amount is less than the non-addition reduction determination value (S106: NO), the process proceeds to step S105, and after the engine operation mode is set to the low NOx mode in step S105, this time The processing of this routine is terminated.

Then, the effect | action by the process of the operation mode switching routine demonstrated above is demonstrated.
In the engine to which the control device of the present embodiment is applied, when the catalyst temperature of the NOx reduction catalyst device 27 is low and the catalyst is inactive, the engine is operated in a low NOx mode with a small amount of NOx generation. When the catalyst temperature of the NOx reduction catalyst device 27 increases until the catalyst is sufficiently activated, the engine operation mode is shifted from the low NOx mode to the high NOx mode, and although the amount of NOx generated is large, The engine is operated in a state more suitable for suppressing combustion noise.

  Note that when the outside air temperature is low or the vehicle speed is high, heat is carried away by the outside air, so that the catalyst temperature in the vicinity of the tube wall in the NOx reduction catalyst device 27 is difficult to rise. Therefore, even if the catalyst temperature at the detection position of the catalyst temperature sensor 30 is sufficiently increased, the catalyst temperature in the vicinity of the tube wall in the NOx reduction catalyst device 27 may not reach the activation temperature of the catalyst.

  In this respect, in the present embodiment, when the outside air temperature is low or the vehicle speed is high, the activity determination value is set to a larger value than when it is not. Therefore, under an environmental condition where the catalyst temperature in the vicinity of the pipe wall is difficult to rise, the engine operation mode transitions from the low NOx mode to the high NOx mode until the catalyst temperature detected by the catalyst temperature sensor 30 becomes higher than normal. Will not be done.

  On the other hand, even if the catalyst of the NOx reduction catalyst device 27 is active, the exhaust gas temperature is low, and urea water addition to the exhaust gas may not be executed. In such a case, normally, ammonia serving as a reducing agent cannot be supplied to the NOx reduction catalyst device 27, so that the engine operation mode cannot be shifted to the high NOx mode. However, when a sufficient amount of ammonia supplied by the previous urea water addition remains in the NOx reduction catalyst device 27, if the catalyst is active, even if the urea water addition cannot be performed, the residual It is possible to treat NOx using the ammonia. Therefore, in this embodiment, even when urea water addition cannot be performed, if the NOx reduction catalyst device 27 is activated and the ammonia adsorption amount of the NOx reduction catalyst device 27 is equal to or greater than a certain amount, the low NOx mode is increased. The engine operation mode is shifted to the NOx mode.

According to the engine control apparatus of the present embodiment described above, the following effects can be obtained.
(1) In this embodiment, when the vehicle speed is high or the outside air temperature is low, the activation determination value is set to a larger value than when it is not, and the catalyst temperature is equal to or higher than the activation determination value. The engine operation mode is shifted from the low NOx mode to the high NOx mode as a condition. Therefore, the transition to the high NOx mode when the NOx purification capability of the NOx reduction catalyst device 27 is insufficient is suitably suppressed. Therefore, the transition of the engine operation mode from the low NOx mode to the high NOx mode can be performed more accurately.

  (2) In the present embodiment, even when urea water addition cannot be executed, the low NOx mode is achieved if the catalyst of the NOx reduction catalyst device 27 is active and the ammonia adsorption amount of the NOx reduction catalyst device 27 is equal to or greater than a certain amount. Since the engine operation mode is shifted from the high NOx mode to the high NOx mode, the opportunity for executing the high NOx mode increases.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, when the catalyst of the NOx reduction catalyst device 27 is active and the ammonia adsorption amount of the NOx reduction catalyst device 27 is equal to or greater than a certain amount, the engine operation mode is shifted from the low NOx mode to the high NOx mode. As a result, the number of opportunities for executing the high NOx mode has been increased. However, even if the transition to the high NOx mode in such a situation is not performed, the effect (1) can be obtained by setting the activity determination value based on the vehicle speed and the outside air temperature as described above.

  In the above embodiment, the activity determination value is set based on both the vehicle speed detection value and the outside air temperature detection value. However, the activity determination value is set based only on one of these detection values. May be.

  In the above embodiment, the NOx reduction catalyst device 27 is a catalyst device that reduces and purifies NOx in the exhaust gas using ammonia generated by thermal decomposition and hydrolysis of urea water added to the exhaust gas as a reducing agent. Even in a NOx reduction catalyst device that uses other reducing agents, when the detected value of either the vehicle speed or the outside air temperature is large, if the activity determination value is set to a large value compared to when the detected value is small, it is low. The engine operation mode can be shifted more accurately from the NOx mode to the high NOx mode.

  -The engine control apparatus of the said embodiment can be applied to an engine other than a vehicle-mounted diesel engine in a similar manner or a similar manner.

  DESCRIPTION OF SYMBOLS 10 ... Intake passage, 11 ... Air cleaner, 12 ... Compressor, 13 ... Intercooler, 14 ... Intake throttle valve, 15 ... Intake manifold, 16 ... Intake temperature sensor, 20 ... Exhaust passage, 21 ... Exhaust manifold, 22 ... Fuel addition valve , 23 ... Turbine, 24 ... PM filter, 25 ... Urea addition valve, 26 ... Exhaust temperature sensor, 27 ... NOx reduction catalyst device, 28 ... Ammonia oxidation catalyst device, 29 ... Differential pressure sensor, 30 ... Catalyst temperature sensor, 40 ... EGR passage, 41 ... EGR cooler, 42 ... EGR valve, 50 ... electronic control unit, 51 ... vehicle speed sensor, 52 ... outside air temperature sensor.

Claims (1)

Applied to an engine equipped with a NOx reduction catalyst device that reduces and purifies NOx in the exhaust gas, and assuming that the catalyst temperature of the NOx reduction catalyst device is equal to or higher than a threshold, one of the transition conditions is the amount of NOx generated in the engine In the engine control device for shifting the operation mode of the engine from the low NOx mode in which the amount of NOx is reduced to the high NOx mode in which the amount of generated NOx is larger,
Based on the detection result of at least one of the vehicle speed and the outside air temperature, when the vehicle speed is high or the outside air temperature is low, the threshold value is increased as compared to the case where the vehicle speed is not so.
An engine control device characterized by that.