JP2022015566A - Reducing agent supply control device and reducing agent supply control method - Google Patents

Abstract

To provide a reducing agent supply control device and a reducing agent supply control method capable of promptly lowering a temperature of exhaust gas.SOLUTION: A reducing agent supply control device controlling a reducing agent supply device that is provided on the upstream side of an NOx removal catalyst removing NOx in exhaust gas in an exhaust pipe in which exhaust gas discharged from an internal combustion engine flows and that supplies a reducing agent into the exhaust pipe includes: a determination section determining whether or not an inlet temperature of the NOx removal catalyst is equal to or higher than a threshold value that is greater than an upper limit value of an active temperature region of the NOx removal catalyst and is smaller than a lower limit value of a temperature region where the NOx removal catalyst can be damaged; and a control section controlling the reducing agent supply device so that supply amount of the reducing agent per unit time in the case where the inlet temperature is equal to or higher than the threshold value becomes larger compared to the case where the inlet temperature is lower than the threshold value.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a reducing agent supply control device and a reducing agent supply control method.

As a system for purifying exhaust gas discharged from an internal combustion engine, for example, a urea SCR (Selective Catalytic Reduction) system is known (see, for example, Patent Document 1).

The urea SCR system includes a urea water injection device (also referred to as an injector or a dosing module) and an SCR catalyst in order from the upstream side in the exhaust pipe through which the exhaust gas flows. The urea water injected into the exhaust pipe from the urea water injection device is hydrolyzed by the heat of the exhaust gas. The ammonia generated thereby is supplied to the SCR catalyst. Then, in the SCR catalyst, NOx in the exhaust gas is reduced to nitrogen.

Japanese Unexamined Patent Publication No. 2009-138737

Since the SCR catalyst needs to be in the active temperature region in order to efficiently purify the exhaust gas, it is desirable that the exhaust gas has a high temperature to some extent. On the other hand, when the temperature of the SCR catalyst becomes higher than the active temperature region, there is a possibility that the SCR catalyst may have a problem such as melting. Therefore, it is necessary to quickly lower the temperature of the exhaust gas before the exhaust gas becomes higher than the active temperature region.

An object of one aspect of the present disclosure is to provide a reducing agent supply control device and a reducing agent supply control method capable of rapidly lowering the temperature of exhaust gas.

The reducing agent supply control device according to one aspect of the present disclosure is provided in the exhaust pipe provided on the upstream side of the NOx purification catalyst for purifying NOx in the exhaust gas in the exhaust pipe through which the exhaust gas discharged from the internal combustion engine flows. A reducing agent supply control device that controls a reducing agent supply device that supplies a reducing agent, wherein the inlet temperature of the NOx purification catalyst is larger than the upper limit of the active temperature region of the NOx purification catalyst, and the NOx purification is performed. A determination unit for determining whether or not the catalyst is equal to or higher than the lower limit of the temperature region in which the catalyst can be damaged, and when the inlet temperature is equal to or higher than the threshold value, as compared with the case where the inlet temperature is lower than the threshold value. A control unit that controls the reducing agent supply device so that the supply amount of the reducing agent per unit time is increased.

The reducing agent supply control method according to one aspect of the present disclosure is provided in the exhaust pipe provided upstream of the NOx purification catalyst for purifying NOx in the exhaust gas in the exhaust pipe through which the exhaust gas discharged from the internal combustion engine flows. A reducing agent supply control method for controlling a reducing agent supply device that supplies a reducing agent, wherein the inlet temperature of the NOx purification catalyst is larger than the upper limit of the active temperature region of the NOx purification catalyst, and the NOx purification is performed. Compared to the step of determining whether or not the catalyst is equal to or higher than the lower limit of the temperature region in which the catalyst can be damaged, and the case where the inlet temperature is equal to or higher than the threshold value, the inlet temperature is lower than the threshold value. It has a step of controlling the reducing agent supply device so that the supply amount of the reducing agent per unit time is increased.

According to the present disclosure, the temperature of the exhaust gas can be rapidly lowered.

Schematic diagram showing a configuration example of the urea SCR system according to the embodiment of the present disclosure. A block diagram showing a configuration example of a control device according to an embodiment of the present disclosure. A flowchart showing an operation example of the control device according to the embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

The configuration of the urea SCR system 100 according to the embodiment of the present disclosure will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration example of the urea SCR system 100 of the present embodiment.

The urea SCR system 100 is a device mounted on a vehicle (for example, a truck, a bus, etc.) (not shown) and purifying the exhaust gas discharged from an internal combustion engine (not shown). The internal combustion engine may be a diesel engine or a gasoline engine. Further, the internal combustion engine is not limited to the internal combustion engine of a vehicle, and may be, for example, an internal combustion engine of a ship or a stationary internal combustion engine.

As shown in FIG. 1, the urea SCR system 100 is provided outside the urea water injection device 2, the temperature sensor 3, the SCR catalyst 4, the ASC (Ammonia Slip Catalyst) 5, and the exhaust pipe 1 provided in the exhaust pipe 1. It has a control device 10 provided.

The solid arrow shown in the exhaust pipe 1 indicates the flow direction of the exhaust gas. Therefore, the urea water injection device 2, the temperature sensor 3, the SCR catalyst 4, and the ASC 5 are provided in the exhaust pipe 1 in order from the upstream side in the flow direction of the exhaust gas.

Although not shown, the upstream end of the exhaust pipe 1 is connected to an exhaust manifold provided in the internal combustion engine. Further, although not shown, the downstream end of the exhaust pipe 1 may face the atmosphere or may be connected to an exhaust diffuser or the like.

The SCR catalyst 4 and the ASC 5 may be housed in a catalyst converter (also referred to as a catalyst casing) connected to the exhaust pipe 1. Further, the catalytic converter may include a urea water injection device 2 and a temperature sensor 3.

The urea water injection device 2 (an example of a reducing agent supply device) is a device that injects urea water (an example of a reducing agent) into the exhaust pipe 1 on the upstream side of the SCR catalyst 4 under the control of the control device 10. The urea water injected by the urea water injection device 2 is hydrolyzed. Ammonia generated thereby (an example of a substance generated from the reducing agent) is supplied to the SCR catalyst 4.

The temperature sensor 3 is provided on the upstream side (near the inlet) of the SCR catalyst 4. The temperature sensor 3 periodically detects the temperature of the exhaust gas near the inlet of the SCR catalyst 4, and notifies the control device 10 of the temperature.

In the present embodiment, the case where the temperature sensor 3 is provided near the inlet of the SCR catalyst 4 and detects the temperature of the exhaust gas at the inlet of the SCR catalyst 4 will be described as an example, but the present invention is not limited to this. For example, the temperature sensor 3 may be provided at a position where the temperature of the SCR catalyst 4 itself can be detected, and the temperature of the SCR catalyst 4 itself may be detected. In the present specification, it is assumed that the temperature of the exhaust gas at the inlet of the SCR catalyst 4 is synonymous with the temperature of the SCR catalyst 4 itself.

The SCR catalyst 4 (an example of a NOx purification catalyst) is a catalyst that reduces NOx in exhaust gas to nitrogen by ammonia generated from urea water.

ASC5 (an example of a decomposition catalyst) is a catalyst that oxidizes and decomposes ammonia that cannot be completely consumed by the SCR catalyst 4. This can prevent ammonia from being discharged into the atmosphere.

The control device 10 (an example of the reducing agent supply control device) is a device that controls the amount of urea water jetted (supplied) from the urea water jet device 2.

The control device 10 is realized by, for example, an ECU (Electronic Control Unit). Although not shown, the control device 10 includes, for example, a CPU (Central Processing Unit), a storage medium such as a ROM (Read Only Memory) containing a control program, a working memory such as a RAM (Random Access Memory), and urea water. It has a communication circuit and the like for communicating with the injection device 2 and the temperature sensor 3. The function of the control device 10 described below (for example, the function of each part shown in FIG. 2) is realized by the CPU reading the control program from the ROM and executing it on the RAM.

Hereinafter, the configuration of the control device 10 will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration example of the control device 10.

As shown in FIG. 2, the control device 10 has a determination unit 11 and a control unit 12.

In the determination unit 11, the temperature detected by the temperature sensor 3 and notified from the temperature sensor 3 (hereinafter referred to as the detected temperature) is the predetermined active temperature region of the SCR catalyst 4 (hereinafter, also simply referred to as the active temperature region). It is determined whether or not it is equal to or greater than the lower limit of the above and whether or not it is equal to or greater than a predetermined threshold value.

The threshold value is, for example, a value larger than the upper limit value of the active temperature region and smaller than the lower limit value of the temperature region in which the SCR catalyst 4 can be damaged (for example, melted). This threshold value is determined based on experiments, simulations, etc. conducted in advance.

When the detection temperature is equal to or higher than the lower limit of the active temperature region and less than the threshold value, the control unit 12 sets the urea water injection device 2 so as to supply the urea water in the predetermined first supply amount into the exhaust pipe 1. Control. The first supply amount is the minimum supply amount per unit time required for purifying NOx.

When the detection temperature is equal to or higher than the threshold value, the control unit 12 controls the urea water injection device 2 so as to supply a predetermined second supply amount of urea water into the exhaust pipe 1. The second supply amount is a supply amount per unit time, which is larger than the first supply amount. For example, the second supply amount may be the maximum amount that the urea water injection device 2 can supply per unit time.

When increasing the supply amount of urea water from the first supply amount to the second supply amount, for example, the amount per injection may be increased.

When the detection temperature becomes less than the threshold value during the supply of the urea water of the second supply amount, the control unit 12 returns the supply amount of the urea water from the second supply amount to the first supply amount.

The configuration of the urea SCR system 100 and the control device 10 has been described above.

Next, the operation of the control device 10 will be described with reference to FIG. FIG. 3 is a flowchart showing an operation example of the control device 10.

The flow shown in FIG. 3 is started, for example, after the internal combustion engine is started, when the detected temperature reaches the lower limit of the active temperature region and the supply of the urea water of the first supply amount is started, and the flow of the internal combustion engine is started. It is repeated during driving.

First, the determination unit 11 determines whether or not the detection temperature is equal to or higher than the threshold value (step S1).

When the detection temperature is not equal to or higher than the threshold value (step S1: NO), the control unit 12 controls the urea water injection device 2 so as to supply the urea water in the first supply amount (step S2). As a result, the urea water injection device 2 executes (including continuation or restart) the supply of the first supply amount of urea water into the exhaust pipe 1.

When the detection temperature is equal to or higher than the threshold value (step S1: YES), the control unit 12 controls the urea water injection device 2 so as to supply the urea water in the second supply amount (step S3). As a result, the urea water injection device 2 executes (including starting, continuing, or restarting) the supply of the second supply amount of urea water into the exhaust pipe 1.

The operation of the control device 10 has been described above.

As described above, according to the present embodiment, when the temperature of the SCR catalyst 4 becomes equal to or higher than the threshold value, the supply amount of urea water is increased. Therefore, the temperature of the exhaust gas can be rapidly lowered by the heat of vaporization of the urea water. Therefore, it is possible to prevent the SCR catalyst 4 from being damaged.

It should be noted that the present disclosure is not limited to the description of the above embodiment, and various modifications can be made without departing from the spirit of the present embodiment. Hereinafter, a modified example will be described.

[Modification 1]
A plurality of temperature regions are divided within a range equal to or higher than the above-mentioned threshold value and smaller than the lower limit of the temperature region in which the SCR catalyst 4 can be damaged, and the higher the temperature region is for each of the plurality of temperature regions, the greater the number. The amount of urea water supplied per unit time may be set stepwise so that the urea water is supplied. Further, for the highest temperature region, the maximum amount that can be supplied by the urea water injection device 2 may be set per unit time.

In this case, the determination unit 11 determines which temperature region of the plurality of temperature regions the detected temperature is included in. Then, the control unit 12 controls the urea water injection device 2 so that the urea water in the supply amount set for the temperature region including the detection temperature is supplied into the exhaust pipe 1.

From the above, in this modification, the supply amount of urea water can be increased or decreased stepwise according to the temperature change of the SCR catalyst 4. Therefore, the temperature of the SCR catalyst 4 can be lowered more efficiently. In addition, waste of the supplied urea water can be eliminated.

[Modification 2]
The SCR catalyst 4 described above may be an SCR-Filter having a filter function for collecting particulate matter in the exhaust gas. The SCR-Filterer is, for example, an integrated SCR catalyst and a DPF (Diesel Particulate Filter).

Further, the urea SCR system 100 shown in FIG. 1 may be configured to include two urea water injection devices 2. In that case, for example, on the upstream side of the urea water injection device 2 shown in FIG. 1, the urea water injection device (hereinafter referred to as the upstream urea water injection device), the SCR catalyst, in order from the upstream side in the flow direction of the exhaust gas. A DOC (Diesel Oxidation Catalyst), a temperature sensor (hereinafter referred to as an upstream temperature sensor), and a DPF may be provided. In this configuration, a hydrocarbon addition injector may be provided between the SCR catalyst and the DOC. Alternatively, for example, on the upstream side of the urea water injection device 2 shown in FIG. 1, the DOC, the upstream urea water injection device, the upstream temperature sensor, the DPF, and the SCR-Filterer are arranged in this order from the upstream side in the flow direction of the exhaust gas. It may be provided. The upstream urea water injection device has the same function as the urea water injection device 2. Further, the upstream temperature sensor is provided near the inlet of the DPF and detects the temperature at the inlet of the DPF.

In the above configuration, the control device 10 is upstream based on the detection temperature of the upstream temperature sensor, as in the control for the urea water injection device 2 based on the detection temperature of the temperature sensor 3 described in the embodiment (see FIG. 3). Controls the side urea water injection device.

As a result, the temperature of the exhaust gas on the upstream side (inlet) of the DPF can be quickly lowered. Therefore, it is possible to prevent the DPF from being damaged by the heat of the exhaust gas.

The reducing agent supply control device and the reducing agent supply control method of the present disclosure are useful for preventing damage to an exhaust gas purification device (catalyst, filter, etc.) that may be damaged by the heat of the exhaust gas.

1 Exhaust pipe 2 Urea water injection device 3 Temperature sensor 4 SCR catalyst 5 ASC
10 Control device 11 Judgment unit 12 Control unit 100 Urea SCR system

Claims (7)

A reducing agent that controls a reducing agent supply device that supplies a reducing agent into the exhaust pipe, which is provided upstream of the NOx purification catalyst that purifies NOx in the exhaust gas in the exhaust pipe through which the exhaust gas discharged from the internal combustion engine flows. It is a drug supply control device,
It is determined whether or not the inlet temperature of the NOx purification catalyst is greater than the upper limit of the active temperature region of the NOx purification catalyst and equal to or greater than the threshold value smaller than the lower limit of the temperature region in which the NOx purification catalyst can be damaged. Judgment unit and
Control to control the reducing agent supply device so that when the inlet temperature is equal to or higher than the threshold value, the supply amount of the reducing agent per unit time is larger than when the inlet temperature is less than the threshold value. With a part,
Reducing agent supply control device. When the inlet temperature is equal to or higher than the threshold value, the amount of the reducing agent supplied is the maximum amount that the reducing agent supply device can supply per unit time.
The reducing agent supply control device according to claim 1. The range above the threshold value and smaller than the lower limit of the temperature region in which the NOx purification catalyst can be damaged is divided into a plurality of temperature regions, and the higher the temperature region is for each of the plurality of temperature regions, the higher the temperature region is. The supply amount of the reducing agent per unit time is set stepwise so that a large amount of the reducing agent is supplied.
The determination unit
It is determined in which of the plurality of temperature regions the inlet temperature is included, and the temperature is determined.
The control unit
The reducing agent supply device is controlled so that the reducing agent is supplied in a set supply amount with respect to the temperature region including the inlet temperature.
The reducing agent supply control device according to claim 1. For the highest temperature region among the plurality of temperature regions, the maximum amount that can be supplied by the reducing agent supply device is set per unit time.
The reducing agent supply control device according to claim 3. The NOx purification catalyst is a selective reduction catalyst that promotes the reduction of NOx by a substance generated from the reducing agent.
The reducing agent supply control device according to any one of claims 1 to 4. The reducing agent is urea water, and the reducing agent is urea water.
The substance is ammonia,
The reducing agent supply control device according to claim 5. A reducing agent that controls a reducing agent supply device that supplies a reducing agent into the exhaust pipe, which is provided upstream of the NOx purification catalyst that purifies NOx in the exhaust gas in the exhaust pipe through which the exhaust gas discharged from the internal combustion engine flows. It is a agent supply control method,
It is determined whether or not the inlet temperature of the NOx purification catalyst is greater than the upper limit of the active temperature region of the NOx purification catalyst and equal to or greater than the threshold value smaller than the lower limit of the temperature region in which the NOx purification catalyst can be damaged. Steps and
When the inlet temperature is equal to or higher than the threshold value, the step of controlling the reducing agent supply device so that the supply amount of the reducing agent per unit time is larger than that when the inlet temperature is lower than the threshold value. And have,
Reducing agent supply control method.

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