WO2016084564A1

WO2016084564A1 - Engine exhaust purification control method

Info

Publication number: WO2016084564A1
Application number: PCT/JP2015/081085
Authority: WO
Inventors: 孝則村崎
Original assignee: 株式会社豊田自動織機
Priority date: 2014-11-27
Filing date: 2015-11-04
Publication date: 2016-06-02
Also published as: JP2016102433A

Abstract

An engine exhaust purification control method, provided with a step for determining whether or not warm-up of an oxidation catalyst is necessary, and a step for determining whether or not operation of a chemical heat storage device is possible. If it is determined that warm-up of the oxidation catalyst is necessary and it is determined that operation of the chemical heat storage device is possible, the chemical heat storage device is operated so as to warm up the oxidation catalyst. Alternatively, if it is determined that warm-up of the oxidation catalyst is necessary and it is determined that operation of the chemical heat storage device is not possible, control of the engine is switched to exhaust priority control and discharge of atmospheric pollutants in the exhaust gas to the outside air is reduced.

Description

Engine exhaust purification control method

The present invention relates to an engine exhaust purification control method by an exhaust purification system including an exhaust gas purification catalyst provided on an exhaust passage and a chemical heat storage device capable of warming up the catalyst.

The vehicle exhaust system is provided with various catalysts for purifying environmental pollutants such as HC, CO, NOx contained in the exhaust gas discharged from the engine. These catalysts have an activation temperature, which is a temperature at which they are activated and have a high purification capacity. However, when the engine is cold and the engine is not warm, the temperature of the exhaust gas exhausted from the engine is low. Therefore, it takes a long time to heat the catalyst to the activation temperature only with the heat of the exhaust gas. For this reason, there is a possibility that environmental pollutants contained in the exhaust gas are not sufficiently purified at the initial stage when the engine is cold started.

Therefore, an apparatus for activating the catalyst in a short time is required when the temperature of the exhaust gas is low, such as when the engine is cold started. As this type of device, there is known a chemical heat storage device capable of warming up a catalyst as a heating target in a short time while suppressing deterioration in fuel consumption. The chemical heat storage device uses heat generated by a chemical reaction between the heat storage material and the reaction medium. Patent Document 1 discloses a chemical heat storage type catalyst that warms up a catalyst using heat generated by a chemical reaction between a heat storage material disposed on the outer periphery of a catalyst ceramic portion that supports a catalyst for purifying exhaust gas and a reaction medium. A warm-up device is disclosed.

In an exhaust purification system having such an exhaust gas purification catalyst and a chemical heat storage device for warming up the catalyst, even if the chemical heat storage device cannot be operated, a certain exhaust purification performance is exhibited. It is hoped that.

JP 59-208118 A

An object of the present invention is to provide an engine exhaust gas purification control method capable of exhibiting a certain exhaust gas purification performance by engine control even when a chemical heat storage device cannot be operated.

In order to solve the above problems, according to a first aspect of the present invention, an exhaust gas purifying catalyst provided on an exhaust passage through which exhaust gas discharged from an engine flows, and a chemical capable of warming up the catalyst are provided. An exhaust purification control method for an engine by an exhaust purification system including a heat storage device is provided. The control method includes a step of determining whether or not the catalyst needs to be warmed up and a step of determining whether or not the chemical heat storage device can be operated. According to the control method, when it is determined that the catalyst needs to be warmed up and it is determined that the chemical heat storage device is operable, the chemical heat storage device is operated so as to warm up the catalyst. Also, if it is determined that the catalyst needs to be warmed up and the chemical heat storage device is not operational, the engine control is switched to exhaust priority control to reduce the emission of air pollutants in the exhaust gas to the outside air To do.

According to this configuration, for example, the catalyst can be warmed up by the chemical heat storage device as compared with the case where the catalyst is warmed up only by the heat from the exhaust gas. The exhaust gas can be purified. On the other hand, if the chemical heat storage device is not ready for operation, that is, if it is determined that the chemical heat storage device cannot be operated, the engine is switched to exhaust priority control to warm up the catalyst and purify the exhaust gas. be able to. For this reason, even if the chemical heat storage device cannot be operated, a certain exhaust purification performance can be exhibited by engine control.

The schematic block diagram which shows an exhaust gas purification system. Sectional drawing of a reactor. The flowchart which shows the control procedure after engine starting. The flowchart which shows the control procedure at the time of driving | running | working. The flowchart which shows another example of the control procedure after engine starting.

Hereinafter, an embodiment embodying an engine exhaust gas purification control method in a vehicle will be described with reference to FIGS. First, an exhaust purification system mounted on a vehicle will be described.
As shown in FIG. 1, an exhaust passage 12 is connected to the exhaust side of the engine 11. The exhaust passage 12 is provided with various exhaust gas purification catalysts. Hereinafter, the oxidation catalyst 13 shown in FIG. 1 will be described as an example. The engine 11 is a diesel engine. The oxidation catalyst 13 is a catalyst for purifying exhaust gas, and oxidizes air pollutants such as HC, CO, PM, NOx contained in the exhaust gas discharged from the engine 11. The oxidation catalyst 13 is carried on a catalyst carrying portion 12 a such as a ceramic honeycomb provided in the middle of the exhaust passage 12. The exhaust gas that has passed through the oxidation catalyst 13 passes through various catalysts and filters such as an SCR catalyst and a DPF (not shown) on the exhaust passage 12 and is discharged out of the vehicle.

The oxidation catalyst 13 and each exhaust gas purification catalyst provided downstream of the oxidation catalyst 13 have an activation temperature that is a temperature at which they are activated and exhibit sufficient purification ability, that is, an optimum temperature region. For example, the lower limit of the activation temperature of the oxidation catalyst 13 is about 150 ° C. However, when the engine 11 is cold started, the engine 11 is not sufficiently warmed. For this reason, the temperature of the exhaust gas immediately after being discharged from the engine 11 is relatively low, about 100 ° C. Therefore, in order to make the oxidation catalyst 13 exhibit high purification ability even when the engine 11 is cold started, it is necessary to quickly raise the temperature of the oxidation catalyst 13 to the activation temperature or higher, that is, to warm up the catalyst. Therefore, the exhaust purification system 10 has a chemical heat storage device 20 for warming up the oxidation catalyst 13.

The chemical heat storage device 20 uses a reversible chemical reaction to heat an object to be heated without external energy. Specifically, the chemical heat storage device 20 stores the heat of the exhaust gas in the chemical heat storage device 20 in a state of being separated into a heat storage material and a reaction medium. The chemical heat storage device 20 supplies the reaction medium to the heat storage material when necessary. And the chemical heat storage apparatus 20 heats a heating target object by making the thermal storage material and the reaction medium chemically react (chemical adsorption), and utilizing the reaction heat at the time of a chemical reaction. In this embodiment, the reaction medium is ammonia.

The chemical heat storage device 20 includes a heat storage material 23 and a reactor 21. The reactor 21 is arranged at a position corresponding to the heating object in order to exchange heat with the heating object. In this embodiment, a high heat conduction honeycomb 22 is provided as an object to be heated inside an installation portion 12 b that is a part of the exhaust passage 12. That is, the reactor 21 is provided around the installation portion 12 b that constitutes the exhaust passage 12 in order to exchange heat with the high thermal conductivity honeycomb 22. The high thermal conductive honeycomb 22 is thermally coupled to the installation portion 12b. That is, in the exhaust gas discharge direction X, the high thermal conductivity honeycomb 22 is provided upstream of the oxidation catalyst 13, and the reactor 21 is also provided upstream of the oxidation catalyst 13. Therefore, when the chemical heat storage device 20 is operated, the exhaust gas is heated by the reactor 21 before passing through the oxidation catalyst 13.

In this embodiment, the high thermal conductivity honeycomb 22 disposed upstream of the oxidation catalyst 13 is heated by the reactor 21. As a result, the exhaust gas passing through the high thermal conductive honeycomb 22 is warmed. Then, the exhaust gas purification oxidation catalyst 13 is indirectly warmed up by the warmed exhaust gas. However, the present invention is not limited to this. The oxidation catalyst 13 for purifying exhaust gas is an object to be heated, the reactor 21 is disposed around the oxidation catalyst 13, and the oxidation catalyst 13 for purifying exhaust gas is directly warmed up. May be.

As shown in FIG. 2, a plurality of heat storage materials 23 that chemically react with ammonia as a reaction medium are provided inside the reactor 21. The reactor 21 generates heat by chemically reacting ammonia and the heat storage material 23. As the heat storage material, a metal chloride, a metal bromide, a metal iodide compound, or the like is used. For example, MgCl ₂ , CaCl ₂ , NiCl ₂ , ZnCl ₂ , SrCl ₂ are used. When CaO is used as the heat storage material, water may be used as the reaction medium. If a chemical reaction with the heat storage material is possible, the combination of the heat storage material and the reaction medium may be changed as appropriate.

The heat storage material 23 is arrange | positioned at the outer peripheral surface of the installation part 12b. The plurality of heat storage materials 23 are in contact with the outer peripheral surface of the installation portion 12b. Therefore, the heat generated from each heat storage material 23 is transmitted to the high thermal conductive honeycomb 22 through the installation portion 12b. The reactor 21 has a heat insulating material 25 arranged on the outer peripheral side of the plurality of heat storage materials 23. As the heat insulating material 25, a hard heat insulating material may be used in order to suppress the heat storage material 23 from expanding in the radial direction.

The reactor 21 has a cylindrical casing 26 that covers the installation portion 12b of the exhaust passage 12 from the outer peripheral side. The casing 26 has flange portions 26a at both axial ends thereof. The flange part 26a protrudes from the cylindrical part of the casing 26 toward the installation part 12b. The inner peripheral surface of the flange portion 26a is joined to the outer peripheral surface of the installation portion 12b.

The flange portion 26a covers both ends of the heat storage material 23 and the heat insulating material 25 in the axial direction. The cylindrical portion of the casing 26 covers the outer peripheral surface of the heat insulating material 25. Therefore, the space defined by the casing 26 and the installation part 12b is sealed. The heat storage material 23 and the heat insulating material 25 are enclosed in the sealed space.

As shown in FIG. 1, the chemical heat storage device 20 includes a reservoir 30 that stores a reaction medium that chemically reacts with the heat storage material 23. The reservoir 30 contains activated carbon as an adsorbent that physically adsorbs ammonia as a reaction medium. In the reservoir 30, the ammonia is physically adsorbed on the activated carbon to store the ammonia, and the ammonia is separated from the activated carbon to release the ammonia.

The chemical heat storage device 20 includes a connecting pipe 40 for connecting the reactor 21 and the storage 30 so that ammonia can be circulated. Furthermore, the chemical heat storage device 20 includes an on-off valve 41 provided in the connection pipe 40. The connection pipe 40 is a pipe line for moving ammonia between the reactor 21 and the reservoir 30. When the on-off valve 41 is opened, ammonia moves between the reactor 21 and the reservoir 30 via the connection pipe 40. The on-off valve 41 is connected to the ECU 50 by a signal.

The exhaust purification system 10 includes an upstream temperature sensor 27 in the exhaust passage 12. The upstream temperature sensor 27 is installed upstream of the chemical heat storage device 20 in the exhaust gas discharge direction X. The upstream temperature sensor 27 detects the temperature of the exhaust gas before passing through the high thermal conductive honeycomb 22. That is, the upstream temperature sensor 27 detects the temperature of the exhaust gas immediately after being discharged from the engine 11. Further, the exhaust purification system 10 includes a downstream temperature sensor 28 in the exhaust passage 12. The downstream temperature sensor 28 is installed downstream of the chemical heat storage device 20 and upstream of the oxidation catalyst 13 in the exhaust gas discharge direction X. The downstream temperature sensor 28 detects the temperature of the exhaust gas that has passed through the high thermal conductivity honeycomb 22 and has not passed through the oxidation catalyst 13. Therefore, the upstream temperature sensor 27 and the downstream temperature sensor 28 detect the temperature of the exhaust gas upstream of the oxidation catalyst 13. The upstream temperature sensor 27 and the downstream temperature sensor 28 are connected to the ECU 50 by signals.

Further, the exhaust purification system 10 includes a pressure sensor 31 that detects the pressure of the reservoir 30. The exhaust purification system also includes a temperature sensor 32 that detects the temperature of the reservoir 30. The pressure sensor 31 and the temperature sensor 32 are connected to the ECU 50 by signals.

Next, the operation of the chemical heat storage device 20 in the exhaust purification system 10 will be described. It is assumed that the on-off valve 41 is closed by the ECU 50 while the engine 11 is stopped. Therefore, ammonia is not supplied to the reactor 21 through the connection pipe 40 while the vehicle is stopped.

After the engine 11 is started, the temperature of the exhaust gas immediately after being discharged from the engine 11 is detected by the upstream temperature sensor 27. When the temperature of the exhaust gas immediately after being discharged from the engine 11 is lower than the activation temperature of the oxidation catalyst 13, the temperature of the exhaust gas is raised. Then, the oxidation catalyst 13 is warmed up by the exhaust gas after the temperature rise.

First, the on-off valve 41 is opened by the ECU 50. In the initial state, the pressure of the reservoir 30 for storing ammonia is higher than the pressure of the reactor 21. For this reason, ammonia moves from the reservoir 30 to the reactor 21 by opening the on-off valve 41. That is, ammonia moves due to the pressure difference between the two containers.

Ammonia is supplied to the heat storage material 23 inside the reactor 21. Each heat storage material 23 chemically reacts with the supplied ammonia (coordination bond), adsorbs ammonia, and generates heat. The heat generated from each heat storage material 23 is transmitted to the high thermal conductive honeycomb 22 through the installation portion 12 b of the exhaust passage 12. As a result, the heat transmitted to the high thermal conductivity honeycomb 22 is transmitted to the exhaust gas, and the temperature of the exhaust gas is increased. The oxidation catalyst 13 is heated to the activation temperature by the exhaust gas after the temperature rise.

On the other hand, when the temperature of the exhaust gas exhausted from the engine 11 rises when the engine 11 is sufficiently warmed, the heat of the exhaust gas that has become high temperature is transferred to the heat storage material 23 via the high thermal conductive honeycomb 22 and the installation portion 12b. Given. Then, ammonia desorbs from the heat storage material 23, and the pressure of the reactor 21 rises. When the temperature of the exhaust gas detected by the upstream temperature sensor 27 becomes equal to or higher than the temperature at which ammonia is desorbed from the heat storage material 23, the ECU 50 opens the on-off valve 41. Then, the ammonia desorbed from the heat storage material 23 is returned from the reactor 21 via the connecting pipe 40 to the reservoir 30 and collected. In the reservoir 30, activated carbon physically adsorbs ammonia. Thereafter, when the ammonia recovery rate in the reservoir 30 becomes equal to or higher than a predetermined value, the ECU 50 closes the on-off valve 41.

The ECU 50 determines whether or not to operate the chemical heat storage device 20 as described above. Whether or not the chemical heat storage device 20 is operated is determined by whether or not the chemical heat storage device 20 is ready for operation. When the chemical heat storage device 20 is ready for operation and is ready for operation, the ECU 50 operates the chemical heat storage device 20. On the other hand, when the operation preparation is not complete and the operation is not possible, the ECU 50 does not operate the chemical heat storage device 20.

One requirement for determining whether or not the chemical heat storage device 20 is ready for operation, that is, whether or not the chemical heat storage device 20 is operating, is whether or not the chemical heat storage device 20 operates normally. The exhaust gas temperature detected by the upstream temperature sensor 27, the exhaust gas temperature detected by the downstream temperature sensor 28, the pressure of the reservoir 30 detected by the pressure sensor 31, and the temperature sensor 32. Based on the temperature of the storage device 30 and the like, the ECU 50 determines whether or not the chemical heat storage device 20 operates normally.

If the chemical heat storage device 20 is operating normally, the exhaust gas is heated when passing through the chemical heat storage device 20. For this reason, the temperature of the exhaust gas detected by the downstream temperature sensor 28 is higher than the temperature detected by the upstream temperature sensor 27. On the other hand, if the chemical heat storage device 20 is not operating normally, the exhaust gas is not heated even if it passes through the chemical heat storage device 20. For this reason, the temperature of the exhaust gas detected by the downstream temperature sensor 28 is the same as or slightly different from the temperature detected by the upstream temperature sensor 27. Therefore, the ECU 50 determines whether or not the chemical heat storage device 20 operates normally based on the detection values of the upstream temperature sensor 27 and the downstream temperature sensor 28. That is, the ECU 50 stores whether or not the previous operation of the chemical heat storage device 20 was normal.

Further, in the chemical heat storage device 20, when the on-off valve 41 is opened by the ECU 50, the pressure of the reservoir 30 detected by the pressure sensor 31 varies, and the temperature of the reservoir 30 detected by the temperature sensor 32 varies. . For this reason, when the detected values of pressure and temperature do not change even when the on-off valve 41 is open, a failure of the on-off valve 41, clogging of the connection pipe 40, abnormality of the reservoir 30, abnormality of the reactor 21, etc. are considered. It is done. Therefore, the ECU 50 determines whether or not the chemical heat storage device 20 operates normally based on the detection value of the pressure sensor 31 and the detection value of the temperature sensor 32 when the on-off valve 41 is open.

Another requirement for determining whether or not the chemical heat storage device 20 can be operated is whether or not a predetermined amount of ammonia has been recovered in the reservoir 30, that is, the amount of ammonia stored in the reservoir 30 is a desired exotherm. It is whether it is more than the quantity which can acquire a characteristic. In the chemical heat storage device 20, when the temperature of the exhaust gas is equal to or higher than the temperature at which ammonia is desorbed from the heat storage material 23, the heat of the exhaust gas is given to the heat storage material 23 via the high thermal conductive honeycomb 22 and the installation portion 12b. Then, ammonia is desorbed from the heat storage material 23. The desorbed ammonia moves from the reactor 21 to the reservoir 30 due to a pressure difference when the opening / closing valve 41 is controlled to open. The ammonia is physically adsorbed by the adsorbent in the reservoir 30 and is collected in the reservoir 30.

When the amount of ammonia recovered in the reservoir 30 increases, the pressure in the reservoir 30 increases. Then, based on the pressure detected by the pressure sensor 31 and the temperature detected by the temperature sensor 32, the ECU 50 estimates the ammonia recovery rate in the reservoir 30. The ammonia recovery rate is estimated from the saturated vapor pressure of ammonia, the pressure and temperature of the reservoir 30, and the value of the ammonia adsorption characteristic specific to the adsorbent.

The ECU 50 determines whether or not the ammonia recovery in the reservoir 30 is sufficient based on the estimated ammonia recovery rate. That is, the ECU 50 determines whether or not a predetermined amount of ammonia is adsorbed by the adsorbent of the reservoir 30 based on the estimated ammonia recovery rate. The predetermined amount of ammonia is an amount capable of obtaining desired exothermic characteristics when ammonia is supplied to the heat storage material 23 and undergoes a chemical reaction.

In the present embodiment, for example, a recovery rate of 70% is set as a threshold value for determining that ammonia is sufficiently recovered in the reservoir 30. The recovery threshold is not limited to 70%, and may be set as appropriate, such as 80% or 90%. If the estimated recovery rate is equal to or greater than the threshold, the ECU 50 determines that a predetermined amount of ammonia has been recovered in the reservoir 30. When the estimated recovery rate is less than the threshold value, the ECU 50 determines that ammonia recovery is insufficient.

In the present embodiment, when the chemical heat storage device 20 can operate normally and ammonia is sufficiently collected in the reservoir 30, the ECU 50 determines that the chemical heat storage device 20 is operable, and the chemical heat storage device The device 20 is started. That is, the ECU 50 controls the on-off valve 41 to open. On the other hand, if the chemical heat storage device 20 does not operate normally or ammonia is not sufficiently collected in the storage 30, the ECU 50 determines that the chemical heat storage device 20 is not operable and does not start the chemical heat storage device 20. .

Next, control of the engine 11 by the ECU 50 will be described.
The ECU 50 can take normal control and exhaust priority control as the control of the engine 11. The exhaust priority control of the engine 11 includes, for example, control for increasing the temperature of the exhaust gas exhausted from the engine 11 in order to warm the oxidation catalyst 13 to the activation temperature or higher by the heat of the exhaust gas, or exhaust from the engine 11. Engine control to reduce the amount of air pollutants in the exhaust gas. The normal control of the engine 11 includes control for giving priority to improvement in fuel consumption and control for giving priority to running (output).

Next, the control procedure of the ECU 50 after the engine 11 is started will be described with reference to the flowchart of FIG.
After the engine 11 is started, the ECU 50 performs normal control of the engine 11. Exhaust gas is discharged from the engine 11 into the exhaust passage 12. The ECU 50 first determines whether it is necessary to warm up the oxidation catalyst 13 for exhaust gas purification (step S10). In step S10, the ECU 50 estimates the temperature of the oxidation catalyst 13 by measuring the temperature of the catalyst carrier 12a provided with the oxidation catalyst 13 or measuring the temperature of exhaust gas discharged from the engine 11. . Then, the ECU 50 determines whether or not the estimated temperature is a temperature at which the oxidation catalyst 13 can be activated. The ECU 50 calculates the temperature of the oxidation catalyst 13 from the temperature of the exhaust gas measured by the upstream temperature sensor 27. That is, the ECU 50 calculates the estimated temperature of the oxidation catalyst 13 from the temperature of the exhaust gas upstream of the oxidation catalyst 13. In step S10, if the estimated temperature is lower than the activation temperature of the oxidation catalyst 13, the ECU 50 determines that the oxidation catalyst 13 needs to be warmed up (YES in step S10).

If it is determined YES in step S10, the ECU 50 determines whether the chemical heat storage device 20 is operational. Specifically, the ECU 50 first determines whether or not the chemical heat storage device 20 operates normally (step S11). In step S11, the ECU 50 reads a history before the engine 11 is started. Further, the ECU 50 determines whether or not the chemical heat storage device 20 is operating normally on the basis of the temperature detected by the upstream temperature sensor 27 and the temperature detected by the downstream temperature sensor 28 during the previous operation of the chemical heat storage device 20. Determine whether. Further, the ECU 50 determines whether or not the chemical heat storage device 20 is operating normally based on the pressure and temperature of the storage 30 with the on-off valve 41 open. When the engine 11 is started for the first time, the ECU 50 cannot read the history, and therefore determines YES in step S11.

If it is determined that the chemical heat storage device 20 operates normally (YES in step S11), the ECU 50 shifts the control flow to step S12, and whether or not another requirement is established regarding whether the chemical heat storage device 20 can be operated. Determine whether. That is, in step S12, the ECU 50 determines whether or not the ammonia recovery from the storage 30 is sufficient. The ECU 50 estimates the recovery rate of ammonia in the reservoir 30 based on the pressure in the reservoir 30 detected by the pressure sensor 31 and the temperature in the reservoir 30 detected by the temperature sensor 32. If the estimated recovery rate is equal to or greater than the threshold, the ECU 50 determines that the ammonia recovery is sufficient (YES in step S12). The case where it is determined that the recovery of ammonia is sufficient is a case where the storage amount of ammonia stored in the reservoir 30 is equal to or greater than the amount capable of obtaining desired exothermic characteristics in the reactor 21.

If it is determined that the ammonia recovery is sufficient (YES in step S12), the ECU 50 determines that the chemical heat storage device 20 is operable, and starts the chemical heat storage device 20 while maintaining normal control of the engine 11. Let

If the oxidation catalyst 13 does not need to be warmed up (NO in step S10), the ECU 50 maintains normal control of the engine 11.
When the chemical heat storage device 20 does not operate normally and the chemical heat storage device 20 is out of order, that is, when the chemical heat storage device 20 is not operable (NO in step S11), the ECU 50 starts the engine 11 from normal control. Switch to exhaust priority control to reduce the emission of air pollutants to the outside air.

When it is determined that ammonia recovery is insufficient (NO in step S12), that is, when it is determined that the chemical heat storage device 20 is not operable, the ECU 50 changes the engine 11 from normal control to exhaust priority control. Switch to reduce the emission of air pollutants to the outside air.

Therefore, after the engine 11 is started, if the chemical heat storage device 20 has failed or the chemical heat storage device 20 cannot be operated such that ammonia recovery in the reservoir 30 is insufficient, the ECU 50 Switching from normal control to exhaust priority control, the temperature of exhaust gas is raised by engine control. As a result, the temperature of the exhaust gas immediately after discharge becomes higher than the temperature of the exhaust gas during normal control. Therefore, even if the temperature of the exhaust gas is not raised by the chemical heat storage device 20, the temperature of the exhaust gas rises, and the oxidation catalyst 13 is quickly raised to the activation temperature by the exhaust gas after the temperature rise. .

In addition, after the engine 11 is started, when the chemical heat storage device 20 is operable so that the chemical heat storage device 20 operates normally and ammonia is sufficiently recovered, the ECU 50 maintains normal control of the engine 11. Then, the on-off valve 41 is opened and the chemical heat storage device 20 is started. As a result, the exhaust gas is heated by the chemical heat storage device 20, and the temperature of the exhaust gas rises. Then, the oxidation catalyst 13 is quickly heated to the activation temperature by the exhaust gas after the temperature increase.

Thereafter, when the temperature of the exhaust gas rises to the activation temperature of the oxidation catalyst 13 or more and the warming up of the oxidation catalyst 13 is completed, the ECU 50 closes the on-off valve 41. Further, the ECU 50 switches the engine 11 to normal control.

Next, the control procedure of the ECU 50 during traveling will be described with reference to the flowchart of FIG. It is assumed that the engine 11 is normally controlled by the ECU 50.
During traveling, the ECU 50 determines whether or not the oxidation catalyst 13 needs to be warmed up (step S21). In step S21, the ECU 50 estimates the temperature of the oxidation catalyst 13 by measuring the temperature of the catalyst carrier 12a provided with the oxidation catalyst 13 or measuring the temperature of exhaust gas discharged from the engine 11. . Then, the ECU 50 determines whether or not the estimated temperature is a temperature at which the oxidation catalyst 13 can be activated. The ECU 50 calculates the temperature of the oxidation catalyst 13 from the temperature of the exhaust gas measured by the upstream temperature sensor 27. That is, the ECU 50 calculates the estimated temperature of the oxidation catalyst 13 from the temperature of the exhaust gas upstream of the oxidation catalyst 13. In step S21, if the estimated temperature is lower than the activation temperature of the oxidation catalyst 13, the ECU 50 determines that the oxidation catalyst 13 needs to be warmed up (YES in step S21).

When the oxidation catalyst 13 needs to be warmed up, more specifically, when it is determined that the estimated temperature of the exhaust gas is lower than the activation temperature of the oxidation catalyst 13 (YES in step S21), the ECU 50 performs the control flow. Then, the process proceeds to a step of determining whether the chemical heat storage device 20 can be operated.

First, in step S22, the ECU 50 reads a history. Further, the ECU 50 determines whether or not the chemical heat storage device 20 is operating normally on the basis of the temperature detected by the upstream temperature sensor 27 and the temperature detected by the downstream temperature sensor 28 during the previous operation of the chemical heat storage device 20. Determine whether. Further, the ECU 50 determines whether or not the chemical heat storage device 20 is operating normally based on the pressure and temperature of the storage 30 with the on-off valve 41 open.

If it is determined that the chemical heat storage device 20 is operating normally (YES in step S22), the ECU 50 shifts the control flow to step S23. In step S23, the ECU 50 determines whether or not the ammonia recovery from the reservoir 30 is sufficient. The ECU 50 estimates the recovery rate of ammonia in the reservoir 30 based on the pressure in the reservoir 30 detected by the pressure sensor 31 and the temperature in the reservoir 30 detected by the temperature sensor 32. If the estimated recovery rate is equal to or greater than the threshold, the ECU 50 determines that ammonia recovery is sufficient (YES in step S23).

If it is determined that the ammonia recovery is sufficient (YES in step S23), that is, if it is determined that the chemical heat storage device 20 is operable, the ECU 50 maintains the normal control of the engine 11 while maintaining the normal control of the engine 11. 20 is started.

If it is not necessary to warm up the oxidation catalyst 13, that is, if it is determined that the temperature of the exhaust gas is equal to or higher than the activation temperature (NO in step S21), the ECU 50 maintains the engine 11 in normal control.

When the chemical heat storage device 20 does not operate normally and the chemical heat storage device 20 is out of order (NO in step S22), that is, when the chemical heat storage device 20 is not operable, the ECU 50 starts the engine 11 from the normal control. Switch to exhaust priority control to reduce the emission of air pollutants to the outside air.

When it is determined that the ammonia recovery is insufficient (NO in step S23), that is, when the chemical heat storage device 20 is not operable, the ECU 50 switches the engine 11 from the normal control to the exhaust priority control and returns to the outside air. Reduce emissions of air pollutants.

Therefore, when the temperature of the oxidation catalyst 13 decreases during running and the oxidation catalyst 13 needs to be warmed up, that is, when the temperature of the exhaust gas is lower than the activation temperature, the chemical heat storage device 20 has failed or When the chemical heat storage device 20 in which the ammonia recovery in the storage 30 is insufficient cannot be operated, the ECU 50 switches the engine 11 to the exhaust priority control. Thus, when the oxidation catalyst 13 needs to be warmed up during traveling, the exhaust gas is heated only by engine control and the oxidation catalyst 13 is warmed up without relying on the chemical heat storage device 20.

On the other hand, when the chemical heat storage device 20 is operable even when the oxidation catalyst 13 needs to be warmed up during traveling, the ECU 50 maintains the normal control of the engine 11 while maintaining the normal control of the engine 11. Start. As a result, the exhaust gas is heated by the chemical heat storage device 20, and the temperature of the exhaust gas rises. Then, the oxidation catalyst 13 is quickly heated to the activation temperature by the exhaust gas after the temperature increase. Further, when it is not necessary to warm up the oxidation catalyst 13 during traveling, that is, when the temperature of the exhaust gas is equal to or higher than the activation temperature, the ECU 50 performs normal control of the engine 10 without operating the chemical heat storage device 20. maintain.

According to the above embodiment, the following effects can be obtained.
(1) At the time of cold start of the engine 11, when the chemical heat storage device 20 cannot be operated, the engine 11 is switched to the exhaust priority control. Thereby, the exhaust gas can be quickly heated up to the activation temperature of the oxidation catalyst 13 by engine control. As a result, even if the chemical heat storage device 20 cannot operate, a certain exhaust purification performance can be exhibited by engine control.

(2) When the temperature of the exhaust gas is low as in the cold start of the engine 11 and the chemical heat storage device 20 can be operated, the chemical heat storage device 20 is operated while maintaining normal control of the engine 11. According to this configuration, while giving priority to improving the fuel consumption of the engine 11, the temperature of the exhaust gas is raised by the heat generated by the chemical heat storage device 20, and the oxidation catalyst 13 is brought to the activation temperature by the exhaust gas after the temperature rise. The temperature can be raised quickly. As a result, compared with the case where the oxidation catalyst 13 is warmed up only by heat from the exhaust gas, the oxidation catalyst 13 is warmed up by the chemical heat storage device 20, so that the warming to the activation temperature is suppressed while suppressing the deterioration of fuel consumption. Exhaust gas can be purified by the activated oxidation catalyst 13.

(3) When the temperature of the exhaust gas becomes lower than the activation temperature during traveling, the chemical heat storage device 20 is operated while maintaining the normal control of the engine 11. According to this configuration, the exhaust gas can be quickly heated by the heat generated by the chemical heat storage device 20, and the oxidation catalyst 13 can be quickly heated to the activation temperature by the exhaust gas after the temperature increase. it can. As a result, the exhaust gas can be purified by the oxidation catalyst 13 warmed up to the activation temperature while suppressing the deterioration of fuel consumption.

(4) During driving, if the temperature of the exhaust gas is equal to or higher than the activation temperature, normal control of the engine 11 is maintained without using the chemical heat storage device 20. According to this configuration, the control load on the ECU 50 can be reduced.

(5) In order to warm up the oxidation catalyst 13 with the exhaust gas, the engine 11 is controlled according to the state of the chemical heat storage device 20 to raise the temperature of the exhaust gas. According to this configuration, fuel consumption deterioration can be suppressed as compared with the case where the temperature of the exhaust gas is raised only by engine control. In addition, since the chemical heat storage device 20 is used as an auxiliary for raising the temperature, for example, external energy for auxiliary is not required as compared with the case where an electric heater (EHC) is used.

The above embodiment may be modified as follows.
In the control procedure of the ECU 50 after the engine 11 is started, a condition for starting the chemical heat storage device 20 may be added.

The starting condition of the chemical heat storage device 20 includes, for example, whether or not the temperature of the exhaust gas immediately after being discharged from the engine 11 is equal to or lower than a preset starting temperature. The starting temperature is a temperature lower than the activation temperature of the oxidation catalyst 13 and is a temperature at which the temperature can be raised relatively quickly to the activation temperature of the oxidation catalyst 13. For this reason, if the temperature of the exhaust gas immediately after discharge is higher than the starting temperature, it is more efficient to raise the temperature of the exhaust gas by the chemical heat storage device 20. On the other hand, when the temperature of the exhaust gas immediately after discharge is lower than the starting temperature, the temperature of the exhaust gas is first raised by engine control rather than using the chemical heat storage device 20, and then the chemical heat storage device 20 is turned on when the temperature becomes equal to or higher than the starting temperature. It is more efficient to operate and raise the temperature of the oxidation catalyst 13 to the activation temperature.

According to the control procedure shown in FIG. 5, in step S12, the ECU 50 determines whether or not the start condition is satisfied after determining whether or not the ammonia recovery in the reservoir 30 is sufficient (step S13). . In step S13, when the temperature of the exhaust gas detected by the upstream temperature sensor 27 is equal to or higher than the starting temperature, the starting condition is satisfied (YES in step S13), and the ECU 50 performs chemical control while maintaining the normal control of the engine 11. The heat storage device 20 is started. That is, the ECU 50 controls the on-off valve 41 to open. On the other hand, if the temperature of the exhaust gas detected by the upstream temperature sensor 27 is lower than the start temperature, the start condition is not satisfied (NO in step S13), and the ECU 50 does not start the chemical heat storage device 20 and starts the engine 11 Switch to exhaust priority control.

In this case, when the engine 11 is cold started, the chemical heat storage device 20 can operate normally. However, when the temperature of the exhaust gas is less than the predetermined start temperature, the ECU 50 does not start the chemical heat storage device 20 and does not start the engine 11. Is switched to exhaust priority control. When the exhaust gas is heated to the starting temperature or higher by the exhaust priority control, the ECU 50 returns the engine 11 to the normal control, and thereafter warms the exhaust gas using the chemical heat storage device 20. By doing in this way, the oxidation catalyst 13 can be warmed up more efficiently, suppressing the deterioration of a fuel consumption.

In step S13, when the temperature of the exhaust gas is lower than the starting temperature (NO in step S13), the ECU 50 switches the engine 11 to the exhaust priority control, but the chemical heat storage device 20 may be operated in accordance with this.

In step S10 or step 21, when determining whether or not the oxidation catalyst 13 needs to be warmed up, the ECU 50 determines the oxidation catalyst from the temperature of the exhaust gas upstream of the oxidation catalyst 13 measured by the upstream temperature sensor 27. Although the estimated temperature of 13 was calculated, it is not restricted to this. The ECU 50 may calculate the estimated temperature of the oxidation catalyst 13 from the temperature of the exhaust gas downstream of the oxidation catalyst 13. Further, the ECU 50 may calculate the estimated temperature of the oxidation catalyst 13 from the temperatures of both the upstream and downstream exhaust gases of the oxidation catalyst 13. Further, the temperature of the exhaust gas upstream of the oxidation catalyst 13 may be measured not by the upstream temperature sensor 27 but by the downstream temperature sensor 28, or by both the upstream temperature sensor 27 and the downstream temperature sensor 28. You may measure.

The engine 11 may be a gasoline engine.
In the step of determining whether or not the chemical heat storage device 20 can be operated, two requirements were set: whether or not the chemical heat storage device 20 operates normally and whether or not ammonia is sufficiently recovered. However, the ECU 50 may determine whether or not the chemical heat storage device 20 can be operated based only on whether or not the chemical heat storage device 20 operates normally. In this case, the ECU 50 does not have to determine whether or not ammonia is sufficiently recovered.

In the step of determining whether or not the chemical heat storage device 20 can be operated, another requirement may be added to the two requirements of whether or not the chemical heat storage device 20 operates normally and whether or not ammonia is sufficiently recovered. .

The starting temperature of the chemical heat storage device 20 may be the activation temperature of the oxidation catalyst 13.
As a starting condition of the chemical heat storage device 20, other indicators may be used instead of whether or not the exhaust gas is equal to or higher than the starting temperature. For example, it may be determined whether to start the chemical heat storage device 20 based on the temperature and flow rate of the exhaust gas.

The catalyst may be other than the oxidation catalyst 13 as long as it can purify air pollutants.

Claims

An engine exhaust purification control method using an exhaust purification system including an exhaust gas purification catalyst provided on an exhaust passage through which exhaust gas exhausted from an engine flows, and a chemical heat storage device capable of warming up the catalyst. And
Determining whether the catalyst needs to be warmed up;
And determining whether the chemical heat storage device can be operated.
When it is determined that the catalyst needs to be warmed up and the chemical heat storage device is determined to be operable, the chemical heat storage device is operated to warm up the catalyst,
When it is determined that the catalyst needs to be warmed up and the chemical heat storage device is not operable, the control of the engine is switched to exhaust priority control to discharge air pollutants in the exhaust gas to the outside air An exhaust purification control method for an engine that reduces the engine.
The engine exhaust gas purification control method according to claim 1,
An engine exhaust purification control method, wherein in the step of determining whether or not the catalyst needs to be warmed up, if the estimated temperature of the catalyst is lower than the activation temperature of the catalyst, it is determined that the catalyst needs to be warmed up.
The engine exhaust gas purification control method according to claim 2,
An engine exhaust purification control method for calculating an estimated temperature of the catalyst from at least one of a temperature of the exhaust gas upstream of the catalyst and a temperature of the exhaust gas downstream of the catalyst.
The engine exhaust purification control method according to any one of claims 1 to 3,
The exhaust purification control method for an engine, wherein the exhaust priority control is an engine control for increasing a temperature of the exhaust gas discharged from the engine in order to warm the catalyst to an activation temperature or higher by heat of the exhaust gas.
The engine exhaust purification control method according to any one of claims 1 to 3,
The engine exhaust purification control method, wherein the exhaust priority control is engine control for reducing an amount of the air pollutant in the exhaust gas discharged from the engine.
The engine exhaust purification control method according to any one of claims 1 to 5,
The chemical heat storage device includes a heat storage material and a reactor disposed so as to be capable of exchanging heat with an object to be heated, a storage device that stores a reaction medium that chemically reacts with the heat storage material, the storage device, and the reactor. And a connecting pipe that circulates the reaction medium,
In the step of determining whether or not the chemical heat storage device can be operated, the chemical heat storage device operates normally and the stored amount of the reaction medium stored in the reservoir is greater than or equal to an amount capable of obtaining desired exothermic characteristics. An engine exhaust purification control method for determining that the chemical heat storage device is operable if there is.