JP7200896B2 - Exhaust purification device for internal combustion engine and vehicle - Google Patents

Description

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

Conventionally, an internal combustion engine exhaust purification device 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. known (see, for example, Patent Literature 1).

In this type of exhaust purification device, the urea water injected into the exhaust pipe from the urea water injection device is hydrolyzed to generate ammonia, the ammonia and NOx are reacted in the SCR catalyst, and the NOx is converted to nitrogen. and water.

In recent years, in this type of exhaust purification device, due to the demand for further improving exhaust emission, an upstream SCR catalyst, a particulate filter (hereinafter referred to as "PM filter"), Also, a configuration in which the downstream SCR catalysts are arranged in order is being studied.

JP 2018-009581 A

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

Conventionally, in this type of exhaust purification system, before regeneration of the PM filter, the urea water injection by the urea water injection device is stopped (or limited to a small amount of protective injection). Wait for a certain period of time, and after the amount of ammonia storage in the SCR catalyst (meaning the amount of ammonia adsorbed on the SCR catalyst; the same shall apply hereinafter) decreases, regeneration of the PM filter (that is, the engine is operated in the exhaust gas temperature raising mode) is started. control is in place. The reason for performing such control is to prevent ammonia in the SCR catalyst from detaching and flowing out due to an increase in the temperature of the exhaust gas during regeneration of the PM filter.

However, in an exhaust purification device provided with two SCR catalysts, as in the conventional case, before regeneration of the PM filter is started, an upstream side urea water injection device that supplies urea water to the upstream side SCR catalyst and a downstream side SCR catalyst. If a waiting time is provided in which the injection operations of both downstream urea water injection devices that supply urea water to the catalyst are stopped, the waiting time becomes longer. The reason for this is that most of the NOx emitted 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 one by one (described later with reference to FIG. 6).

Since the SCR catalyst cannot exhibit sufficient NOx purification performance in a state where the ammonia storage amount is low, during the standby time until the ammonia storage amount of the downstream SCR catalyst is low, exhaust gas purification The NOx purification rate of the system as a whole is also lowered. 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 an object thereof is to provide an exhaust purification device for an internal combustion engine and a vehicle capable of reducing the amount of NOx emitted when the PM filter is regenerated.

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 upstream to downstream in an exhaust pipe of an internal combustion engine;
a first urea water injection device for injecting urea water upstream of the first SCR catalyst in the exhaust pipe;
a second urea water injection device for injecting urea water between the second SCR catalyst and the PM filter in the exhaust pipe;
a control device that controls each of the first and second aqueous urea injection devices and controls regeneration timing of the PM filter;
with
When the PM deposition amount in the PM filter reaches a preparation start reference value smaller than the regeneration start reference value of the PM filter, the control device
When the internal combustion engine is operating under high load, the PM filter is in a 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. Standby until the amount of PM accumulated in the medium reaches the regeneration start reference value,
When the internal combustion engine is operating at a low load, 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 amount of PM accumulated in the medium reaches the regeneration start reference value;
It is an exhaust purification device.

Also, in other aspects,
A vehicle including the above exhaust purification device.

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

A diagram showing an example of the configuration of an exhaust purification device according to one embodiment. A diagram showing an example of a configuration of a first injection control unit according to one embodiment. The figure which shows an example of a structure of the 2nd injection control part which concerns on one Embodiment. 4 is a flow chart showing an example of the operation of a filter regeneration control unit according to one embodiment; A diagram showing an example of the relationship between the PM deposition amount in the PM filter and the preparation period for purging the ammonia in the second SCR catalyst in the exhaust purification device according to one embodiment. FIG. 4 is a diagram showing an example of the behavior of ammonia storage amounts of the first SCR catalyst and the second SCR catalyst during a preparation period before starting regeneration in the PM filter in the exhaust purification device according to one embodiment; FIG. 4 is a diagram showing an example of the behavior of ammonia storage amounts of the first SCR catalyst and the second SCR catalyst during a preparation period before starting regeneration in the PM filter in the exhaust purification device according to one embodiment; A diagram showing an example of the behavior of the ammonia storage amount of the first SCR catalyst and the second SCR catalyst in the conventional technology A diagram showing an example of the behavior of the device

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functions are denoted by the same reference numerals, thereby omitting redundant description.

[Configuration of exhaust gas purification device]
Hereinafter, with reference to FIG. 1, the configuration of an exhaust purification system according to one embodiment will be described.

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

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

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

The engine 10 includes, for example, a combustion chamber, a fuel injection device for injecting fuel in the combustion chamber, and the like (not shown). Engine 10 combusts and expands a mixture of fuel and air in a combustion chamber to generate power. The engine 10 is connected to an intake pipe 20 that introduces air into the combustion chamber and an exhaust pipe 30 that discharges post-combustion exhaust gas from the combustion chamber to the outside of the vehicle.

The exhaust 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, from the upstream side to the downstream side, there are a urea water addition valve 51A of the first urea water injection device 50A, a first SCR catalyst 41, a PM filter 42, and a urea water addition valve of the second urea water injection device 50B. 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 made of, for example, cordierite or silicon carbide porous ceramics, and has a honeycomb structure in which inlets and outlets are alternately plugged so that the exhaust gas passes through collection walls made of the porous ceramics. presenting. Exhaust gas discharged from the engine 10 flows downstream while passing through the porous collection wall of the PM filter 42, during which PM is collected by the collection wall.

The PM filter 42 carries an oxidation catalyst that oxidizes 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. Incidentally, such an oxidation catalyst may be arranged on the upstream side of the PM filter 42 so as to be carried by a carrier separate from the PM filter 42 .

The first SCR catalyst 41 adsorbs ammonia hydrolyzed by the urea water injected from the first urea water injection device 50A, and selectively reduces and purifies NOx in the exhaust gas with the adsorbed ammonia. The first SCR catalyst 41 is arranged upstream of the PM filter 42 , for example, directly below the engine 10 . As a result, the first SCR catalyst 41 becomes susceptible to the temperature of the exhaust gas emitted by the engine 10, and can be activated early even immediately after the engine 10 is started.

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

A known SCR catalyst can be used as the first SCR catalyst 41 and the second SCR catalyst 43. For example, a NOx reduction catalyst such as Fe zeolite, Cu zeolite, or vanadium is supported on the surface of a ceramic support. can be used. The first SCR catalyst 41 and the second SCR catalyst 43 may be of a type that converts urea water into ammonia on the catalyst.

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

In the first urea water injection device 50A, the urea water pressure-fed by the supply pump 53A from the urea water tank 52A is injected into the exhaust pipe 30 through the urea water addition valve 51A. The urea water injected from the urea water addition valve 51</b>A into the exhaust pipe 30 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 into the exhaust pipe 30 is adjusted by adjusting the opening of the urea water addition valve 51A. The opening degree of the urea solution addition valve 51A is controlled by a control signal output from the ECU 100 (first injection control section 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 into the exhaust pipe 30 is adjusted by adjusting the opening of the urea water addition valve 51B. The opening degree of the urea solution addition valve 51B is controlled by a control signal output from the ECU 100 (second injection control section 102).

Various sensors 61 to 66 are provided to detect the state of exhaust gas flowing 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 equipped 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 equipped with a flow rate sensor 65. there is

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

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

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

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

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

The ECU 100 (corresponding to the "control device" of the present invention) controls the operation of the exhaust 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 of the ECU 100, which will be described later, is realized, for example, by the CPU referring to control programs and various data stored in ROM, RAM, or the like. However, the function is not limited to processing by software, and can of course be realized by a dedicated hardware circuit.

The ECU 100 communicates with the engine 10, the first aqueous urea injection device 50A, the second aqueous urea injection device 50B, and the like to control them and obtain state information thereof. Further, the ECU 100 acquires sensor information from various sensors 61 to 66, and determines the state of the exhaust gas flowing 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. to detect

[Configuration of ECU]
The ECU 100 includes a first injection control section 101 , a second injection control section 102 and a filter regeneration control section 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 the urea water injection amount of the urea water injection device 50 so that, for example, the ammonia storage amount of the first SCR catalyst 41 becomes a predetermined amount. As a result, the first SCR catalyst 41 is maintained at a high NOx purification rate.

FIG. 2A is a diagram showing an example of the configuration of the first injection control section 101. As shown in FIG.

The first injection control unit 101 has, 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 101 a sets a target value for 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 approximately 100% of the storable amount in the first SCR catalyst 41, for example. 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 sets the first SCR indicated by the first temperature sensor 63. A target value for the ammonia storage amount in the first SCR catalyst 41 is set based on the catalyst temperature of the catalyst 41 .

In general, the storage capacity of the SCR catalyst increases as the catalyst temperature decreases. In particular, when the catalyst temperature exceeds a certain temperature, slip (detachment) from the SCR catalyst reduces the storage capacity of the SCR catalyst. Incidentally, the NOx purification rate of the SCR catalyst generally increases as the ammonia storage amount 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 the adsorption amount of ammonia newly adsorbed on the first SCR catalyst 41, for example, 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 amount of ammonia consumed in the first SCR catalyst 41 from the amount of ammonia newly adsorbed in the first SCR catalyst 41, thereby obtaining the current amount of ammonia in the first SCR catalyst 41. to estimate the amount of ammonia storage in That is, the actual ammonia storage amount calculation unit 101b stores in the storage unit (eg, 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 ammonia storage amount to be used 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 rate sensor 65 (that is, the total value of the intake air amount and the fuel injection amount). calculated based on the amount of NOx arriving at the first SCR catalyst 41.

For example, the injection amount determination unit 101c calculates the difference between the current actual value and the target value of the ammonia storage amount in the first SCR catalyst 41, 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 that associates the difference between the current actual value and the target value of the ammonia storage amount in the first SCR catalyst 41 with the urea water injection amount to perform the first urea water injection. Determine the urea water injection amount of the device 50A. 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 determined by itself is obtained.

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

However, the first injection control section 101 is configured to be able to stop the injection operation of the first urea water injection device 50A based on a command from the filter regeneration control section 103 . Here, the state in which the injection operation of the first aqueous urea solution injection device 50A is stopped includes the state in which only a small amount of protective injection is performed (the same shall apply hereinafter).

<Regarding 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, for example, the ammonia storage amount adsorbed to the second SCR catalyst 43 becomes a predetermined amount. As a result, the second SCR catalyst 43 is maintained at a high NOx purification rate.

FIG. 2B is a diagram showing an example of the configuration of the second injection control section 102. As shown in FIG.

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. Note that 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 each set the target ammonia storage amount 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 102 a sets a target value for 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 approximately 100% of the storageable amount in the second SCR catalyst 43, for example. 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 sets the catalyst temperature of the second SCR catalyst 43 indicated by the second temperature sensor 64. , the target value of the ammonia storage amount 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 the adsorption amount of ammonia newly adsorbed on the second SCR catalyst 43, for example, 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 amount of ammonia consumed in the second SCR catalyst 43 from the adsorption amount of ammonia newly adsorbed in the second SCR catalyst 43, so that the current second SCR catalyst 43 to 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 ammonia storage amount to be used 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 rate sensor 65 (that is, the total value of the intake air amount and the fuel injection amount). is calculated based on the amount of NOx arriving at the second SCR catalyst 43.

For example, the injection amount determination unit 102c calculates the difference between the current actual value and the target value of the ammonia storage amount in the second SCR catalyst 43, and based on the difference, determines the urea water injection amount of the second urea water injection device 50B. decide. Note that the injection amount determination unit 102c uses, for example, a control map that associates the difference between the current actual value and the target value of the ammonia storage amount in the second SCR catalyst 43 with the urea water injection amount to perform the second urea water injection. The urea water injection amount of the device 50B is determined. Then, the injection amount determination unit 102c outputs an opening degree command signal to the urea water addition valve 51B of the second urea water injection device 50B so that the urea water injection amount determined by itself is obtained.

In addition, the configuration for controlling the injection amount of urea water from the second urea water injection device 50B by the second injection control unit 102 is not limited to the above-described configuration. The second injection control unit 102, for example, estimates the NOx amount corresponding to the NOx amount arriving at the second SCR catalyst 43 based on the operating state of the engine 10, and adjusts the urea water injection amount of the second urea water injection device 50B. It may be controlled.

However, the second injection control section 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 section 103 . Here, the state in which the injection operation of the second aqueous urea solution injection device 50B is stopped includes the state in which only a small amount of protective injection is performed (the same shall apply hereinafter).

<Regarding Filter Regeneration Control Unit 103>
The filter regeneration control unit 103 monitors the amount of PM deposited on the PM filter 42, performs preparations before regeneration of the PM filter 42, and executes regeneration of the PM filter 42 based on the PM deposition amount. .

The filter regeneration control unit 103 calculates, for example, the pressure loss caused by the PM deposited in the PM filter 42 from the differential pressure across the PM filter 42 indicated by the differential pressure sensor 66, thereby determining the PM deposition amount in the PM filter 42. to estimate Then, the filter regeneration control unit 103 regenerates the PM filter 42 when the PM deposition amount in the PM filter 42 becomes equal to or greater than the regeneration start reference value.

When regenerating the PM filter 42, the filter regeneration control unit 103, for example, outputs a control signal to the engine 10 to operate the engine 10 in the exhaust gas temperature raising mode. In the exhaust gas temperature raising mode, the engine 10 raises the temperature of the exhaust gas to about 500° C., for example, by increasing the amount of fuel injected from the injectors or performing multi-injection. In addition, as a method for causing 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 executing regeneration of the PM filter 42, the filter regeneration control unit 103 prevents ammonia in the second SCR catalyst 43 from being detached and discharged to the outside air due to an increase in exhaust gas temperature. The first aqueous urea injection device 50A and the second urea water injection device 50A and the second It controls the injection operation of the urea water injection device 50B.

FIG. 3 is a flow chart showing an example of the operation of the filter regeneration control section 103 according to this embodiment. Note that the flowchart of FIG. 3 is a process repeatedly executed at predetermined intervals (for example, 100 ms intervals) by the filter regeneration control unit 103 according to a computer program.

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

5A and 5B are diagrams showing an example of the behavior of the amount of ammonia stored in the first SCR catalyst 41 and the second SCR catalyst 43 during the preparatory period before starting regeneration in the PM filter 42. FIG. FIG. 5A shows the behavior of the ammonia storage amount of the first SCR catalyst 41 and the second SCR catalyst 43 when the PM deposition amount in the PM filter 42 reaches the preparation start reference value and the engine 10 is operating at low load. show. FIG. 5B shows the behavior of the ammonia storage amounts of the first SCR catalyst 41 and the second SCR catalyst 43 when the PM deposition amount in the PM filter 42 reaches the preparation start reference value and the engine 10 is operating under high load. show.

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

4, 5A, 5B, and 6, T1 is the timing at which the injection operation of either the first urea water injection device 50A or the second urea water injection device 50B is stopped (the filter regeneration control unit 103 adjusts ), T2 represents the timing to stop the injection operations in both the first aqueous urea injection device 50A and the second aqueous urea injection device 50B, and T3 represents the timing to start regeneration of the PM filter 42.

In the prior art, the first urea water injection device 50A and the second urea water injection device 50A and the second Both of the two urea water injection devices 50B are operated normally. Then, when the PM deposition amount in the PM filter 42 reaches the regeneration start reference value, both the first urea water injection device 50A and the second urea water injection device 50B stop operating, and the second SCR catalyst 43 until the ammonia storage amount of the second SCR catalyst 43 reaches around 0%, and after the ammonia storage amount of the second SCR catalyst 43 reaches around 0%, regeneration of the PM filter 42 is started (i.e., the engine 10 is operated in the exhaust gas temperature raising mode cause).

However, depending on such conventional control, as shown in FIG. 6, after the operations of both the first urea water injection device 50A and the second urea water injection device 50B are stopped, the ammonia storage amount of the second SCR catalyst 43 It takes a long time to decrease to near zero%. This is because, as described above, depending on the conventional control, NOx in the exhaust gas discharged from the engine 10 after stopping the operation of the first aqueous urea injection device 50A and the second aqueous urea injection device 50B This is because the ammonia storage amount in the second SCR catalyst 43 decreases at an extremely slow rate because it is consumed in the first SCR catalyst 41 . Therefore, depending on the conventional control, a large amount of NOx is discharged to the outside air not only at the start of regeneration of the PM filter 42 but also before the regeneration of the PM filter 42 is started. In addition, the delayed start of regeneration of the PM filter 42 causes excessive collection of PM in the PM filter 42, increasing the risk of filter damage.

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

Specifically, when the amount of PM deposited in the PM filter 42 reaches a preparation start reference value that is somewhat smaller than the regeneration start reference value of the PM filter 42, the filter regeneration control unit 103 determines that the engine 10 is operating under high load. In the case of , the injection operation by the first aqueous urea solution injection device 50A is stopped and the injection operation by the second urea solution injection device 50B is continued in the first state, and when the engine 10 is operating at a low load, is a 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, the filter regeneration control unit 103 stops the injection operation in either the first aqueous urea injection device 50A or the second aqueous urea injection device 50B, and then the amount of accumulated PM in the PM filter 42 reaches the regeneration start reference value. When it reaches, the injection operations of both the first aqueous urea solution injection device 50A and the second aqueous urea solution injection device 50B are stopped (timing T2).

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

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

Here, in the adjustment period, when the engine 10 is in high load operation, the injection operation by the first aqueous urea solution injection device 50A is stopped and the injection operation by the second aqueous urea solution injection device 50B is continued. A second state in which the injection operation by the second aqueous urea solution injection device 50B is stopped and the injection operation by the first aqueous urea solution injection device 50A is continued when the engine 10 is operating under a low load. The reason for this is as follows.

When the engine 10 is running at a low load (for example, running at low speed), the exhaust gas is at a low temperature, so the time required to purge ammonia from the second SCR catalyst 43 tends to be longer during the purge period. On the other hand, in this case, since the amount of NOx in the exhaust gas is relatively small, the first SCR catalyst 41 alone can sufficiently purify NOx. In addition, when the engine 10 is operating at a low load, there is a possibility that the vehicle will be keyed off while the vehicle is running. If the first SCR catalyst 41 is empty, the NOx purification rate at low temperature start will be extremely poor.

Under such control, ammonia often remains in the first SCR catalyst 41, but it is not necessary to reduce the ammonia storage amount of the first SCR catalyst 41 to near zero. should remain. This is because even if the ammonia in the first SCR catalyst 41 is desorbed during regeneration of the PM filter 42, it is changed to NOx by the subsequent oxidation catalyst (here, the PM filter 42), and the ammonia is removed from the PM filter 42. This is because it also functions to maintain the NOx purification performance of the exhaust purification device U during regeneration. Further, when the PM filter 42 is regenerated, the temperature of the exhaust gas on the upstream side of the oxidation catalyst is lower than the temperature of the exhaust gas on the downstream side of the oxidation catalyst (for example, about 300° C.). This is because the desorption amount is relatively small.

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

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

In step S1, the filter regeneration control unit 103 determines whether or not the PM deposition amount in the PM filter 42 is equal to or greater than the preparation start reference value. Then, if the PM deposition amount 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 PM deposition amount 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 process.

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

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, and instructs 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 aqueous urea injection device 50A and continues the injection operation of the second aqueous urea injection device 50B. That is, the filter regeneration control unit 103 instructs the first injection control unit 101 to stop the injection operation, and causes the second injection control unit 102 to continue the control.

In step S5, the filter regeneration control unit 103 determines whether or not the PM deposition amount in the PM filter 42 is equal to or greater than the regeneration start reference value. Then, when the PM deposition amount in the PM filter 42 is equal to or greater than the regeneration start reference value (S5: YES), the filter regeneration control unit 103 advances the process to step S6, and the PM deposition amount in the PM filter 42 reaches If it is less than the regeneration 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 flow chart of FIG. is greater than or equal to the preparation start reference value and less than the regeneration start reference value, the operation states of the first urea water injection device 50A and the second urea water injection device 50B are also changed when the operating state of the engine 10 changes. 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 ammonia storage amount of the second SCR catalyst 43 has decreased to a predetermined value (for example, 1% of the available storage 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 S<b>8 , the filter regeneration control unit 103 instructs the engine 10 to operate in the exhaust gas temperature increasing mode, and regenerates the PM filter 42 .

The regeneration of the PM filter 42 is performed according to the above flow. Although not shown, after 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 during the preparatory period before regeneration of the PM filter 42 according to this embodiment is shown.

When the engine 10 is in low-load operation, the injection operation by the second aqueous urea injection device 50B is stopped and the injection operation by the first aqueous urea injection device 50A is continued during the adjustment period. At this time, the ammonia storage amount of the first SCR catalyst 41 is maintained at a high value, while the ammonia storage amount of the second SCR catalyst 43 gradually decreases. Then, when entering the purge period, the ammonia storage amount of the second SCR catalyst 43 is lower than 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 the amount of NOx discharged to the outside air is extremely small.

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

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

During the adjustment period, the engine 10 is operating under high load, so the amount of NOx emitted 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, the exhaust purification device U as a whole can maintain a high NOx purification rate even during the adjustment period. .

Then, the purge period starts, and the injection operation by the second urea water injection device 50B is stopped. At this time, the ammonia storage amount of the first SCR catalyst 41 is small, and most of the NOx emitted 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 short time compared to the time required to purge 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 PM deposition amount in the PM filter 42 reaches the preparation start reference value, the first urea As a 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 operating at a low load, the second urea water A second state is established in which the injection operation by the injection device 50B is stopped and the injection operation by the first aqueous urea solution injection device 50A is continued.

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

(Other embodiments)
The present invention is not limited to the above-described embodiment, and various modifications are conceivable.

For example, in the above embodiment, as an example of the filter regeneration control unit 103, when the PM deposition amount in the PM filter 42 reaches the regeneration start reference value, the first aqueous urea injection device 50A and the second aqueous urea injection device 50B has been shown to stop the injection operation in both. However, as described above, ammonia remaining in the first SCR catalyst 41 poses no problem when the PM filter 42 is being regenerated. 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 first urea water injection device 50A continues (or restarts) the injection operation. good too.

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

Moreover, in the above embodiment, the first NOx sensor 61, the second NOx sensor 62, the first temperature sensor 63, the second temperature sensor 64, and the flow rate sensor 65 are shown as examples of various sensors. However, the method by which the ECU 100 detects the state of the exhaust gas flowing 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 sensor values of other sensors are used. may be obtained indirectly by arithmetic processing.

Further, in the above embodiment, a vehicle is shown as an example of an application target of the exhaust purification device U, but the application target of the exhaust purification device U is not limited to this. For example, the exhaust purification device U may be applied to generators, construction machinery, ships, and 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 the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

According to the exhaust 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 First SCR catalyst 42 PM filter 43 Second SCR catalyst 50A First aqueous urea injection device 50B Second aqueous urea injection device 51A, 51B Aqueous urea addition valve 52A, 52B Aqueous urea tank 53A, 53B supply pump 61 first NOx sensor 62 second NOx sensor 63 first temperature sensor 64 second temperature sensor 65 flow rate sensor 66 differential pressure sensor 100 ECU (control device)
101 first injection control section 102 second injection control section 103 filter regeneration control section

Claims (6)

a first SCR catalyst, a PM filter, and a second SCR catalyst arranged in order from upstream to downstream in an exhaust pipe of an internal combustion engine;
a first urea water injection device for injecting urea water upstream of the first SCR catalyst in the exhaust pipe;
a second urea water injection device for injecting urea water between the second SCR catalyst and the PM filter in the exhaust pipe;
a control device that controls each of the first and second aqueous urea injection devices and controls regeneration timing of the PM filter;
with
When the PM deposition amount in the PM filter reaches a preparation start reference value smaller than the regeneration start reference value of the PM filter, the control device
When the internal combustion engine is operating under high load, the PM filter is in a 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. Standby until the amount of PM accumulated in the medium reaches the regeneration start reference value,
When the internal combustion engine is operating at a low load, 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 amount of PM accumulated in the medium reaches the regeneration start reference value;
Exhaust purification device. After the control device controls the first and second urea water injection devices to the first state or the second state, when the PM deposition amount in the PM filter reaches the regeneration start reference value , stopping the injection operation in both the first and second aqueous urea injection devices;
The exhaust purification device according to claim 1. The control device stops the injection operations of both the first and second urea water injection devices, and after the ammonia storage amount of the second SCR catalyst has decreased to a predetermined value or less, the internal combustion engine is put into an exhaust gas temperature increasing mode. to drive with
The exhaust purification device according to claim 2. The control device restarts the injection operations of both the first and second aqueous urea injection devices after completing the regeneration of the PM filter.
The exhaust purification device according to any one of claims 1 to 3. The control device regenerates the PM filter while ammonia remains in the first SCR catalyst.
The exhaust purification device according to any one of claims 1 to 4. A vehicle comprising the exhaust purification device according to any one of claims 1 to 5.

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