JP2017145755A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress a decline in a temperature of an oxidation catalyst.SOLUTION: An exhaust emission control system includes: an oxidation catalyst 21 provided in an exhaust system of an engine 10; a front stage casing 20 provided in the exhaust system to accommodate the oxidation catalyst 21; and a release pipe 50 provided on the exhaust downstream side of the front stage casing 20 in the exhaust system to release exhaust gas to the atmosphere. A downstream end opening 50A of the release pipe 50 is disposed adjacent to the exhaust upstream side of the oxidation catalyst 21 in the exhaust system.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system.

  As this type of exhaust purification system, an oxidation catalyst having HC / CO oxidation ability and a particulate filter that collects particulate matter (hereinafter referred to as PM) in the exhaust in the exhaust passage of the engine in order from the exhaust upstream side. (Hereinafter referred to as a filter) is known. There is a limit to the PM collection capacity of the filter. Therefore, when the PM accumulation amount of the filter reaches a predetermined amount, so-called filter forced regeneration is performed in which HC is supplied to the upstream oxidation catalyst to raise the exhaust gas temperature to the PM combustion temperature, and the PM of the filter is burned and removed. Need to do.

  In order to obtain good oxidation ability of the oxidation catalyst, it is preferable to maintain the catalyst temperature at or above the activation temperature. For example, in Patent Document 1, when performing forced filter regeneration, catalyst temperature increase control is performed in which the combustion temperature in the cylinder is increased by early post injection close to after injection to raise the oxidation catalyst to the activation temperature. Subsequently, a technique is disclosed in which when the oxidation catalyst becomes active, filter temperature increase control is performed to raise the temperature of the filter to the PM combustion temperature by late post injection or exhaust pipe injection.

JP 2012-072666 A

  By the way, depending on the operating state of the engine and the outside air environment, the temperature of the oxidation catalyst may be significantly lower than the activation temperature. If the filter forced regeneration is started in such a low temperature state of the catalyst, the time required for the catalyst temperature increase control becomes long, and there is a problem that the fuel consumption is deteriorated due to an increase in fuel consumption. In addition, there is a problem that the time required until the end of the forced filter regeneration becomes longer.

  The system of an indication aims at controlling the temperature fall of an oxidation catalyst effectively.

  The disclosed system includes an oxidation catalyst provided in an exhaust system of an engine, a first casing provided in the exhaust system and containing the oxidation catalyst, and provided on an exhaust downstream side of the first casing of the exhaust system. And a discharge pipe that discharges exhaust gas to the atmosphere, and a downstream end opening of the discharge pipe is disposed adjacent to the exhaust upstream side of the oxidation catalyst of the exhaust system. .

  An exhaust pipe provided upstream of the first casing of the exhaust system and having an exhaust downstream end connected to an exhaust upstream end of the first casing; and a downstream end opening of the discharge pipe May be disposed adjacent to the exhaust upstream end of the first casing or the exhaust downstream end of the upstream pipe.

  A selective reduction catalyst provided on the exhaust downstream side of the oxidation catalyst of the exhaust system to reduce and purify nitrogen compounds in the exhaust gas using ammonia generated from urea water as a reducing agent; and the first casing of the exhaust system A second casing that is provided upstream of the exhaust and accommodates the selective reduction catalyst, a connecting pipe provided between the first casing and the second casing of the exhaust system, and the connecting pipe An injection nozzle for injecting urea water into the connection pipe, and a first branch pipe branched from the discharge pipe and having a downstream end opening disposed adjacent to the connection pipe. May be.

  A second branch pipe branched from the discharge pipe and having a downstream end opening disposed away from the exhaust upstream side of the oxidation catalyst of the exhaust system; and an upstream side of the second branch pipe Exhaust temperature acquisition means for acquiring the temperature of the exhaust gas flowing through the discharge pipe, and when the exhaust temperature acquired by the exhaust temperature acquisition means is equal to or higher than the activation temperature of the oxidation catalyst, the second branch pipe is shut off, A flow path switching valve that shuts off the exhaust downstream side of the second branch pipe of the discharge pipe when the exhaust temperature acquired by the exhaust temperature acquisition means is lower than the activation temperature of the oxidation catalyst. Good.

  According to the system of an indication, the temperature fall of an oxidation catalyst can be controlled effectively.

It is a typical whole block diagram which shows the exhaust gas purification system which concerns on 1st embodiment. It is a flowchart figure explaining the detail of filter forced regeneration control concerning a first embodiment. (A), (B) is a timing chart figure explaining filter forced regeneration control concerning a first embodiment, and (C) is a timing chart figure explaining conventional filter forced regeneration control. It is a typical whole block diagram which shows the exhaust gas purification system which concerns on 2nd embodiment. It is a typical whole block diagram which shows the exhaust gas purification system which concerns on 3rd embodiment. It is a typical whole block diagram which shows the exhaust gas purification system which concerns on other embodiment.

  Hereinafter, an exhaust purification system according to each embodiment of the present invention will be described with reference to the accompanying drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First embodiment]
As shown in FIG. 1, the exhaust purification system 1A of the first embodiment includes an upstream exhaust pipe 12, a front casing (first casing) 20, a connection exhaust pipe 24, and a rear casing (first casing) in order from the exhaust upstream side. 2 casing) 40 and a discharge exhaust pipe 50. In FIG. 1, reference numeral 10 denotes a diesel engine (hereinafter simply referred to as an engine), reference numeral 11 denotes an exhaust manifold, and reference numeral 30 denotes a urea water injection device.

  The upstream exhaust pipe 12 is formed in a substantially cylindrical shape and extends in the vehicle front-rear direction. The upstream exhaust pipe 12 has an upstream end connected to the exhaust manifold 11 and a downstream end connected to the upstream opening of the front casing 20.

  The front casing 20 is formed in a substantially cylindrical shape, and contains therein a first oxidation catalyst 21 and a filter 22 in order from the exhaust upstream side. In the present embodiment, the first oxidation catalyst 21 and the filter 22 are arranged in series in the front-rear direction of the vehicle.

  The first oxidation catalyst 21 is formed, for example, by supporting a catalyst component or the like on the surface of a ceramic carrier such as a cordierite honeycomb structure. When the first oxidation catalyst 21 is supplied with HC by post injection of the engine 10 or exhaust pipe injection of an exhaust pipe injection nozzle (not shown), the first oxidation catalyst 21 oxidizes this and raises the exhaust temperature.

  The filter 22 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. . The filter 22 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the estimated amount of PM deposition reaches a predetermined amount, forced filter regeneration is performed to remove the PM.

  The connection exhaust pipe 24 extends between the front casing 20 and the rear casing 40 that are adjacently disposed in parallel with each other, and is formed in a substantially S shape by bending its upstream end and downstream end. The connection exhaust pipe 24 has an upstream end connected to the downstream end opening of the front casing 20 and a downstream end connected to the upstream end opening of the rear casing 40. The connection exhaust pipe 24 is provided with a urea water injection nozzle 33 of the urea water injection device 30.

The urea water injection device 30 includes a urea water tank 31 that stores urea water, a urea water pump 32 that pumps urea water from the urea water tank 31, and a urea water injection nozzle 33 that injects urea water into the connection exhaust pipe 24. It has. The urea water injected into the connection exhaust pipe 24 from the urea water injection nozzle 33 is hydrolyzed by exhaust heat to be generated into ammonia (NH ₃ ), and is supplied to the SCR catalyst 41 on the downstream side as a reducing agent.

  The rear casing 40 is formed in a substantially cylindrical shape, and is disposed adjacent to the front casing 20 in parallel. In addition, a selective reduction catalyst (hereinafter referred to as an SCR catalyst) 41 and a second oxidation catalyst 42 are accommodated in the rear casing 40 in order from the exhaust upstream side.

  The SCR catalyst 41 is formed, for example, by supporting zeolite or the like on a porous ceramic carrier. The SCR catalyst 41 adsorbs ammonia supplied as a reducing agent from the urea water injection nozzle 33 and selectively reduces and purifies NOx from the exhaust gas passing through the adsorbed ammonia.

  The second oxidation catalyst 42 is formed, for example, by supporting a catalyst component or the like on the surface of a ceramic carrier such as a cordierite honeycomb structure, and has a function of oxidizing ammonia slipped downstream from the SCR catalyst 41. doing.

  The discharge exhaust pipe (tail pipe) 50 is formed in a substantially cylindrical shape, and its upstream end is connected to the downstream end of the rear casing 40, and at its downstream end, a discharge opening that discharges exhaust gas to the atmosphere. Part 50A is formed. Further, the discharge exhaust pipe 50 is bent toward the front of the vehicle with its upstream end curved in a substantially C shape, and its intermediate portion is located upstream of the front and rear casings 20 and 40 on the front side of the upstream exhaust pipe. 12 is bent in a substantially L-shape and extends in the vehicle width direction, and its downstream end is bent obliquely rearward toward the front casing 20. That is, the discharge opening 50 </ b> A that discharges the exhaust gas to the atmosphere is disposed adjacent to the vicinity of the downstream end of the upstream exhaust pipe 12 and the vicinity of the upstream end of the front casing 20.

  As described above, the discharge opening 50A is disposed adjacent to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20, and the discharge exhaust gas is directly applied, so that the exhaust gas flowing into the oxidation catalyst 21 is kept warm. Thus, the temperature decrease of the oxidation catalyst 21 is effectively suppressed. Further, by applying the exhaust gas from obliquely forward, the exhaust gas can be reliably applied to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20 even under the influence of the vehicle traveling wind. Yes.

  The first exhaust temperature sensor 80 is provided immediately upstream of the oxidation catalyst 21 and acquires the temperature of the exhaust gas flowing into the oxidation catalyst 21 (oxidation catalyst inlet temperature). The second exhaust temperature sensor 81 is provided between the oxidation catalyst 21 and the filter 22 and acquires the temperature of the exhaust gas flowing out from the oxidation catalyst 21 (oxidation catalyst outlet temperature). The differential pressure sensor 82 acquires the differential pressure across the filter 22. Sensor values of these various sensors 80 to 82 are output to an electrically connected electronic control unit (hereinafter referred to as ECU) 100.

  The ECU 100 performs various controls of the engine 10 and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, sensor values of various sensors are input to the ECU 100. The ECU 100 also executes filter forced regeneration control that burns and removes PM accumulated on the filter 22.

  In the forced filter regeneration control, when the PM accumulation amount estimated from the differential pressure before and after the filter acquired by the differential pressure sensor 82 reaches a predetermined upper limit threshold, or the travel distance or regeneration interval of the vehicle reaches a predetermined value. Then it starts.

  The details of the filter forced regeneration control will be described below with reference to FIG. In step S100, it is determined whether the PM accumulation amount has reached a predetermined upper limit threshold value. If the determination is affirmative, the process proceeds to step S110, and the oxidation catalyst temperature acquired from the sensor values of the first and second exhaust temperature sensors 80 and 81 (see FIG. 1) is equal to or higher than a predetermined activation temperature (for example, about 200 degrees). It is determined whether or not. If affirmative, in step S120, HC is supplied to the oxidation catalyst 21 by exhaust pipe injection or late post injection (injection performed when the exhaust valve is opened), and the filter 22 is subjected to PM combustion temperature (for example, about 600 degrees). The filter temperature raising control is performed to raise the temperature up to. On the other hand, if the result is negative, the process proceeds to step S130, where catalyst temperature increase control is performed to raise the oxidation catalyst temperature to the activation temperature by intake throttling or early post injection (injection performed at a timing close to after injection). When the oxidation catalyst temperature reaches the activation temperature in step S140, filter temperature increase control is executed in step S150. When the PM accumulation amount decreases to the predetermined lower limit threshold value in step S160, the filter forced regeneration control is terminated in step S170, and this control is returned.

  In the present embodiment, since the exhaust gas flowing into the oxidation catalyst 21 is kept warm by the discharged exhaust gas, in particular, the determination in step S110 is more frequent (the oxidation catalyst temperature is equal to or higher than the activation temperature), and Even if it is negative (the oxidation catalyst temperature is lower than the activation temperature), the temperature difference between the oxidation catalyst temperature and the activation temperature is effectively reduced.

  As described above in detail, according to the present embodiment, the discharge opening 50A that discharges the exhaust gas to the atmosphere is disposed adjacent to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20 so that the exhaust gas is discharged. It is applied directly to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20. As a result, the exhaust gas flowing into the oxidation catalyst 21 is kept warm by the discharged exhaust gas, and the temperature decrease of the oxidation catalyst 21 can be effectively suppressed.

  In addition, by keeping the oxidation catalyst 21 warm by the exhaust gas, the oxidation catalyst temperature is easily maintained more effectively than the activation temperature. This eliminates the need for catalyst temperature increase control during filter forced regeneration control (see FIG. 3A) or shortens the time required for catalyst temperature increase control (see FIG. 3B). The fuel consumption performance can be improved reliably. Further, the time required for the filter regeneration control can be effectively shortened as compared with the conventional example (see FIG. 3C) in which the oxidation catalyst is not kept warm.

[Second Embodiment]
Next, based on FIG. 4, the detail of the exhaust gas purification system 1B which concerns on 2nd embodiment is demonstrated. The exhaust purification system 1B of the second embodiment is obtained by changing the shape of the discharge exhaust pipe 50 in the exhaust purification system 1A of the first embodiment. Since other configurations are configured in the same manner as in the first embodiment, detailed description thereof is omitted.

  The discharge exhaust pipe 50 of the second embodiment is formed so as to be bifurcated at the downstream end side, and exhaust gas is discharged from the two openings to the atmosphere. The first discharge opening 50A is disposed adjacent to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20 as in the first embodiment. The branch exhaust pipe 51 branches from the downstream end side of the discharge exhaust pipe 50 toward the connection exhaust pipe 24, and the second discharge opening 51A is disposed adjacent to the connection exhaust pipe 24 immediately upstream of the rear casing 40. .

  In the second embodiment, the urea water is diffused by adding the discharged exhaust gas to the upstream exhaust pipe 12 immediately upstream of the oxidation catalyst 21 and directly hitting the connection exhaust pipe 24 immediately upstream of the SCR catalyst 41 in this way. Thus, the inside of the connection exhaust pipe 24 can be effectively kept warm, and the production efficiency of ammonia can be reliably improved.

[Third embodiment]
Next, based on FIG. 5, the detail of 1 C of exhaust gas purification systems which concern on 3rd embodiment is demonstrated. The exhaust purification system 1C of the third embodiment is obtained by further adding a branch discharge pipe 60, a flow path switching valve 61, and a third exhaust temperature sensor 84 to the exhaust purification system 1A of the first embodiment. Since other configurations are configured in the same manner as in the first embodiment, detailed description thereof is omitted.

  The branch discharge pipe 60 branches from the discharge exhaust pipe 50 in the other direction in which the front casing 20 and the upstream pipe 12 do not exist, and the downstream end thereof is open to the atmosphere. The flow path switching valve 61 is, for example, a butterfly valve, and is provided at a branch portion between the discharge exhaust pipe 50 and the branch discharge pipe 60. The flow path switching valve 61 closes the discharge exhaust pipe 50 when the exhaust temperature detected by the third exhaust temperature sensor 84 is lower than a predetermined threshold (for example, the catalyst activation temperature of the oxidation catalyst 21), 3 When the exhaust temperature detected by the exhaust temperature sensor 84 is equal to or higher than a predetermined threshold, the branch pipe 60 is closed. That is, the discharge exhaust gas flow path is configured as the branch discharge pipe 60 when the temperature is low, and is selectively switched to the discharge exhaust pipe 50 when the temperature is high.

  In the third embodiment, as described above, the exhaust gas is directly applied to the downstream end of the upstream exhaust pipe 12 and the upstream end of the front casing 20 only when the discharged exhaust gas is equal to or higher than the activation temperature of the oxidation catalyst 21. It is possible to effectively prevent the oxidation catalyst 21 from being cooled by the low temperature exhaust gas.

[Others]
The present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the spirit of the present invention.

  For example, as shown in FIG. 6, the above embodiments may be combined. Further, the type and arrangement order of the catalyst accommodated in the front casing 20 and the rear casing 40 are not limited to the illustrated example, and may be other catalysts and arrangement orders. The engine 10 is not limited to a diesel engine, and can be widely applied to an internal combustion engine in addition to a gasoline engine or the like.

DESCRIPTION OF SYMBOLS 10 Engine 12 Upstream exhaust pipe 20 Pre-stage casing 21 1st oxidation catalyst 22 Filter 24 Connection exhaust pipe 30 Urea water injection apparatus 31 Urea water tank 32 Urea water pump 33 Urea water injection nozzle 40 Rear stage casing 41 SCR catalyst 42 2nd oxidation catalyst 50 Emission exhaust pipe 100 ECU

Claims (4)

An oxidation catalyst provided in the exhaust system of the engine;
A first casing provided in the exhaust system and containing the oxidation catalyst;
A discharge pipe provided on the exhaust downstream side of the first casing of the exhaust system and discharging exhaust gas to the atmosphere;
An exhaust purification system, wherein a downstream end opening of the discharge pipe is disposed adjacent to an exhaust upstream side of the oxidation catalyst of the exhaust system. An upstream pipe provided on the exhaust upstream side of the first casing of the exhaust system, the exhaust downstream end side of which is connected to the exhaust upstream end of the first casing;
The exhaust purification system according to claim 1, wherein the downstream end opening of the discharge pipe is disposed adjacent to the exhaust upstream end of the first casing or the exhaust downstream end of the upstream pipe. A selective reduction catalyst that is provided downstream of the oxidation catalyst in the exhaust system and that reduces and purifies nitrogen compounds in the exhaust gas using ammonia generated from urea water as a reducing agent;
A second casing provided upstream of the first casing of the exhaust system and containing the selective reduction catalyst;
A connecting pipe provided between the first casing and the second casing of the exhaust system;
An injection nozzle that is provided in the connection pipe and injects urea water into the connection pipe;
The exhaust purification system according to claim 1, further comprising: a first branch pipe branched from the discharge pipe and having a downstream end opening disposed adjacent to the connection pipe. A second branch pipe which branches from the discharge pipe and whose downstream end opening is arranged away from the exhaust upstream side of the oxidation catalyst of the exhaust system;
Exhaust temperature acquisition means for acquiring the temperature of the exhaust gas flowing through the discharge pipe upstream of the second branch pipe;
When the exhaust temperature acquired by the exhaust temperature acquisition means is equal to or higher than the activation temperature of the oxidation catalyst, the second branch pipe is shut off, and the exhaust temperature acquired by the exhaust temperature acquisition means is the activation temperature of the oxidation catalyst. The exhaust gas purification system according to any one of claims 1 to 3, further comprising: a flow path switching valve that shuts off the exhaust downstream side of the second branch pipe of the discharge pipe when the number is less.

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