JP7255578B2 - Exhaust gas purification system and control method for exhaust gas purification system - Google Patents

Description

The present disclosure relates to an exhaust gas purification system and a control method for the exhaust gas purification system.

2. Description of the Related Art There has been proposed an electric heater that raises the temperature of a filter device that collects particulate matter contained in exhaust gas from an engine (internal combustion engine) (see, for example, Patent Document 1). There has also been proposed an electric heater that raises the temperature of a NOx purification catalyst device that purifies nitrogen oxides contained in exhaust gas (see, for example, Patent Document 2).

Japanese Unexamined Patent Application Publication No. 2005-090450 Japanese Utility Model Laid-Open No. 5-69315

By using two heaters, an electric heater for raising the temperature of the filter device described in Patent Document 1 and an electric heater for raising the temperature of the NOx purification catalyst device described in Patent Document 2, the filter device and the NOx It becomes possible to maintain the temperature of both devices of the purification catalyst device in an optimum state.

However, the electric heater is controlled based on the temperature of the device whose temperature is to be raised. Therefore, depending on the temperature of the device to be heated, the two electric heaters will be driven at the same time, increasing power consumption. This increase in power consumption may affect the driving of other power-driven devices.

Therefore, it is conceivable to limit the amount of electric power that can be used by the two electric heaters. However, in this configuration, when it is desired to preferentially raise the temperature of one of the filter device and the NOx purifying catalyst device, it is necessary to raise the temperature of the device in which the two electric heaters are driven at the same time. The problem arises that the heating is slowed down by power budget limitations.

Thus, even if the device described in Patent Document 1 and the device described in Patent Document 2 are simply used, the temperatures of both the filter device and the NOx purification catalyst device can be adjusted to appropriate states. It is not an effective solution to maintain.

An object of the present disclosure is to provide an exhaust gas purification system and a control method for the exhaust gas purification system that maintains the respective optimum temperatures of the filter device and the NOx purification catalyst device while suppressing the amount of power consumption required to raise the temperature of these devices. That's what it is.

An exhaust purification system according to an aspect of the present invention for achieving the above object comprises a filter device and a NOx purification catalyst device arranged in order from the upstream side in the flow of exhaust gas in an exhaust passage through which the exhaust gas of an internal combustion engine passes; an operating state acquiring device for acquiring an operating state of the internal combustion engine in an exhaust purification system comprising a filter heater for raising the temperature of a filter device and a catalyst heater for raising the temperature of the NOx purification catalyst device; and a control device for controlling the filter heater and the catalyst heater, wherein the control device controls the filter heater driven by the filter heater based on the operating state acquired by the operating state acquisition device. Control for switching between a state in which the priority of temperature control is higher than the priority of catalyst temperature increase control driven by the catalyst heater and a state in which the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control. , and under the condition that both the filter temperature increase control and the catalyst temperature increase control are performed, the control with the higher priority is performed.

Further, a control method for an exhaust gas purification system according to an aspect of the present invention for achieving the above objects includes a filter device and a NOx purification system arranged in an exhaust passage through which exhaust gas of an internal combustion engine passes, in order from the upstream side in the flow of exhaust gas. A control method for an exhaust purification system comprising a catalyst device, a filter heater for raising the temperature of the filter device, and a catalyst heater for raising the temperature of the NOx purification catalyst device, wherein the operating state of the internal combustion engine. a state in which priority of filter temperature increase control driven by the filter heater is higher than priority of catalyst temperature increase control driven by the catalyst heater, based on the acquired operating state; a step of switching to a state in which the priority of catalyst temperature increase control is higher than the priority of said filter temperature increase control; and after performing said switching, performing both said filter temperature increase control and said catalyst temperature increase control. and performing the control with the higher priority under the condition that the control of the above is performed.

According to the present disclosure, the power consumption required to raise the temperature of the filter device and the NOx purification catalyst device is suppressed by raising the temperature of the device whose temperature should be prioritized according to the operating state of the internal combustion engine. while maintaining each of these devices at the optimum temperature.

1 is a diagram illustrating an exhaust purification system according to an embodiment of the invention; FIG. It is a control flow showing control which switches a priority. It is a control flow showing filter temperature raising control. FIG. 4 is a control flow continuing from FIG. 3; FIG. 4 is a control flow showing catalyst temperature increase control;

Hereinafter, an exhaust purification system 1 according to an embodiment of the present disclosure will be described with reference to the drawings.

In the exhaust gas purification system 1 of the present embodiment, as illustrated in FIG. A reduction type catalyst device (NOx purification catalyst device) 6 is arranged.

The engine 2 is a device that generates power by mixed combustion of fresh air and fuel F inside each of a plurality of (four in this embodiment) cylinders 2a. Fuel F is supplied from a fuel injection device 2b arranged inside each cylinder 2a. The power of the engine 2 is mainly used for running the vehicle having the engine 2 therein. The exhaust passage 3 is connected to each cylinder 2a via an exhaust manifold, and is a passage through which exhaust gas G generated by mixed combustion inside each cylinder 2a passes. The exhaust passage 3 communicates with the atmosphere, and the exhaust gas G is discharged to the atmosphere.

The oxidation catalyst device 4 oxidizes hydrocarbons and carbon monoxide contained in the exhaust gas G by the action of an oxidation catalyst carried inside. The filter device 5 collects particulate matter (PM) contained in the exhaust gas G. As shown in FIG. The selective reduction catalyst device 6 reduces NOx contained in the exhaust gas G with ammonia by the action of a selective reduction catalyst (NOx purification catalyst) carried inside. Ammonia is obtained by hydrolyzing the urea water U injected from the urea water injection device 6 a arranged in the exhaust passage 3 upstream of the selective reduction catalyst device 6 with the heat of the exhaust G. Note that, in the present embodiment, the selective reduction catalyst device 6 is an example of a NOx purification catalyst device.

The exhaust purification system 1 includes a filter heater 7 arranged in the exhaust passage 3 between the oxidation catalyst device 4 and the filter device 5, and arranged in the exhaust passage 3 between the filter device 5 and the selective reduction catalyst device 6. Catalyst heater 8 is provided. The filter heater 7 has a function of raising the temperature of the filter device 5 . The catalyst heater 8 has a function of raising the temperature of the selective reduction catalyst device 6 . Both filter heater 7 and catalyst heater 8 are electrically connected to battery 9 . The filter heater 7 and the catalyst heater 8 are composed of on-off electric heaters, and their power consumption during driving is substantially constant. The power consumption of each of the filter heater 7 and the catalyst heater 8 is set according to, for example, the capacity of the battery 9 and the usage status of another generator (not shown) connected to the battery 9 .

Note that the filter heater 7 may be arranged in the exhaust passage 3 on the upstream side of the filter device 5 and on the upstream side of the oxidation catalyst device 4 as long as it can indirectly or directly raise the temperature of the filter device 5 . Alternatively, it may be integrated with the filter device 5 . Similarly, the catalyst heater 8 may also indirectly or directly raise the temperature of the selective reduction catalyst device 6, and may be integrated with the selective reduction catalyst device 6. The exhaust purification system 1 includes a filter A temperature sensor (filter temperature detection device) 10 , a catalyst temperature sensor (catalyst temperature detection device) 11 , and a front-rear differential pressure sensor 12 are provided.

The filter temperature sensor 10 is arranged in the exhaust passage 3 preceding the filter device 5 or inside the filter device 5 to detect the filter temperature Tf of the filter device 5 . The catalyst temperature sensor 11 is arranged in the exhaust passage 3 preceding the selective reduction catalyst device 6 or inside the selective reduction catalyst device 6 to detect the catalyst temperature Tn of the selective reduction catalyst device 6 . The front-rear differential pressure sensor 12 is arranged in the exhaust passage 3 in the vicinity of the filter device 5 and detects the differential pressure of the exhaust gas G passing through the front and back of the filter device 5 .

The exhaust purification system 1 has a control device 13 . The control device 13 is hardware composed of a CPU (Central Processing Unit) that performs various types of information processing, an internal storage device capable of reading and writing programs and information processing results used for performing the various types of information processing, and various interfaces. is. The control device 13 is electrically connected to various sensors 10 to 12, the fuel injection device 2b, the urea water injection device 6a, the filter heater 7, the catalyst heater 8, and the like.

The control device 13 performs regeneration control, filter temperature increase control, catalyst temperature increase control, filter temperature increase control, and catalyst temperature increase control and control for switching the priority.

The regeneration control is control in which the start and end of control are switched based on the differential pressure detected by the front-rear differential pressure sensor 12 . In the regeneration control, unburned fuel is supplied to the oxidation catalyst device 4 by post-injection from the fuel injection device 2b, and the temperature of the exhaust gas G flowing into the filter device 5 is reduced by the oxidation exothermic reaction of the unburned fuel in the oxidation catalyst device 4. This control is to raise the temperature to a temperature at which the particulate matter collected by the filter device 5 can be combusted. 600 degrees is exemplified as a temperature at which particulate matter can be combusted. The regeneration control may be performed by injecting unburned fuel from a passage fuel injection device arranged in the exhaust passage 3 on the upstream side of the oxidation catalyst device 4 instead of the post injection of the fuel injection device 2b.

The filter temperature increase control is control in which the start and end of control are switched by comparing the filter temperature Tf detected by the filter temperature sensor 10 with a preset filter temperature threshold. The filter temperature threshold has a filter upper limit temperature Tfa and a filter lower limit temperature Tfb. The filter temperature increase control is control to drive the filter heater 7 based on the filter temperature Tf to keep the filter temperature Tf within the temperature range between the lower limit filter temperature Tfb and the upper limit filter temperature Tfa.

Further, the filter temperature increase control is control for constantly driving the filter heater 7 when the priority of the filter temperature increase control is higher than the priority of the catalyst temperature increase control. In the present disclosure, "always driving" refers to a state in which the priority of filter temperature increase control is higher than that of catalyst temperature increase control to a state in which the priority of filter temperature increase control is lower than that of catalyst temperature increase control. This means that the driving of the filter heater 7 is continued until switching to .

Each of the filter upper limit temperature Tfa and the filter lower limit temperature Tfb is set in advance by experiments, tests, or simulations. The filter upper limit temperature Tfa is the upper limit of temperature rise of the filter device 5 by driving the filter heater 7 and is proportional to the power consumption of the filter heater 7 . By increasing the power consumption of the filter heater 7, the filter upper limit temperature Tfa can be set to a temperature at which the particulate matter collected by the filter device 5 can be combusted. However, if the filter upper limit temperature Tfa is set to such a temperature, power consumption becomes excessive. Therefore, the filter upper limit temperature Tfa of the present embodiment is set so as to be able to assist the temperature rise in the regeneration control of the filter device 5 and to determine whether the filter device 5 is sufficiently kept warm. In the present disclosure, the ability to assist the temperature rise in regeneration control means that the entire temperature rise of the filter device 5 in the regeneration control is not covered by the oxidation reaction of the unburned fuel in the oxidation catalyst device 4, but the filter upper limit temperature Tfa. Until then, the heating is assisted by the temperature rise by the heater 7 for the filter. In the present disclosure, when the filter device 5 is sufficiently insulated, the low-temperature exhaust G discharged from the engine 2 into the exhaust passage 3 passes through the filter device 5 and flows into the selective catalytic reduction device 6. However, the temperature does not fall below the lower limit temperature Tnb for catalyst, which will be described later. In other words, the temperature of the low-temperature exhaust gas G passing through the filter device 5 is raised by the heat-retained filter device 5, and the temperature of the selective reduction catalyst device 6 can be maintained at or above the lower limit temperature Tnb for the catalyst. The filter lower limit temperature Tfb is set so that it can be determined that the filter device 5 is not kept warm. In the present disclosure, when the filter device 5 is not insulated, the low-temperature exhaust gas G discharged from the engine 2 into the exhaust passage 3 passes through the filter device 5 and flows into the selective catalytic reduction catalyst device 6. It is in a state below the temperature Tnb.

The catalyst temperature increase control is a control in which the start and end of control are switched by comparing the catalyst temperature Tn detected by the catalyst temperature sensor 11 with a preset catalyst temperature threshold value. The catalyst temperature threshold has a catalyst upper limit temperature Tna and a catalyst lower limit temperature Tnb. The catalyst temperature increase control is a control that drives the catalyst heater 8 based on the detected catalyst temperature Tn to keep the catalyst temperature Tn within the temperature range between the catalyst lower limit temperature Tnb and the catalyst upper limit temperature Tna.

Each of the catalyst upper limit temperature Tna and the catalyst lower limit temperature Tnb is set in advance by experiment, test, or simulation based on the activation temperature at which the catalyst of the selective catalytic reduction device 6 is activated. In the present disclosure, the activation temperature is a temperature range in which the catalyst of the selective reduction catalyst device 6 is activated and a desired purification rate is obtained. It is also the temperature zone where it is hydrolyzed to A range of 200 to 300 degrees is exemplified as the activation temperature. In the selective reduction catalyst device 6, there is a temperature higher than the activation temperature at which the purification rate decreases. The catalyst lower limit temperature Tnb is set to a temperature higher than the lower limit of the activation temperature. The catalyst upper limit temperature Tna is set to a temperature higher than the catalyst lower limit temperature Tnb and lower than the temperature at which the purification rate decreases. More preferably, the catalyst upper limit temperature Tna is set to a temperature within the activation temperature range.

The control for switching the priority between the filter temperature increase control and the catalyst temperature increase control is control for switching which of the filter heater 7 and the catalyst heater 8 should be driven based on the operating state of the engine 2 . In the present disclosure, the operating state of the engine 2 includes three states: a cold operating state, a filter regeneration state, and other states. The cold operating state is a state in which the temperature of each part of the engine 2 is equal to or lower than the ambient temperature, and cold start of the engine 2 is exemplified. The filter regeneration state is a state in which regeneration control is performed to burn and remove the particulate matter collected by the filter device 5 . In this embodiment, the operating state of the engine 2 for which the priority is switched is the filter regeneration state and a state other than the filter regeneration state, and the differential pressure sensor 12 is used as the operating state acquisition device. When determining the cold running state, in addition to the above sensors, a sensor capable of determining the cold running state is added. Examples of this sensor include a water temperature sensor that acquires the water temperature of the cooling water of the engine 2 and an oil temperature sensor that acquires the oil temperature of the lubricating oil of the engine 2. It is determined that the vehicle is in the intermittent operation state.

In this switching control, when it is determined that the operating state of the engine 2 is in the filter regeneration state, the priority of the filter temperature increase control is switched to a higher priority than the catalyst temperature increase control. If it is determined to be in a state other than the state, the priority of the catalyst temperature increase control is switched to a state higher than the priority of the filter temperature increase control.

If the priority of the control to be switched is switched and the priority of the filter temperature rise control is higher than the priority of the catalyst temperature rise control, the catalyst temperature rise control will not start while the filter temperature rise control is being performed. It is forbidden. Further, when the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control, the start of the filter temperature increase control is prohibited while the catalyst temperature increase control is being performed. When the priority of the filter temperature increase control is higher than the priority of the catalyst temperature increase control and the filter temperature increase control is not being performed, the prohibition of starting the catalyst temperature increase control is cancelled. Further, when the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control, the prohibition of starting the filter temperature increase control is canceled when the catalyst temperature increase control is not performed.

As illustrated in FIGS. 2 to 5, the control methods of the exhaust purification system 1 of the present embodiment are independent controls, and are repeated at predetermined intervals. It should be noted that the reproduction control is a well-known technique, and the explanation thereof will be omitted.

In this embodiment, flags are used to determine the level of priority and the start and end of each control. Specifically, when the priority of the filter temperature increase control is switched to a higher priority than the catalyst temperature increase control, the first flag F1 is set (F1=1), and the priority of the catalyst temperature increase control is set to the filter The first flag F1 is lowered (F1=0) when the state is switched to a higher priority than the temperature increase control. Further, the second flag F2 is set (F2=1) when the filter temperature increase control is started, and the second flag F2 is cleared (F2=0) when the filter temperature increase control is finished. Further, the third flag F3 is set (F3=1) when the catalyst temperature increase control is started, and the third flag F3 is lowered (F3=0) when the catalyst temperature increase control is finished.

As illustrated in FIG. 2, in the priority switching control, the control device 13 determines whether or not the operating state of the engine 2 is a filter regeneration state in which regeneration control of the filter device 5 is performed (S110). As described above, the regeneration control compares the differential pressure acquired by the differential pressure sensor 12 with a preset differential pressure threshold to determine the start of control. Therefore, in this step as well, when the differential pressure acquired by the differential pressure sensor 12 exceeds a preset differential pressure threshold value, it may be determined that the operating state of the engine 1 is in the filter regeneration state.

When it is determined that the operating state of the engine 1 is in the filter regeneration state (S110: YES), the control device 13 sets the flag F1 and switches to a state in which the priority of the filter temperature increase control is higher than the priority of the catalyst temperature increase control ( S120). On the other hand, when it is determined that the operating state of the engine 1 is in a state other than the filter regeneration state (S110: NO), the control device 13 lowers the flag F1 so that the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control. Switch to high state (S130).

As illustrated in FIG. 3, in the filter temperature increase control, the control device 13 determines whether or not the flag F1 is set, and determines whether the priority of the filter temperature increase control is higher than the priority of the catalyst temperature increase control. (S200).

If it is determined that the flag F1 is set (S200: YES), the controller 13 drives the filter heater 7 to raise the temperature of the filter device 5 (S210). Next, the control device 13 sets the flag F2 to bring the filter temperature increase control into a state (S220). The driving of the filter heater 7 continues as long as the flag F2 is set.

On the other hand, when it is determined that the flag F1 is lowered (S200: NO), the control device 13 determines whether the flag F3 is lowered, and determines whether or not the high-priority catalyst temperature raising control is being performed. (S230). When determining that the flag F3 is down (S230: YES), the control device 13 starts and stops driving the filter heater 7 in the filter temperature increase control.

On the other hand, when determining that the flag F3 is set (S230: NO), the control device 13 prohibits the filter temperature increase control (S240). To prohibit the filter temperature rise control means to stop the drive of the filter heater 7 when it is driven by the filter temperature rise control, and to maintain the stop of the filter heater 7 when the drive of the filter heater 7 is stopped. is. Therefore, when the filter temperature increase control is prohibited, the flag F2 is lowered.

As illustrated in FIG. 4, the filter temperature sensor 10 then obtains the filter temperature Tf (S310). Next, control device 13 determines whether or not filter temperature Tf is lower than filter lower limit temperature Tfb (S320). When it is determined that the filter temperature Tf is lower than the filter lower limit temperature Tfb (S320: YES), the control device 13 drives the filter heater 7 to raise the temperature of the filter device 5 (S330). Next, the control device 13 sets the flag F2 to bring the filter temperature increase control into a state (S330).

On the other hand, when it is determined that the filter temperature Tf is equal to or higher than the filter lower limit temperature Tfb (S320: NO), the control device 13 determines whether the filter temperature Tf is equal to or higher than the filter upper limit temperature Tfa (S350). When it is determined that the filter temperature Tf is equal to or higher than the filter upper limit temperature Tfa (S350: YES), the control device 13 stops driving the filter heater 7 to stop raising the temperature of the filter device 5 (S360). Next, the control device 13 clears the flag F2 to stop the filter temperature increase control (S370).

As illustrated in FIG. 5, in the catalyst temperature increase control, the control device 13 determines whether or not the flag F1 is lowered, and determines whether the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control. (S400).

When determining that the flag F1 is down (S400: YES), the control device 13 starts and stops driving the catalyst heater 8 in the catalyst temperature increase control. On the other hand, if it is determined that the flag F1 is set (S400: NO), the control device 13 determines whether the flag F2 is set or not, and determines whether or not the high-priority filter temperature raising control is being performed. (S410). When determining that the flag F2 is down (S410: YES), the control device 13 starts and stops driving the filter heater 7 in the filter temperature increase control.

On the other hand, if it is determined that the flag F2 is set (S410: NO), the controller 13 prohibits the catalyst temperature increase control (S420). Prohibiting the catalyst temperature increase control means to stop driving the catalyst heater 8 when it is being driven by the catalyst temperature increase control, and to maintain the stop when the catalyst heater 8 is not being driven. is. Therefore, when the catalyst temperature increase control is prohibited, the flag F3 is lowered.

Next, the catalyst temperature sensor 11 acquires the catalyst temperature Tn (S430). Next, control device 13 determines whether or not catalyst temperature Tn is lower than catalyst lower limit temperature Tnb (S440). When it is determined that the catalyst temperature Tn is lower than the catalyst lower limit temperature Tnb (S440: YES), the control device 13 drives the catalyst heater 8 to raise the temperature of the selective reduction catalyst device 6 (S450). Next, the control device 13 sets the flag F3 to bring the catalyst temperature increase control into a state (S460).

On the other hand, when it is determined that the catalyst temperature Tn is equal to or higher than the catalyst lower limit temperature Tnb (S440: NO), the controller 13 determines whether the catalyst temperature Tn is equal to or higher than the catalyst upper limit temperature Tna (S470). When it is determined that the catalyst temperature Tn is equal to or higher than the catalyst upper limit temperature Tna (S470: YES), the controller 13 stops driving the catalyst heater 8 to stop raising the temperature of the selective reduction catalyst device 6 (S480). Next, the control device 13 clears the flag F3 to stop the catalyst temperature increase control (S490).

As described above, according to the exhaust purification system 1 of the present embodiment, the priority of the filter temperature increase control and the catalyst temperature increase control is switched based on the operating state of the engine 2, and the filter temperature increase control and the catalyst temperature increase control are performed. Under the condition that both of the above controls are performed, the control with the higher priority is performed. Therefore, the two heaters are not driven at the same time, and the heater on the side of the device, which should be given priority in increasing the temperature, is preferentially driven. As a result, it is possible to keep these devices 5 and 6 at the optimum temperature while suppressing the power consumption required for raising the temperature of the filter device 5 and the selective catalytic reduction device 6 .

Filter temperature rise control has a role of assisting temperature rise in regeneration control of the filter device 5 and a role of causing the filter device 5 to function as a heat storage material when regeneration control of the filter device 5 is not performed.

When the temperature of the filter device 5 is raised to a temperature at which the collected particulate matter can be combusted only by supplying unburned fuel to the oxidation catalyst device 4 in regeneration control, the fuel consumption increases by the amount of the supplied unburned fuel. Getting worse. Therefore, according to the exhaust purification system 1, when the operating state of the engine 2 is the filter regeneration state, the priority of the filter temperature increase control is switched to a higher priority than the catalyst temperature increase control. Therefore, the temperature rise of the filter device 5 can be assisted by the filter temperature rise control. As a result, the temperature of the filter device 5 can be quickly raised to the temperature required for the regeneration control during the regeneration control of the filter device 5, and the amount of unburned fuel used in the regeneration control can be reduced. As a result, fuel consumption can be improved.

During the regeneration control, that is, when the priority of the filter temperature increase control is higher than that of the catalyst temperature increase control, it is preferable that the filter heater 7 is always driven by the filter temperature increase control. By constantly driving the filter heater 7 during regeneration control, the effect of assisting the temperature rise of the filter device 5 increases, which is advantageous for reducing the amount of unburned fuel used in the regeneration control.

In addition, when the temperature of the filter device 5 is low at times other than regeneration control, the temperature of the selective catalytic reduction catalyst device 6 is lowered when the temperature of the exhaust gas G is lowered. Therefore, according to the exhaust gas purification system 1, when the priority of the catalyst temperature increase control is high, when the catalyst temperature increase control ends, the temperature of the filter device 5 rises even when the regeneration control of the filter device 5 is not performed. When it is low, filter temperature raising control is performed. By performing the filter temperature increase control other than the regeneration control of the filter device 5, the filter device 5 can be made to function as a heat storage material. As a result, when the temperature of the exhaust gas G drops, the temperature of the exhaust gas G that has passed through the filter device 5 can be raised, and the temperature drop of the selective catalytic reduction catalyst device 6 due to the drop in the temperature of the exhaust gas G can be prevented. By avoiding this, the selective reduction catalyst device 6 can be maintained in an activated state.

Catalyst temperature rise control has a role of maintaining the temperature of the selective reduction catalyst device 6 at the activation temperature. When the operating state of the engine 2 is in the cold operating state, both the temperature of the filter device 5 and the temperature of the selective catalytic reduction device 6 are low. Driving two heaters in this state increases power consumption. On the other hand, setting a limit on the amount of power consumption reduces the effect of increasing the temperature of each device. Therefore, according to the exhaust gas purification system 1, when the operating state of the engine 2 is in the cold operating state, the priority of the catalyst temperature increase control is switched to a state higher than the priority of the filter temperature increase control. Therefore, the catalyst temperature increase control can be preferentially performed under the condition that the two heaters are driven. As a result, when the operating state of the engine 2 is in the cold operating state, the temperature of the selective catalytic reduction catalyst device 6 can be quickly increased to the activation temperature.

In this way, filter temperature rise control having a role of assisting the temperature rise in the regeneration control of the filter device 5 and a role of making the filter device 5 function as a heat storage material when the regeneration control of the filter device 5 is not performed, and a selective reduction type Each device can be maintained in an optimum state by selectively using the catalyst temperature increase control, which has a role of maintaining the temperature of the catalyst device 6 at the activation temperature, according to the operating state of the engine 2 .

The filter temperature increase control has a role other than the regeneration control to keep the filter device 5 warm and function as a heat storage material. The situation does not occur all the time. Therefore, by setting the priority of the catalyst temperature increase control higher than the priority of the filter temperature increase control other than the regeneration control, the period during which the temperature of the selective catalytic reduction catalyst device 6 is maintained at the activation temperature or higher becomes longer. , NOx contained in the exhaust gas G can be stably purified by the selective reduction catalyst device 6 .

The catalyst lower limit temperature Tnb is a temperature higher than the lower limit of the temperature at which the catalyst of the selective reduction catalyst device 6 is activated, and the catalyst upper limit temperature Tna is higher than the catalyst lower limit temperature Tnb and within the range of the activation temperature. , the filter lower limit temperature Tfb is higher than the catalyst lower limit temperature Tnb, and the filter upper limit temperature Tfa is higher than the filter lower limit temperature Tfb. Further, the filter upper limit temperature Tfa is preferably set to a temperature higher by 10 to 30° C. than the catalyst upper limit temperature Tna, preferably about 20° C. higher. Further, the filter lower limit temperature Tfb is preferably set to a temperature higher by 10 to 30° C. than the catalyst lower limit temperature Tnb, preferably about 20° C. higher. By setting in this way, it is possible to provide a margin for the temperature of the filter device 5 during heat retention when the temperature of the exhaust gas G drops, which is advantageous for the function of the filter device 5 as a heat storage material.

In filter regeneration control, when the operating state of the engine 2 is in the filter regeneration state and the regeneration control is being performed, the filter heater 7 does not have to be driven all the time. Further, when the capacity of the battery 9 is large and a surplus of electric power is expected, the filter regeneration control is performed when the operating state of the engine 2 is in the filter regeneration state and when the regeneration control is performed, the filter upper limit The temperature Tfa may be brought close to a temperature at which particulate matter can be combusted to enhance the effect of assisting the temperature increase by the filter heater 7 .

1 Exhaust purification system 2 Engine (internal combustion engine)
2a Cylinder 2b Fuel injection device 3 Exhaust passage 4 Oxidation catalyst device 5 Filter device 6 Selective reduction type catalyst device (NOx purification catalyst device)
6a Urea water injection device 7 Filter heater 8 Catalyst heater 9 Battery 10 Filter temperature sensor (filter temperature detection device)
11 catalyst temperature sensor (catalyst temperature detection device)
12 Front-back differential pressure sensor 13 Control device

Claims (9)

A filter device and a NOx purification catalyst device are arranged in an exhaust passage through which exhaust gas of an internal combustion engine passes in order from the upstream side with respect to the flow of exhaust gas, a filter heater for raising the temperature of the filter device, and the NOx purification catalyst device. and a catalyst heater for warming,
An operating state acquisition device that acquires the operating state of the internal combustion engine, and a control device that controls the filter heater and the catalyst heater,
Based on the operating state acquired by the operating state acquisition device, the control device prioritizes the filter temperature increase control driven by the filter heater over the catalyst temperature increase control driven by the catalyst heater. and a state in which the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control, and both the filter temperature increase control and the catalyst temperature increase control are performed. An exhaust gas purification system characterized in that it is configured such that control with a higher priority is performed under conditions where 2. The control device according to claim 1, wherein when the operating state is a cold operating state, the control device performs control to switch the priority of the catalyst temperature increase control to a higher priority than the filter temperature increase control. Exhaust purification system. 3. The control device according to claim 1, wherein when the operating state is the filter regeneration state, the control device performs control to switch the priority of the filter temperature increase control to a higher priority than the catalyst temperature increase control. exhaust purification system. 4. The exhaust gas according to claim 3, wherein the control device switches to a state in which the priority of the catalyst temperature increase control is higher than the priority of the filter temperature increase control when the operating state is a state other than the filter regeneration state. purification system. a filter temperature detection device that detects a filter temperature of the filter device; and a catalyst temperature detection device that detects a catalyst temperature of the NOx purification catalyst device,
The filter temperature increase control is control in which the start and stop of driving the filter heater are switched by comparing the filter temperature detected by the filter temperature detection device with a preset filter temperature threshold,
The catalyst temperature increase control is control for switching between starting and stopping the driving of the catalyst heater by comparing the catalyst temperature detected by the catalyst temperature detection device with a preset catalyst temperature threshold,
In a state in which the priority of either one of the filter temperature increase control and the catalyst temperature increase control is higher than the priority of the other control, the other control is started when the one control is not performed. The exhaust purification system according to any one of claims 1 to 4, wherein the exhaust purification system is enabled. The filter temperature threshold has a filter upper limit temperature and a filter lower limit temperature, the catalyst temperature threshold has a catalyst upper limit temperature and a catalyst lower limit temperature,
The filter temperature increase control starts driving the filter heater when the filter temperature is lower than the filter lower limit temperature, and starts driving the filter heater when the filter temperature exceeds the filter upper limit temperature. is the control to stop,
The catalyst temperature increase control starts driving the catalyst heater when the catalyst temperature is lower than the lower limit temperature for catalyst, and starts driving the heater for catalyst when the catalyst temperature exceeds the upper limit temperature for catalyst. 6. The exhaust purification system according to claim 5, wherein the control is to stop. The catalyst lower limit temperature is a temperature higher than the lower limit temperature at which the catalyst of the NOx purification catalyst device is activated, and the catalyst upper limit temperature is higher than the catalyst lower limit temperature and within the activation temperature range. 7. The exhaust purification system according to claim 6, wherein the filter lower limit temperature is higher than the catalyst lower limit temperature, and the filter upper limit temperature is higher than the filter lower limit temperature. wherein said filter temperature rise control is control for constantly driving said filter heater when said filter temperature rise control has a higher priority than said catalyst temperature rise control. The exhaust purification system according to any one of Claims 1 to 3. A filter device and a NOx purification catalyst device are arranged in an exhaust passage through which exhaust gas of an internal combustion engine passes in order from the upstream side with respect to the flow of exhaust gas, a filter heater for raising the temperature of the filter device, and the NOx purification catalyst device. In a control method for an exhaust gas purification system comprising a catalyst heater for heating,
obtaining an operating state of the internal combustion engine;
A state in which the priority of filter temperature rise control driven by the filter heater is higher than the priority of the catalyst temperature rise control driven by the catalyst heater and the priority of the catalyst temperature rise control based on the acquired operating state. switching to a state where the priority is higher than the priority of the filter temperature rise control;
After performing the switching, performing the control with the higher priority under the condition that both the filter temperature increase control and the catalyst temperature increase control are performed;
A control method for an exhaust purification system, comprising:

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