JP2021055565A - Exhaust emission control apparatus for internal combustion engine, and vehicle - Google Patents

Abstract

To provide an exhaust emission control apparatus for an internal combustion engine capable of reducing the amount of NOx to be exhausted when regenerating a PM filter.SOLUTION: The exhaust emission control apparatus includes a first SCR catalyst 41, a PM filter 42, and a second SCR catalyst 43 arranged in an exhaust pipe of the internal combustion engine sequentially from the upstream side to the downstream side. When a PM accumulation amount in the PM filter 42 reaches a preparation starting reference value for the PM filter 42, a control device 100 of the exhaust emission control apparatus achieves a first state to stop the injection operation of a first urea water injection device 50A for supplying urea water to the first SCR catalyst 41 and continue the injection operation of a second urea water injection device 50B for supplying the urea water to the second SCR catalyst 43 if the internal combustion engine 10 is under high load operation, and achieves a second state to stop the injection operation of the second urea water injection device 50B and continue the injection operation of the first urea water injection device 50A if the internal combustion engine 10 is under low load operation.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust gas purification device for an internal combustion engine and a vehicle.

Conventionally, an exhaust gas purification device for an internal combustion engine having a NOx selective reduction catalyst (hereinafter referred to as "SCR catalyst") that selectively reduces NOx in exhaust gas using ammonia (NH _{3) as a reducing agent has been used.} It is known (see, for example, Patent Document 1).

In this type of exhaust purification device, ammonia is generated by hydrolyzing the urea water injected into the exhaust pipe from the urea water injection device, and ammonia and NOx are reacted in the SCR catalyst to convert NOx to nitrogen. And water.

In recent years, in this type of exhaust purification device, in order to further improve exhaust emissions, an upstream SCR catalyst, a particulate filter (hereinafter referred to as "PM filter"), from the upstream side to the downstream side, have been introduced into the exhaust pipe. Further, a configuration in which the downstream SCR catalysts are provided in order is being studied.

JP-A-2018-909581

By the way, conventionally, in this type of exhaust gas purification device, a process of periodically burning and removing PM (Particulate Matter) accumulated in the PM filter (hereinafter, referred to as "regeneration of PM filter") is performed. In the regeneration of this PM filter, normally, the engine is operated in the exhaust gas temperature raising mode to raise the exhaust gas temperature, thereby burning and removing the PM accumulated in the PM filter.

Further, conventionally, in this type of exhaust gas purification device, before executing the regeneration of the PM filter, the urea water injection by the urea water injection device is stopped (or the state is limited to only a small amount of protection injection). After waiting for a certain period of time and reducing the amount of ammonia storage of the SCR catalyst (meaning the amount of ammonia adsorbed on the SCR catalyst; the same applies hereinafter), the regeneration of the PM filter (that is, the engine is operated in the exhaust gas temperature raising mode) is started. Control is being performed. The reason for performing such control is to prevent the ammonia in the SCR catalyst from leaving and flowing out to the outside due to the high temperature of the exhaust gas during regeneration of the PM filter.

However, in the exhaust gas purification device provided with the two SCR catalysts, as in the conventional case, the upstream urea water injection device that supplies urea water to the upstream SCR catalyst and the downstream SCR before starting the regeneration of the PM filter. If a standby time is provided in a state where both injection operations of the downstream urea water injection device that supplies urea water to the catalyst are stopped, there is a problem that the standby time becomes long. The reason for this is that most of the NOx discharged from the engine is reduced and purified by the upstream SCR catalyst, and the decrease in the ammonia storage amount of the downstream SCR catalyst is delayed until the ammonia storage amount of the upstream SCR catalyst decreases. This is because it does not proceed as a whole (described later with reference to FIG. 6).

Since the SCR catalyst cannot exhibit sufficient NOx purification performance when the amount of ammonia storage is reduced, exhaust gas purification is performed during the waiting time until the amount of ammonia storage of the downstream SCR catalyst is reduced. The NOx purification rate of the entire device will also decrease. As a result, a large amount of NOx may be discharged to the outside air during a long standby time.

The present disclosure has been made in view of the above problems, and is to provide an exhaust gas purification device for an internal combustion engine capable of reducing the amount of NOx emitted when the PM filter is regenerated, and a vehicle.

The main disclosure that solves the above-mentioned problems is
A first SCR catalyst, a PM filter, and a second SCR catalyst arranged in order from the upstream side to the downstream side in the exhaust pipe of the internal combustion engine.
A first urea water injection device that injects urea water on the upstream side of the first SCR catalyst in the exhaust pipe,
A second urea water injection device that injects urea water between the second SCR catalyst and the PM filter in the exhaust pipe, and a second urea water injection device.
A control device that controls each of the first and second urea water injection devices and also controls the regeneration timing of the PM filter.
With
When the amount of PM deposited in the PM filter reaches a preparation start reference value smaller than the regeneration start reference value of the PM filter, the control device is used.
When the internal combustion engine is in high-load operation, the PM filter is in the first state in which the injection operation by the first urea water injection device is stopped and the injection operation by the second urea water injection device is continued. Wait until the PM accumulation amount in the medium reaches the regeneration start reference value.
When the internal combustion engine is in low load operation, the PM filter is in a second state in which the injection operation by the second urea water injection device is stopped and the injection operation by the first urea water injection device is continued. Wait until the PM accumulation amount in the medium reaches the regeneration start reference value.
It is an exhaust gas purification device.

Also, in other aspects,
It is a vehicle equipped with the above exhaust purification device.

According to the exhaust gas purification device according to the present disclosure, it is possible to reduce the amount of NOx emitted when the PM filter is regenerated.

The figure which shows an example of the structure of the exhaust gas purification apparatus which concerns on one Embodiment. The figure which shows an example of the structure of the 1st injection control part which concerns on one Embodiment The figure which shows an example of the structure of the 2nd injection control part which concerns on one Embodiment A flowchart showing an example of the operation of the filter reproduction control unit according to the embodiment. The figure which shows an example of the relationship between the amount of PM accumulation in a PM filter, and the preparation period for purging ammonia in a 2nd SCR catalyst in the exhaust gas purification apparatus which concerns on one Embodiment. The figure which shows an example of the behavior of the ammonia storage amount of the 1st SCR catalyst and the 2nd SCR catalyst in the preparatory period before the start of regeneration in the exhaust purification apparatus which concerns on one Embodiment. The figure which shows an example of the behavior of the ammonia storage amount of the 1st SCR catalyst and the 2nd SCR catalyst in the preparatory period before the start of regeneration in the exhaust purification apparatus which concerns on one Embodiment. Diagram showing an example of the behavior of the ammonia storage amount of the first SCR catalyst and the second SCR catalyst in the prior art Diagram showing an example of the behavior of the apparatus.

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same function are designated by the same reference numerals, so that duplicate description will be omitted.

[Configuration of exhaust purification device]
Hereinafter, the configuration of the exhaust gas purification device according to the embodiment will be described with reference to FIG.

In the present embodiment, as an example, an embodiment in which the exhaust gas purification device is applied to a diesel engine will be described. However, the exhaust gas purification device according to the present embodiment can be applied not only to a diesel engine but also to a gasoline engine.

FIG. 1 is a diagram showing an example of the configuration of the exhaust gas purification device U according to the present embodiment.

The exhaust gas purification device U according to the present embodiment is mounted on a vehicle such as a truck, and purifies NOx in the exhaust gas of the engine 10.

The engine 10 includes, for example, a combustion chamber, a fuel injection device that injects fuel in the combustion chamber, and the like (not shown). The engine 10 generates power by burning and expanding a mixture of fuel and air in a combustion chamber. The engine 10 is connected to an intake pipe 20 that introduces air into the combustion chamber and an exhaust pipe 30 that discharges the exhaust gas after combustion discharged from the combustion chamber to the outside of the vehicle.

The exhaust gas purification device U includes a first SCR catalyst 41, a PM filter 42, a second SCR catalyst 43, a first urea water injection device 50A, a second urea water injection device 50B, various sensors 61 to 66, and an ECU (Electronic Control Unit). It has 100.

In the exhaust pipe 30, the urea water addition valve 51A of the first urea water injection device 50A, the first SCR catalyst 41, the PM filter 42, and the urea water addition of the second urea water injection device 50B are added from the upstream side to the downstream side. The valve 51B and the second SCR catalyst 43 are arranged in this order.

The PM filter 42 is arranged in the exhaust pipe 30 and captures PM contained in the exhaust gas. The PM filter 42 is composed of, for example, a porous ceramic of cordierite or silicon carbide, and has a honeycomb structure in which inlets and outlets are alternately sealed so that exhaust gas passes through a collection wall formed of the porous ceramic. It is presented. The exhaust gas discharged from the engine 10 flows downstream while passing through the porous collection wall of the PM filter 42, and PM is collected by the collection wall during that time.

The PM filter 42 is supported by an oxidation catalyst that oxidizes the unburned fuel (HC) discharged from the engine 10 and raises the exhaust gas temperature to a desired level (for example, about 600 degrees) for burning PM. ing. The oxidation catalyst may be supported and disposed on the upstream side of the PM filter 42 on a carrier separate from the PM filter 42.

The first SCR catalyst 41 adsorbs hydrolyzed ammonia from the urea water injected from the first urea water injection device 50A, and selectively reduces and purifies NOx in the exhaust gas by the adsorbed ammonia. The first SCR catalyst 41 is arranged on the upstream side of the PM filter 42, for example, directly below the engine 10. As a result, the first SCR catalyst 41 is easily affected by the temperature of the exhaust gas discharged from the engine 10, and the odor can be activated at an early stage immediately after the engine 10 is started.

The second SCR catalyst 43 adsorbs hydrolyzed ammonia from the urea water injected from the second urea water injection device 50B, and selectively reduces and purifies NOx in the exhaust gas by the adsorbed ammonia. The second SCR catalyst 41 is arranged on the downstream side of the PM filter 42.

As the first SCR catalyst 41 and the second SCR catalyst 43, known SCR catalysts can be used. For example, one in which a NOx reduction catalyst such as Fe zeolite, Cu zeolite or vanadium is supported on the surface of a ceramic carrier is used. Can be used. As the first SCR catalyst 41 and the second SCR catalyst 43, those of a type that converts urea water into ammonia on the catalyst may be used.

The first urea water injection device 50A injects urea water on the upstream side of the first SCR catalyst 41 in the exhaust pipe 30. The first urea water injection device 50A includes, for example, a urea water addition valve 51A, a urea water tank 52A, and a supply pump 53A.

In the first urea water injection device 50A, the urea water pumped from the urea water tank 52A by the supply pump 53A is injected from the urea water addition valve 51A into the exhaust pipe 30. The urea water injected into the exhaust pipe 30 from the urea water addition valve 51A is hydrolyzed by the high temperature of the exhaust gas, converted into ammonia, and supplied to the first SCR catalyst 41. Then, the ammonia is adsorbed on the first SCR catalyst 41 and reacts with NOx by the action of the first SCR catalyst 41 to reduce and purify NOx.

The amount of urea water injected from the first urea water injection device 50A to the exhaust pipe 30 is adjusted by adjusting the opening degree of the urea water addition valve 51A. The opening degree of the urea water addition valve 51A is controlled by a control signal output from the ECU 100 (first injection control unit 101).

The second urea water injection device 50B injects urea water on the upstream side of the second SCR catalyst 43 in the exhaust pipe 30. The second urea water injection device 50B has, for example, the same configuration as the first urea water injection device 50A, and includes a urea water addition valve 51B, a urea water tank 52B, and a supply pump 53B. The amount of urea water injected from the second urea water injection device 50B to the exhaust pipe 30 is adjusted by adjusting the opening degree of the urea water addition valve 51B. The opening degree of the urea water addition valve 51B is controlled by a control signal output from the ECU 100 (second injection control unit 102).

The various sensors 61 to 66 are provided to detect the state of the exhaust gas passing through the exhaust pipe 30, the state of the PM filter 42, the state of the first SCR catalyst 41, the state of the second SCR catalyst 43, and the like. Specifically, the exhaust pipe 30 is provided with a first NOx sensor 61, a second NOx sensor 62, a first temperature sensor 63, and a second temperature sensor 64, and the intake pipe 20 is provided with a flow rate sensor 65. There is.

The first NOx sensor 61 is arranged on the upstream side of the first SCR catalyst 41 in the exhaust pipe 30, for example, and detects the amount of NOx (that is, the NOx concentration) flowing into the first SCR catalyst 41. The second NOx sensor 62 is arranged between the second SCR catalyst 43 and the PM filter 42 in the exhaust pipe 30, for example, and detects the amount of NOx flowing into the second SCR catalyst 43.

The first temperature sensor 63 is arranged near the upstream end of the first SCR catalyst 41, for example, and detects the catalyst temperature of the first SCR catalyst 41. The second temperature sensor 64 is arranged near the upstream end of the second SCR catalyst 43, for example, and detects the catalyst temperature of the second SCR catalyst 43.

The flow rate sensor 65 detects, for example, the flow rate of the air flowing into the engine 10. The exhaust gas flow rate is generally obtained by the sum of the intake air amount indicated by the flow rate sensor 65 and that of the engine 10.

For example, one end of the differential pressure sensor 66 is arranged in the exhaust pipe 30 on the upstream side of the PM filter 42, and the other end is arranged in the exhaust pipe 30 on the downstream side of the PM filter 42. The differential pressure between the exhaust pressure on the side and the exhaust pressure on the downstream side (hereinafter, referred to as "front-rear differential pressure of the PM filter 42") is detected.

These various sensors 61 to 66 sequentially transmit the sensor information obtained by the detection to the ECU 100.

The ECU 100 (corresponding to the "control device" of the present invention) controls the operation of the exhaust gas purification device U. The ECU 100 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. Each function described later in the ECU 100 is realized, for example, by the CPU referring to a control program or various data stored in a ROM, RAM, or the like. However, it goes without saying that the function is not limited to processing by software, but can also be realized by a dedicated hardware circuit.

The ECU 100 communicates with the engine 10, the first urea water injection device 50A, the second urea water injection device 50B, and the like to control them and acquire their state information. Further, the ECU 100 acquires sensor information from various sensors 61 to 66, and the state of the exhaust gas passing through the exhaust pipe 30, the state of the PM filter 42, the state of the first SCR catalyst 41, the state of the second SCR catalyst 43, and the like. Is detected.

[Ignition configuration]
The ECU 100 includes a first injection control unit 101, a second injection control unit 102, and a filter regeneration control unit 103.

<About the first injection control unit 101>
The first injection control unit 101 controls the urea water injection from the first urea water injection device 50A by outputting an opening command signal to the urea water addition valve 51A of the first urea water injection device 50A. At this time, the first injection control unit 101 controls, for example, the urea water injection amount of the urea water injection device 50 so that the ammonia storage amount of the first SCR catalyst 41 becomes a predetermined amount. As a result, the first SCR catalyst 41 is maintained in a state where the NOx purification rate is high.

FIG. 2A is a diagram showing an example of the configuration of the first injection control unit 101.

The first injection control unit 101 includes, for example, a target ammonia storage amount setting unit 101a, an actual ammonia storage amount calculation unit 101b, and an injection amount determination unit 101c.

The target ammonia storage amount setting unit 101a sets a target value of the ammonia storage amount in the first SCR catalyst 41. The target value of the ammonia storage amount in the first SCR catalyst 41 is set to, for example, about 100% of the storable amount in the first SCR catalyst 41. However, since the storable amount of the first SCR catalyst 41 changes depending on the catalyst temperature of the first SCR catalyst 41, the target ammonia storage amount setting unit 101a according to the present embodiment is the first SCR indicated by the first temperature sensor 63. Based on the catalyst temperature of the catalyst 41, the target value of the amount of ammonia storage in the first SCR catalyst 41 is set.

In general, the storable amount of the SCR catalyst increases as the catalyst temperature decreases. In particular, when the catalyst temperature exceeds a certain temperature, the storable amount of the SCR catalyst becomes small due to slip (desorption) from the SCR catalyst. The NOx purification rate of the SCR catalyst generally increases as the amount of ammonia storage of the SCR catalyst increases.

The actual ammonia storage amount calculation unit 101b estimates the actual value of the ammonia storage amount of the first SCR catalyst 41 at the present time. The actual ammonia storage amount calculation unit 101b calculates, for example, the adsorption amount of ammonia newly adsorbed on the first SCR catalyst 41 based on the urea water injection amount of the first urea water injection device 50A. Then, the actual ammonia storage amount calculation unit 101b subtracts the consumption amount of ammonia consumed in the first SCR catalyst 41 from the adsorption amount of ammonia newly adsorbed on the first SCR catalyst 41, thereby causing the first SCR catalyst 41 at the present time. Estimate the amount of ammonia storage in. That is, the actual ammonia storage amount calculation unit 101b stores in the storage unit (for example, RAM) based on the transition of the urea water injection amount of the first urea water injection device 50A and the transition of the ammonia consumption amount in the first SCR catalyst 41. The current amount of ammonia storage will be updated sequentially.

The amount of ammonia consumed in the first SCR catalyst 41 is estimated from, for example, the NOx concentration indicated by the first NOx sensor 61 and the exhaust gas flow rate indicated by the flow sensor 65 (that is, the total value of the intake air amount and the fuel injection amount). It is calculated based on the amount of NOx reaching the first SCR catalyst 41.

The injection amount determination unit 101c calculates, for example, the difference between the actual value and the target value of the ammonia storage amount in the first SCR catalyst 41 at the present time, and based on the difference, determines the urea water injection amount of the first urea water injection device 50A. decide. The injection amount determination unit 101c uses, for example, a control map in which the difference between the actual value and the target value of the ammonia storage amount in the first SCR catalyst 41 at the present time and the urea water injection amount are associated with the first urea water injection. The urea water injection amount of the device 50A is determined. Then, the injection amount determination unit 101c outputs an opening command signal to the urea water addition valve 51A of the first urea water injection device 50A so that the urea water injection amount is determined by itself.

The configuration in which the first injection control unit 101 controls the urea water injection amount of the first urea water injection device 50A is not limited to the above configuration. The first injection control unit 101 estimates, for example, the amount of NOx corresponding to the amount of NOx arriving at the first SCR catalyst 41 based on the operating state of the engine 10, and determines the amount of urea water injected by the first urea water injection device 50A. It may be controlled.

However, the first injection control unit 101 is configured to be able to stop the injection operation of the first urea water injection device 50A based on the command from the filter regeneration control unit 103. Here, the state in which the injection operation of the first urea water injection device 50A is stopped includes a state in which only a small amount of protection injection is executed (the same applies hereinafter).

<About the second injection control unit 102>
The second injection control unit 102 controls the urea water injection from the second urea water injection device 50B by outputting an opening command signal to the urea water addition valve 51B of the second urea water injection device 50B. At this time, the second injection control unit 102 controls the urea water injection amount of the second urea water injection device 50B so that the amount of ammonia storage adsorbed on the second SCR catalyst 43 becomes a predetermined amount, for example. As a result, the second SCR catalyst 43 is maintained in a state where the NOx purification rate is high.

FIG. 2B is a diagram showing an example of the configuration of the second injection control unit 102.

The second injection control unit 102 has, for example, a target ammonia storage amount setting unit 102a, an actual ammonia storage amount calculation unit 102b, and an injection amount determination unit 102c. In the present embodiment, the target ammonia storage amount setting unit 102a, the actual ammonia storage amount calculation unit 102b, and the injection amount determination unit 102c of the second injection control unit 102 are each the target ammonia storage of the first injection control unit 101. It has the same configuration as the amount setting unit 101a, the actual ammonia storage amount calculation unit 101b, and the injection amount determination unit 101c.

The target ammonia storage amount setting unit 102a sets a target value of the ammonia storage amount in the second SCR catalyst 43. The target value of the ammonia storage amount in the second SCR catalyst 43 is set to, for example, approximately 100% of the storable amount in the second SCR catalyst 43. However, since the storable amount of the second SCR catalyst 43 changes depending on the catalyst temperature, the target ammonia storage amount setting unit 102a according to the present embodiment determines the catalyst temperature of the second SCR catalyst 43 indicated by the second temperature sensor 64. Based on the above, the target value of the amount of ammonia storage in the second SCR catalyst 43 is set.

The actual ammonia storage amount calculation unit 102b estimates the actual value of the ammonia storage amount of the second SCR catalyst 43 at the present time. The actual ammonia storage amount calculation unit 102b calculates, for example, the adsorption amount of ammonia newly adsorbed on the second SCR catalyst 43 based on the urea water injection amount of the second urea water injection device 50B. Then, the actual ammonia storage amount calculation unit 102b subtracts the consumption amount of ammonia consumed in the second SCR catalyst 43 from the adsorption amount of ammonia newly adsorbed on the second SCR catalyst 43, thereby causing the second SCR catalyst 43 at the present time. Estimate the amount of ammonia storage in. That is, the actual ammonia storage amount calculation unit 102b stores in the storage unit (for example, RAM) based on the transition of the urea water injection amount of the second urea water injection device 50B and the transition of the ammonia consumption amount in the second SCR catalyst 43. The current amount of ammonia storage will be updated sequentially.

The amount of ammonia consumed in the second SCR catalyst 43 is estimated from, for example, the NOx concentration indicated by the second NOx sensor 62 and the exhaust gas flow rate indicated by the flow sensor 65 (that is, the total value of the intake air amount and the fuel injection amount). It is calculated based on the amount of NOx reaching the second SCR catalyst 43.

The injection amount determination unit 102c calculates, for example, the difference between the actual value and the target value of the ammonia storage amount in the second SCR catalyst 43 at the present time, and based on the difference, determines the urea water injection amount of the second urea water injection device 50B. decide. The injection amount determination unit 102c uses, for example, a control map in which the difference between the actual value and the target value of the ammonia storage amount in the second SCR catalyst 43 at the present time and the urea water injection amount are associated with each other to inject the second urea water. The urea water injection amount of the device 50B is determined. Then, the injection amount determination unit 102c outputs an opening command signal to the urea water addition valve 51B of the second urea water injection device 50B so that the urea water injection amount is determined by itself.

The configuration in which the second injection control unit 102 controls the urea water injection amount of the second urea water injection device 50B is not limited to the above configuration. The second injection control unit 102 estimates, for example, the amount of NOx corresponding to the amount of NOx arriving at the second SCR catalyst 43 based on the operating state of the engine 10, and determines the amount of urea water injected by the second urea water injection device 50B. It may be controlled.

However, the second injection control unit 102 is configured to be able to stop the injection operation of the second urea water injection device 50B based on the command from the filter regeneration control unit 103. Here, the state in which the injection operation of the second urea water injection device 50B is stopped includes a state in which only a small amount of protection injection is executed (the same applies hereinafter).

<About filter playback control unit 103>
The filter regeneration control unit 103 monitors the amount of PM deposited on the PM filter 42, prepares the PM filter 42 before regeneration based on the amount of PM deposit, and executes the regeneration of the PM filter 42. ..

For example, the filter regeneration control unit 103 calculates the pressure loss due to PM deposited in the PM filter 42 from the front-rear differential pressure of the PM filter 42 indicated by the differential pressure sensor 66, and thereby the amount of PM deposited in the PM filter 42. To estimate. Then, when the amount of PM deposited in the PM filter 42 becomes equal to or greater than the regeneration start reference value, the filter regeneration control unit 103 executes regeneration of the PM filter 42.

When the PM filter 42 is regenerated, the filter regeneration control unit 103 outputs a control signal to the engine 10, for example, to operate the engine 10 in the exhaust gas temperature rising mode. In the exhaust gas temperature raising mode, the engine 10 raises the exhaust gas to about 500 ° C. by, for example, increasing the fuel injection amount injected from the injector or executing multi-injection. Further, as a method for the engine 10 to raise the temperature of the exhaust gas, a method for increasing the EGR amount of the engine 10 or the like is also used.

However, when the filter regeneration control unit 103 regenerates the PM filter 42, the filter regeneration control unit 103 prevents the ammonia in the second SCR catalyst 43 from being separated and discharged to the outside air as the exhaust gas temperature rises. Before the start of regeneration of the PM filter 42 (that is, before operating the engine 10 in the exhaust gas temperature raising mode), the first urea water injection device 50A and the second urea water injection device 50A and the second are performed so that the ammonia in the second SCR catalyst 43 is purged. Controls the injection operation of the urea water injection device 50B.

FIG. 3 is a flowchart showing an example of the operation of the filter reproduction control unit 103 according to the present embodiment. The flowchart of FIG. 3 is a process in which the filter reproduction control unit 103 repeatedly executes the filter reproduction control unit 103 at predetermined intervals (for example, 100 ms intervals) according to a computer program.

FIG. 4 is a diagram showing an example of the relationship between the amount of PM deposited in the PM filter 42 and the preparation period for purging ammonia in the second SCR catalyst 43 in the exhaust gas purification device U according to the present embodiment.

5A and 5B are diagrams showing an example of the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 in the preparatory period before the start of regeneration in the PM filter 42. FIG. 5A shows the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 when the engine 10 is in low load operation when the PM accumulation amount in the PM filter 42 reaches the preparation start reference value. Shown. FIG. 5B shows the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 when the engine 10 is in high load operation when the PM accumulation amount in the PM filter 42 reaches the preparation start reference value. Shown.

FIG. 6 is a diagram showing an example of the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 in the prior art.

In addition, in FIG. 4, FIG. 5A, FIG. 5B, and FIG. 6, T1 is a timing for stopping the injection operation in either the first urea water injection device 50A or the second urea water injection device 50B (the filter regeneration control unit 103 adjusts period). , T2 represents the timing to stop the injection operation in both the first urea water injection device 50A and the second urea water injection device 50B, and T3 represents the timing to start the regeneration of the PM filter 42.

In the prior art, the first urea water injection device 50A and the first urea water injection device 50A until the PM deposition amount in the PM filter 42 reaches the regeneration start reference value (for example, 100% with respect to the depositable amount of the PM filter 42). Both of the 2-urea water injection device 50B are operated normally. Then, when the amount of PM accumulated in the PM filter 42 reaches the regeneration start reference value, the operations of both the first urea water injection device 50A and the second urea water injection device 50B are stopped, and the second SCR catalyst 43 is stopped. Waits until the amount of ammonia storage in the second SCR catalyst 43 becomes close to 0%, and then the regeneration of the PM filter 42 starts (that is, the engine 10 is operated in the exhaust gas temperature rise mode). Let).

However, depending on the control of the prior art, as shown in FIG. 6, after stopping the operation of both the first urea water injection device 50A and the second urea water injection device 50B, the amount of ammonia storage of the second SCR catalyst 43 increases. It takes a long time to decrease to around 0%. This is because, as described above, under the control of the prior art, NOx in the exhaust gas discharged from the engine 10 after stopping the operation of the first urea water injection device 50A and the second urea water injection device 50B is the first. This is because the reduction rate of the ammonia storage amount of the second SCR catalyst 43 is extremely slow because it is consumed by the 1SCR catalyst 41. Therefore, depending on the control of the prior art, a large amount of NOx is discharged to the outside air not only at the start of reproduction of the PM filter 42 but also before the start of reproduction of the PM filter 42. In addition, delaying the start of reproduction of the PM filter 42 increases the risk of PM being overcollected in the PM filter 42 and causing filter damage.

Therefore, the filter regeneration control unit 103 reduces the amount of ammonia storage of the first SCR catalyst 41 or the second SCR catalyst 43 in advance in order to minimize the NOx emission amount in the preparation period before the start of regeneration of the PM filter 42. An adjustment period (between T1-T2 in FIGS. 4, 5A and 5B) is provided.

Specifically, in the filter regeneration control unit 103, when the amount of PM accumulated in the PM filter 42 reaches the preparation start reference value that is somewhat smaller than the regeneration start reference value of the PM filter 42, the engine 10 is in high load operation. In the case of, the first state is in which the injection operation by the first urea water injection device 50A is stopped and the injection operation by the second urea water injection device 50B is continued, and the engine 10 is in low load operation. Is the second state in which the injection operation by the second urea water injection device 50B is stopped and the injection operation by the first urea water injection device 50A is continued (timing T1).

Then, after the filter regeneration control unit 103 stops the injection operation in either the first urea water injection device 50A or the second urea water injection device 50B, the amount of PM accumulated in the PM filter 42 becomes the regeneration start reference value. When it reaches, the injection operation in both the first urea water injection device 50A and the second urea water injection device 50B is stopped (timing T2).

Then, when the amount of ammonia storage of the second SCR catalyst 43 drops to a predetermined value (for example, around 0%), the filter regeneration control unit 103 regenerates the PM filter 42 (that is, operates the engine 10 in the exhaust gas temperature raising mode). ) Is started (timing T3).

The “regeneration start reference value” is set to, for example, about 90% to 100% of the depositable amount of the PM filter 42. Further, the "preparation start reference value" is set to a value about 1% to 15% smaller than the regeneration start reference value, for example, based on the depositable amount of the PM filter 42.

Here, during the adjustment period, when the engine 10 is in high load operation, the injection operation by the first urea water injection device 50A is stopped, and the injection operation by the second urea water injection device 50B is continued. In the second state, when the engine 10 is in low load operation, the injection operation by the second urea water injection device 50B is stopped and the injection operation by the first urea water injection device 50A is continued. This is done for the following reasons.

When the engine 10 is in low load operation (for example, running at a low speed), the exhaust gas is at a low temperature, so that the time required for purging the ammonia of the second SCR catalyst 43 tends to be long during the purging period. On the other hand, in this case, since the amount of NOx in the exhaust gas is relatively small, it is possible to sufficiently purify NOx with only the first SCR catalyst 41. In addition, when the engine 10 is in low load operation, it may be keyed off during running, and if the first SCR catalyst 41 is emptied, the NOx purification rate at low temperature start becomes extremely poor.

In such control, ammonia in the first SCR catalyst 41 often remains, but the amount of ammonia storage in the first SCR catalyst 41 does not need to be reduced to near zero, but rather ammonia in the first SCR catalyst 41. It is desirable that remains. This is because the ammonia in the first SCR catalyst 41 is changed to NOx by the oxidation catalyst (here, PM filter 42) in the subsequent stage even if it is desorbed during the regeneration of the PM filter 42, and the ammonia is converted to NOx in the PM filter 42. This is because it also functions to maintain the NOx purification performance of the exhaust gas purification device U during regeneration. Further, at the time of regeneration of the PM filter 42, the exhaust gas temperature on the upstream side of the oxidation catalyst is lower than the exhaust gas temperature on the downstream side of the oxidation catalyst (for example, about 300 ° C.), and the ammonia from the first SCR catalyst 41 This is because the amount of desorption is relatively small.

On the other hand, when the engine 10 is in high-load operation (for example, high-speed running), the exhaust gas has a high temperature, so that a large amount of ammonia cannot be stored in the first SCR catalyst 41. Further, in this case, the time required for purging the ammonia of the second SCR catalyst 43 is also shortened during the purging period. Further, in this case, since the amount of NOx in the exhaust gas is relatively large, it is desirable to exert the NOx purification function by the second SCR catalyst 43, which has a higher NOx purification performance than the first SCR catalyst 41. In addition, when the high load operation continues for a certain period of time, it is unlikely that the key will be turned off, so that there is no problem even if the first SCR catalyst 41 is left empty. However, as described above, when the amount of ammonia storage in the first SCR catalyst 41 is large, the ammonia purge in the second SCR catalyst 43 does not proceed until the amount of ammonia storage in the first SCR catalyst 41 decreases, so that until before the purge period. In addition, it is desirable to lower the second SCR catalyst 43.

The specific operation flow is as follows (see FIG. 3).

In step S1, the filter regeneration control unit 103 determines whether or not the amount of PM deposited in the PM filter 42 is equal to or greater than the preparation start reference value. Then, when the amount of PM deposited in the PM filter 42 is equal to or greater than the preparation start reference value (S1: YES), the process proceeds to step S2. On the other hand, when the amount of PM deposited in the PM filter 42 is less than the preparation start reference value (S1: NO), the flow of FIG. 3 is terminated without executing any particular treatment.

In step S2, the filter regeneration control unit 103 determines whether or not the engine 10 is in low load operation. Then, when the engine 10 is in low load operation (S2: YES), the process proceeds to step S3. If the engine 10 is not in low load operation (S2: NO), the process proceeds to step S4. The filter regeneration control unit 103 determines whether or not the engine 10 is in low load operation based on, for example, the engine speed and torque of the engine 10.

In step S3, the filter regeneration control unit 103 continues the injection operation of the first urea water injection device 50A and stops the injection operation of the second urea water injection device 50B. That is, the filter regeneration control unit 103 instructs the first injection control unit 101 to continue the control as it is, and commands the second injection control unit 102 to stop the injection operation.

In step S4, the filter regeneration control unit 103 stops the injection operation of the first urea water injection device 50A and continues the injection operation of the second urea water injection device 50B. That is, the filter regeneration control unit 103 commands the first injection control unit 101 to stop the injection operation, and causes the second injection control unit 102 to continue the control as it is.

In step S5, the filter regeneration control unit 103 determines whether or not the amount of PM deposited in the PM filter 42 is equal to or greater than the regeneration start reference value. Then, when the amount of PM deposited in the PM filter 42 is equal to or greater than the regeneration start reference value (S5: YES), the filter regeneration control unit 103 proceeds to step S6, and the amount of PM deposited in the PM filter 42 increases. When it is less than the reproduction start reference value (S5: NO), the flowchart of FIG. 3 is terminated without executing any particular process.

Here, when the amount of PM deposited in the PM filter 42 is less than the regeneration start reference value (S5: NO), the configuration in which the flowchart of FIG. 3 ends is the amount of PM deposited in the PM filter 42. Is equal to or greater than the preparation start reference value and less than the regeneration start reference value, and when the operating state of the engine 10 changes, the operating states of the first urea water injection device 50A and the second urea water injection device 50B also change. Is.

In step S6, the filter regeneration control unit 103 stops the injection operation of the first urea water injection device 50A and stops the injection operation of the second urea water injection device 50B.

In step S7, the filter regeneration control unit 103 determines whether or not the amount of ammonia storage of the second SCR catalyst 43 has decreased to a predetermined value (for example, 1% of the storable amount) or less. Then, the filter regeneration control unit 103 waits for the ammonia storage amount of the second SCR catalyst 43 to decrease to a predetermined value or less (S7: NO), and when the ammonia storage amount of the second SCR catalyst 43 decreases to a predetermined value or less ( S7: YES), the process proceeds to step S8.

In step S8, the filter regeneration control unit 103 commands the engine 10 to operate in the exhaust gas temperature rising mode, and executes regeneration of the PM filter 42.

The PM filter 42 is regenerated by the above flow. Although not shown, after the regeneration of the PM filter 42 is completed, the filter regeneration control unit 103 restarts the injection operations of the first urea water injection device 50A and the second urea water injection device 50B.

Next, with reference to FIGS. 5A and 5B, the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 in the preparation period before the regeneration of the PM filter 42 according to the present embodiment is shown.

When the engine 10 is in low load operation, the injection operation by the second urea water injection device 50B is stopped and the injection operation by the first urea water injection device 50A is continued during the adjustment period. At this time, the amount of ammonia storage of the first SCR catalyst 41 is maintained at a high value, while the amount of ammonia storage of the second SCR catalyst 43 gradually decreases. Then, when entering the purge period, the amount of ammonia storage of the second SCR catalyst 43 will be lower than that before the adjustment period (see FIG. 5A).

During the adjustment period, the NOx discharged from the engine 10 is reduced and purified by the first SCR catalyst 41, so that the amount of NOx discharged to the outside air is extremely small.

Then, when the purging period is entered and the injection operation by the first urea water injection device 50A is also stopped, the ammonia in the second SCR catalyst 43 is purged in a short time as the amount of ammonia storage of the first SCR catalyst 41 decreases.

On the other hand, when the engine 10 is in high load operation, the injection operation by the first urea water injection device 50A is stopped and the injection operation by the second urea water injection device 50B is continued during the adjustment period. At this time, the amount of ammonia storage of the second SCR catalyst 43 is maintained at a high value, while the amount of ammonia storage of the first SCR catalyst 41 decreases in a relatively short time (see FIG. 5B).

During the adjustment period, since the engine 10 is in high load operation, the amount of NOx discharged from the engine 10 is relatively large. However, since the NOx reduction performance of the second SCR catalyst 43 is higher than the NOx reduction performance of the first SCR catalyst 41, it is possible to maintain a high NOx purification rate for the exhaust gas purification device U as a whole even during the adjustment period. ..

Then, the purge period is entered, and the injection operation by the second urea water injection device 50B is stopped. At this time, the amount of ammonia storage of the first SCR catalyst 41 is small, and most of the NOx discharged from the engine 10 is consumed by the second SCR catalyst 43. As a result, the ammonia in the second SCR catalyst 43 is purged in a shorter time than the time required for purging the ammonia in both the first SCR catalyst 41 and the second SCR catalyst 43.

[effect]
As described above, in the exhaust purification device U according to the present embodiment, when the amount of PM accumulated in the PM filter 42 reaches the preparation start reference value, when the engine 10 is in high load operation, the first urea is used. As the first state in which the injection operation by the water injection device 50A is stopped and the injection operation by the second urea water injection device 50B is continued, on the other hand, when the engine 10 is in low load operation, the second urea water is used. The second state is set in which the injection operation by the injection device 50B is stopped and the injection operation by the first urea water injection device 50A is continued.

Therefore, according to the exhaust gas purification device U according to the present embodiment, the amount of NOx discharged before the start of regeneration of the PM filter 42 is reduced while suppressing the discharge of ammonia from the SCR catalyst (particularly, the second SCR catalyst 43) to the outside air. Can be kept to a minimum. Further, according to the exhaust gas purification device U according to the present embodiment, the state in which ammonia is adsorbed on the first SCR catalyst 41 can be maintained even during the regeneration of the PM filter 42 (in particular, only the amount of ammonia storage in the second SCR catalyst 43). The amount of NOx discharged during regeneration of the PM filter 42 can also be reduced.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be considered.

For example, in the above embodiment, as an example of the filter regeneration control unit 103, when the amount of PM deposited in the PM filter 42 reaches the regeneration start reference value, the first urea water injection device 50A and the second urea water injection device 50B The mode of stopping the injection operation in both of the above is shown. However, as described above, when the PM filter 42 is being regenerated, the ammonia remaining in the first SCR catalyst 41 does not pose a problem. From this point of view, in the present invention, even after the amount of PM deposited in the PM filter 42 reaches the regeneration start reference value, the injection operation of the first urea water injection device 50A is continued (or restarted). May be good.

Further, in the above embodiment, as an example of the filter regeneration control unit 103, an embodiment in which the time width of the purge period is set based on the amount of ammonia storage of the first SCR catalyst 41 is shown. However, in the present invention, the mode for setting the time width of the purge period can be changed in various ways, and may be, for example, a preset time width.

Further, in the above embodiment, as an example of various sensors, a first NOx sensor 61, a second NOx sensor 62, a first temperature sensor 63, a second temperature sensor 64, and a flow rate sensor 65 are shown. However, the method by which the ECU 100 detects the state of the exhaust gas passing through the exhaust pipe 30, the state of the first SCR catalyst 41, the state of the second SCR catalyst 43, etc. is arbitrary, and the sensor values of other sensors are used. It may be obtained indirectly by arithmetic processing.

Further, in the above embodiment, the vehicle is shown as an example of the application target of the exhaust gas purification device U, but the application target of the exhaust gas purification device U is not limited to this. For example, the exhaust gas purification device U may be applied to a generator, a construction machine, a ship, or the like.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above.

According to the exhaust gas purification device according to the present disclosure, it is possible to reduce the amount of NOx emitted when the PM filter is regenerated.

U exhaust purification device 10 engine 20 intake pipe 30 exhaust pipe 41 1st SCR catalyst 42 PM filter 43 2nd SCR catalyst 50A 1st urea water injection device 50B 2nd urea water injection device 51A, 51B urea water addition valve 52A, 52B urea water tank 53A, 53B Supply pump 61 1st NOx sensor 62 2nd NOx sensor 63 1st temperature sensor 64 2nd temperature sensor 65 Flow sensor 66 Differential pressure sensor 100 ECU (control device)
101 1st injection control unit 102 2nd injection control unit 103 Filter regeneration control unit

Claims (6)

A first SCR catalyst, a PM filter, and a second SCR catalyst arranged in order from the upstream side to the downstream side in the exhaust pipe of the internal combustion engine.
A first urea water injection device that injects urea water on the upstream side of the first SCR catalyst in the exhaust pipe,
A second urea water injection device that injects urea water between the second SCR catalyst and the PM filter in the exhaust pipe, and a second urea water injection device.
A control device that controls each of the first and second urea water injection devices and also controls the regeneration timing of the PM filter.
With
When the amount of PM deposited in the PM filter reaches a preparation start reference value smaller than the regeneration start reference value of the PM filter, the control device is used.
When the internal combustion engine is in high-load operation, the PM filter is in the first state in which the injection operation by the first urea water injection device is stopped and the injection operation by the second urea water injection device is continued. Wait until the PM accumulation amount in the medium reaches the regeneration start reference value.
When the internal combustion engine is in low load operation, the PM filter is in a second state in which the injection operation by the second urea water injection device is stopped and the injection operation by the first urea water injection device is continued. Wait until the PM accumulation amount in the medium reaches the regeneration start reference value.
Exhaust purification device. When the control device controls the first and second urea water injection devices to the first state or the second state, and then the amount of PM deposited in the PM filter reaches the regeneration start reference value. , Stops the injection operation in both the first and second urea water injection devices.
The exhaust purification device according to claim 1. The control device stops the injection operation in both the first and second urea water injection devices, reduces the amount of ammonia storage of the second SCR catalyst to a predetermined value or less, and then puts the internal combustion engine into an exhaust gas temperature raising mode. To drive with
The exhaust purification device according to claim 2. After finishing the regeneration of the PM filter, the control device restarts the injection operation of both the first and second urea water injection devices.
The exhaust gas purification device according to any one of claims 1 to 3. The control device executes the regeneration of the PM filter with the ammonia in the first SCR catalyst remaining.
The exhaust gas purification device according to any one of claims 1 to 4. A vehicle having the exhaust gas purification device according to any one of claims 1 to 5.

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